DIABETES MELLITUS

Comprehensive MD Anaesthesiology Teaching Session

Sources: Miller's Anesthesia 10e | Barash's Clinical Anesthesia 9e | Morgan & Mikhail's Clinical Anesthesiology 7e | Harrison's Principles of Internal Medicine 22e

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1. DEFINITION

Standard Textbook Definition

Clinical Importance

• >420 million people worldwide are affected - it is a global pandemic
• The leading cause of end-stage renal disease, non-traumatic lower limb amputation, and new-onset blindness in adults
• Diabetic patients account for approximately 10-15% of all surgical patients
• Two to four times higher risk of cardiovascular disease compared to non-diabetics
• Perioperative significance: Silent myocardial ischaemia, autonomic neuropathy, gastroparesis (aspiration risk), difficult intubation (stiff joint syndrome), impaired wound healing, and perioperative glycaemic dysregulation make this one of the most clinically consequential comorbidities in anaesthesia

High-Yield Exam Point: "The major perioperative risks to the diabetic patient come from unrecognized or poorly managed coexisting diseases, especially coronary artery disease." - Barash's Clinical Anesthesia 9e (Key Point 6)

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2. INTRODUCTION

Background

Epidemiology

Relevance in Anaesthesia and Critical Care

1. Preoperative: Poor glycaemic control (HbA1c >8.5-9%) is an indication to delay elective surgery
2. Intraoperative: Stress hyperglycaemia, impaired counterregulatory responses, autonomic instability
3. Postoperative: Increased SSI, impaired wound healing, delayed gastric emptying, cardiac events, AKI
4. ICU: Stress hyperglycaemia is near-universal; target glucose 140-180 mg/dL (NICE-SUGAR trial data)
5. Drug interactions: Numerous OHA-anaesthetic drug interactions (metformin-contrast, SGLT-2i-euDKA)

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3. BASIC SCIENCES

A. Anatomy

Pancreatic Islets of Langerhans

• Located throughout the pancreas (~1 million islets)
• Beta (β) cells - 60-70% - produce insulin and C-peptide and amylin
• Alpha (α) cells - 20-25% - produce glucagon
• Delta (δ) cells - 5-10% - produce somatostatin (inhibits both insulin and glucagon)
• F cells (PP cells) - 1-2% - produce pancreatic polypeptide
• Epsilon cells - rare - produce ghrelin

Viva Point: "Why is C-peptide measured?" - C-peptide is co-secreted with insulin in equimolar amounts but is not present in exogenous insulin preparations. A low C-peptide with high insulin indicates exogenous insulin use (factitious hypoglycaemia). A high C-peptide with high insulin suggests insulinoma.

Insulin Gene and Biosynthesis

• Chromosome 11 - INS gene encodes preproinsulin
• Preproinsulin → Proinsulin → Insulin + C-peptide (in Golgi apparatus)
• Insulin is a 51-amino acid peptide (A-chain 21 AA + B-chain 30 AA linked by two disulfide bonds)

B. Physiology of Glucose Homeostasis

Normal Glucose Regulation

• Fasting plasma glucose: 70-99 mg/dL (3.9-5.5 mmol/L)
• Postprandial peak: <140 mg/dL at 2 hours
• Hepatic glucose output (gluconeogenesis + glycogenolysis) = 180 g/day in fasted state

Insulin Secretion (Biphasic Model)

• First phase: Rapid release of pre-formed insulin within 2-5 minutes of glucose exposure (depleted in T2DM)
• Second phase: Sustained release of newly synthesised insulin over 60-120 minutes
• Threshold for secretion: Plasma glucose ~70 mg/dL
• Incretin effect (GLP-1, GIP): Account for 50-70% of postprandial insulin release

Insulin Receptor Signalling

1. Insulin binds to tyrosine kinase receptor (heterotetrameric - 2α + 2β subunits)
2. Auto-phosphorylation of β-subunit → activation of IRS-1 (Insulin Receptor Substrate-1)
3. Activation of PI3-kinase → PKB/Akt pathway → GLUT-4 translocation to cell membrane
4. Parallel MAPK pathway → cell growth, proliferation (responsible for atherosclerosis in insulin resistance)

GLUT Transporters (Anaesthetically Relevant)

Key Concept: GLUT-4 translocation to the cell membrane is the key insulin action. Without insulin, GLUT-4 remains sequestered in intracellular vesicles. This is why hyperglycaemia persists despite high extracellular glucose in T1DM.

Counter-regulatory Hormones (Stress Response)

1. Glucagon - most important acute counter-regulator
2. Epinephrine - stimulates glycogenolysis and gluconeogenesis
3. Cortisol - increases gluconeogenesis, inhibits GLUT-4
4. Growth Hormone - increases lipolysis, induces insulin resistance
5. Cytokines (TNF-α, IL-6) - mediate stress hyperglycaemia

Viva Point: "Why does stress hyperglycaemia occur even in non-diabetics?" - Surgical stress activates the HPA axis and sympathetic nervous system, releasing glucagon, cortisol, epinephrine, and GH, which collectively promote glycogenolysis, gluconeogenesis, and peripheral insulin resistance. Simultaneously, insulin secretion is paradoxically suppressed by alpha-adrenergic stimulation of β-cells.

C. Pathophysiology

Type 1 DM - "Ominous Octet" (T-cell Mediated)

1. Genetic susceptibility - HLA-DR3, HLA-DR4 (>90% of T1DM patients)
2. Environmental trigger - viral infection (Coxsackie B4, rubella, CMV), toxins
3. Autoimmune T-cell activation against β-cell antigens
4. Autoantibodies: Anti-GAD65 (Glutamic Acid Decarboxylase), Anti-IA-2, Anti-insulin (IAA), Anti-ZnT8
5. Progressive β-cell destruction (90%+ destruction before clinical onset)
6. Absolute insulin deficiency → Hyperglycaemia + Ketosis

• Absolute insulin deficiency + glucagon excess
• Uninhibited lipolysis → Free Fatty Acids → β-oxidation → Acetyl CoA accumulation → Ketone bodies (acetoacetate, β-hydroxybutyrate, acetone)
• Anion gap metabolic acidosis: AG = Na - (Cl + HCO3) - normal 8-12 mEq/L; in DKA, AG >20 mEq/L
• Total body potassium depletion despite initial hyperkalaemia (acidosis drives K+ extracellularly)

Type 2 DM - The "Ominous Octet" of DeFronzo

1. Pancreas - decreased insulin secretion, increased glucagon (α-cell dysfunction)
2. Liver - increased hepatic glucose production (gluconeogenesis)
3. Muscle - decreased glucose uptake (insulin resistance)
4. Adipose tissue - increased lipolysis → increased FFA (promotes insulin resistance)
5. Gut - decreased incretin effect (reduced GLP-1 response)
6. Kidney - increased glucose reabsorption by SGLT-2
7. Brain - insulin resistance, increased appetite
8. Hypothalamus - neurotransmitter dysregulation

Hyperglycaemic Hyperosmolar State (HHS) (Type 2)

• Extreme hyperglycaemia (usually >600 mg/dL), without significant ketosis
• Sufficient insulin present to prevent lipolysis/ketogenesis, but insufficient for glucose utilisation
• Serum osmolarity >320 mOsm/kg
• Profound dehydration, neurological symptoms

Advanced Glycation End-Products (AGEs)

• Non-enzymatic glycation of proteins by excess glucose
• Glycated haemoglobin (HbA1c) - most clinically useful marker
• Glycation of collagen → Stiff Joint Syndrome (affects cervical spine and TMJ - airway relevance)
• Glycation of myelin → Peripheral neuropathy
• Glycation of vascular endothelium → Atherosclerosis

D. Pharmacology of Key Drugs (Overview - detailed in Section 10)

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4. CLASSIFICATION

ADA Classification (2024)

1. Type 1 DM

• 1A: Immune-mediated (classic T-cell destruction, positive autoantibodies)
• 1B: Idiopathic (negative autoantibodies, ketosis-prone)
• LADA (Latent Autoimmune Diabetes in Adults): Slowly progressive T1DM in adults; initially resembles T2DM

2. Type 2 DM

• Insulin resistance + progressive β-cell dysfunction
• Accounts for 90-95% of all DM

3. Gestational Diabetes Mellitus (GDM)

• Diagnosed in the 2nd or 3rd trimester in a previously non-diabetic patient
• Screened at 24-28 weeks with 75g OGTT (IADPSG criteria)
• May or may not persist postpartum

4. Other Specific Types

Viva Point: "What is MODY?" - Maturity-Onset Diabetes of the Young is a monogenic (autosomal dominant) form of DM, usually presenting before age 25, with no autoimmunity and no absolute insulin deficiency. MODY-2 (glucokinase mutation) is the mildest form; MODY-3 (HNF-1α mutation) is the most common and responds to sulfonylureas.

Staging (ADA 2024 - Staging of Type 1 DM)

Prediabetes Classification

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5. ETIOLOGY AND RISK FACTORS

Risk Factors for Type 1 DM

• HLA-DR3 and HLA-DR4 genotype (inherited)
• First-degree relative with T1DM (5-15% risk)
• Environmental triggers: Coxsackie B virus, enterovirus, cow's milk proteins (controversial), vitamin D deficiency

Risk Factors for Type 2 DM

Risk Factors for Perioperative Complications in Diabetics

1. Poor glycaemic control (HbA1c >8.5%) - most important
2. Autonomic neuropathy - haemodynamic instability, aspiration risk
3. Peripheral neuropathy - masking of pain symptoms
4. Nephropathy (CKD) - AKI risk, drug dosing issues
5. Cardiovascular disease - silent ischaemia, cardiomyopathy
6. Obese T2DM - difficult airway, OSA, GERD

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6. CLINICAL FEATURES

Symptoms

Classic Symptoms ("4 P's") of Hyperglycaemia

1. Polyuria - osmotic diuresis (glucose threshold for renal excretion: ~180 mg/dL)
2. Polydipsia - secondary to polyuria and hyperosmolality
3. Polyphagia - cellular starvation despite hyperglycaemia
4. Weight loss - catabolism of fat and protein for energy (especially T1DM)

Additional Symptoms

• Blurred vision (osmotic lens changes)
• Fatigue and weakness
• Recurrent infections (fungal skin infections, vaginitis, UTIs)
• Slow wound healing
• Paraesthesias (peripheral neuropathy)
• Postural dizziness (autonomic neuropathy)
• Early satiety, nausea, postprandial bloating (gastroparesis)

Signs

Stiff Joint Syndrome (Prayer Sign) - Anaesthetic Relevance

• Due to glycation of collagen in joints and periarticular tissues
• Affects cervical spine and atlanto-occipital joint → restricted neck extension
• Affects temporomandibular joint → limited mouth opening
• Prayer Sign: Patient cannot oppose palmar surfaces of fingers due to flexion contractures
• Predicts difficult laryngoscopy - documented in up to 30% of T1DM patients with longstanding disease

Clinical Pearl: Always perform the Prayer Sign test in long-standing T1DM patients during preoperative airway assessment. A positive sign (inability to appose palmar surfaces) is associated with difficult intubation.

Examination Findings Relevant to Anaesthesia

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7. DIAGNOSIS

Diagnostic Criteria (ADA 2024)

Laboratory Investigations

Routine (All Diabetic Patients Preoperatively)

Special Tests

• C-peptide: Differentiates T1DM (low) from T2DM (normal/high) or insulinoma (high)
• Anti-GAD65, Anti-IA-2, Anti-ZnT8 antibodies: Confirm T1DM autoimmunity
• Fructosamine: Reflects 2-week average glucose control (useful when HbA1c unreliable - e.g., haemolytic anaemia, haemoglobinopathy)
• Echocardiogram: If cardiomyopathy suspected
• 24-hour ambulatory BP/Holter monitoring: If autonomic neuropathy suspected

Monitoring Parameters

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8. MANAGEMENT

Medical Management (Non-anaesthetic)

Lifestyle Modification (First-line for T2DM)

• Diet: Low glycaemic index, caloric restriction (500 kcal/day deficit for weight loss)
• Exercise: 150 min/week moderate-intensity aerobic exercise
• Weight loss: 5-7% body weight reduction significantly reduces DM progression

Pharmacological - Stepwise T2DM Management (ADA 2024)

• ASCVD present → SGLT-2i (empagliflozin/canagliflozin) or GLP-1RA (semaglutide/liraglutide)
• HF or CKD → SGLT-2i
• Weight loss needed → GLP-1RA or SGLT-2i
• Hypoglycaemia avoidance → DPP-4i, GLP-1RA, SGLT-2i
• Cost limitation → Sulfonylurea or thiazolidinedione

Glycaemic Targets (Harrison's Principles 22e)

Management of DKA

Diagnostic Criteria for DKA

DKA Management (5 Pillars)

1. Fluid resuscitation (most important initial step)
   • 0.9% NaCl: 1L in first hour, then 500 mL/hr x 4h, then 250 mL/hr based on haemodynamics
   • Switch to 0.45% NaCl when glucose <250 mg/dL + pH >7.3
   • Add dextrose 5% when glucose reaches 200-250 mg/dL
2. Insulin therapy
   • Regular insulin IV infusion: 0.1 units/kg/hr (start AFTER K+ >3.5 mEq/L)
   • OR 0.1 units/kg IV bolus then 0.1 units/kg/hr
   • Target glucose reduction: 50-75 mg/dL/hour (not faster - cerebral oedema risk)
   • When glucose <250 mg/dL + pH >7.3 → switch to SC insulin; continue infusion 1-2h overlap
3. Potassium replacement (most dangerous electrolyte issue)
   • K+ <3.5 mEq/L: Replace first; do NOT start insulin
   • K+ 3.5-5.0 mEq/L: Add 20-40 mEq K+ per litre of IV fluid
   • K+ >5.0 mEq/L: No K+ supplementation; check K+ hourly
4. Bicarbonate (controversial)
   • Consider ONLY if pH <7.0
   • Give 100 mEq NaHCO3 in 400 mL sterile water + 20 mEq KCl over 2 hours
5. Identify and treat precipitant (Infection most common - "6 I's")
   • Infection, Insulin omission, Ischaemia (MI/stroke), Infarction, Intoxication, Iatrogenic (steroids)

Viva Point: "Why should you NOT give insulin if K+ <3.5 mEq/L?" - Insulin drives K+ intracellularly (via Na/K-ATPase stimulation). Starting insulin in a hypokalaemic patient can precipitate life-threatening hypokalaemia causing cardiac arrhythmias.

Management of HHS (Hyperosmolar Hyperglycaemic State)

• Goal: Reduce osmolarity by ~3-8 mOsm/kg/hr (not too fast - cerebral oedema)
• Fluids: 0.9% NaCl initially, switch to 0.45% when haemodynamically stable
• Insulin: Lower doses than DKA (0.05 units/kg/hr), start only after fluids
• Target glucose: 250-300 mg/dL (avoid rapid lowering - cerebral oedema)
• Anticoagulation: Consider DVT prophylaxis (hyperosmolality → hypercoagulability)

Hypoglycaemia Management

Rule of 15: Give 15g fast-acting carbohydrate, recheck in 15 minutes, repeat if still <70 mg/dL

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9. ANAESTHETIC CONSIDERATIONS

A. Preoperative Assessment and Optimisation

History (Focus Areas for DM Patient)

1. Type of DM and duration (T1DM >10 years → high risk of complications)
2. Current medications and doses
3. Usual glycaemic control - ask for glucometer diary, HbA1c records
4. Hypoglycaemia episodes - especially unawareness
5. Autonomic symptoms - postural dizziness, early satiety, constipation, sweating
6. Cardiovascular - chest pain (angina), dyspnoea, palpitations
7. Renal - known CKD, proteinuria
8. Airway - neck stiffness, difficulty opening mouth
9. Neuropathy - paraesthesias, weakness
10. Previous surgical/anaesthetic history

Preoperative Investigations

• Mandatory: FBS, electrolytes, creatinine/eGFR, ECG, urinalysis
• Recommended: HbA1c (if not done in past 3 months), lipid profile
• Selective: Echocardiography (if cardiac symptoms), 24h Holter (autonomic neuropathy), chest X-ray (CCF)

Preoperative Optimisation

• Target HbA1c <8.5% before elective surgery (AAGBI); delay if ≥8.5%
• Target HbA1c <9% (Australian Diabetes Association guideline)
• Optimise cardiovascular status, BP, renal function
• Schedule surgery as first case of the day (minimises fasting duration)
• Ideal preoperative morning glucose: 100-180 mg/dL

Perioperative Medication Management

HIGH-YIELD EXAM POINT - SGLT-2 Inhibitors: Stop 24 hours before minor surgery and 72 hours before major surgery. Reason: SGLT-2 inhibitors cause euglycaemic DKA - DKA with normal/near-normal glucose (<250 mg/dL), which is easily missed. The mechanism is increased glucagon/insulin ratio + ketogenesis, unmasked by fasting and surgical stress. (Miller's 10e, p. 3968)

HIGH-YIELD EXAM POINT - GLP-1 Agonists (2025 ADS/ANZCA guideline): Due to delayed gastric emptying caused by GLP-1 agonists (e.g., semaglutide, liraglutide, exenatide), there is risk of aspiration despite adequate fasting. The 2025 ADS/ANZCA/GESA/NACOS guidelines recommend: Stop weekly GLP-1 agonists 7 days before surgery; stop daily GLP-1 agonists on the day of surgery. Consider RSI if not stopped appropriately. (PMID: 40814081)

B. Airway Implications

Difficult Airway Risk Factors in DM

1. Stiff Joint Syndrome - glycation of cervical spine + TMJ collagen
   • Positive Prayer Sign = predictor of difficult laryngoscopy
   • Up to 30% of longstanding T1DM patients
2. Obesity (especially T2DM) - reduced FRC, obstructive sleep apnoea, difficult mask ventilation
3. Autonomic neuropathy - impaired airway reflexes, gastroparesis (full stomach risk)
4. Macroglossia (in hypothyroidism associated with DM - rare)

Airway Management Strategy

• Always assess airway in preoperative clinic (Prayer Sign, neck extension, mouth opening, Mallampati, thyromental distance)
• If stiff joint syndrome or obesity: prepare for videolaryngoscopy
• If gastroparesis/delayed gastric emptying: consider RSI or awake fibreoptic intubation
• Metoclopramide (10 mg IV) and ranitidine/PPI preoperatively for gastroparesis

C. Intraoperative Anaesthetic Management

Monitoring

• Standard: ECG, SpO2, NIBP (every 5-15 min), capnography, temperature
• Blood glucose: Every 30-60 minutes intraoperatively
• Additional: Invasive arterial line for major surgery/labile glucose, CVP for major fluid shifts
• Urine output: Foley catheter for procedures >2h

Glucose Targets - Intraoperative

Intraoperative Glucose-Insulin Management

• Omit morning oral hypoglycaemics
• Check glucose preoperatively, intraoperatively at 1h, postoperatively
• If glucose >180 mg/dL → SC regular insulin correction dose

• Use an insulin infusion pump (Regular insulin 50 units in 50 mL 0.9% NaCl = 1 unit/mL)
• Adjust infusion rate according to a sliding scale based on hourly capillary blood glucose
• Run a separate 10% dextrose at 80-100 mL/hr to provide substrate
• Add KCl (10-20 mEq) to dextrose bag to prevent hypokalaemia
• Target: 100-180 mg/dL intraoperatively

Drug Selection in Diabetic Patients

Regional vs General Anaesthesia in DM

1. Reduces stress hyperglycaemia (suppresses sympatho-adrenal response)
2. Allows monitoring of sensorium (early detection of hypoglycaemia)
3. Reduced opioid requirement → faster return of GI motility (important in gastroparesis)
4. Less postoperative nausea/vomiting

• Pre-existing peripheral neuropathy → document neurological status carefully pre-block
• Consent patient about pre-existing sensory deficits
• Avoid injecting into areas of skin infection (increased risk in DM)
• Autonomic neuropathy → more pronounced hypotension with spinal/epidural (prepare vasopressors)
• Phenylephrine preferred over ephedrine as vasopressor (ephedrine increases glucose via beta-adrenergic stimulation)

Exam Point: Spinal anaesthesia causes more profound hypotension in diabetics with autonomic neuropathy. Have vasopressors ready. Phenylephrine is preferred over ephedrine in diabetics because ephedrine stimulates glycogenolysis.

Ventilation Strategies

• DKA patients on ventilator: Maintain PaCO2 matching the metabolic compensation (do NOT normalize if metabolic acidosis persists - this can cause paradoxical CSF acidosis)
• Avoid hyperventilation in DKA - target PaCO2 = 1.5 × [HCO3] + 8 ± 2 (Winter's formula)
• Obese T2DM patients: Higher PEEP (5-10 cmH2O), prone to atelectasis, lung-protective ventilation

D. Postoperative Care

Immediate Post-anaesthesia

• Monitor glucose every 1-2 hours in PACU
• Target 140-180 mg/dL
• Resume SC insulin when eating
• Watch for hypoglycaemia (masked by residual sedation, autonomic neuropathy)
• Adequate pain control (stress response causes hyperglycaemia)
• Early enteral feeding promotes better glycaemic control than TPN

Wound Care

• Strict aseptic technique; DM patients have 2-3x increased SSI risk
• Optimise perioperative glucose (each 50 mg/dL rise in glucose → 30% increase in SSI risk)

E. ICU Management

Glycaemic Management in ICU (Based on NICE-SUGAR Evidence)

• 6,104 critically ill patients (medical + surgical)
• Intensive control (81-108 mg/dL) vs Standard control (144-180 mg/dL)
• Result: 90-day mortality HIGHER in intensive group (27.5% vs 24.9%; p=0.02)
• Severe hypoglycaemia more common in intensive group (6.8% vs 0.5%)
• Conclusion: Target 140-180 mg/dL in ICU patients; intensive control is HARMFUL

• 1,548 surgical ICU patients
• IIT (80-110 mg/dL) vs Standard (180-200 mg/dL)
• 42% relative reduction in ICU mortality with IIT
• HOWEVER: Patients received significant exogenous glucose (TPN-heavy) - may explain results
• Results NOT replicated in subsequent studies

HIGH-YIELD EXAM POINT: "Very tight control of perioperative blood glucose levels appears to increase the risk of hypoglycaemic complications without clearly reducing the risk of hyperglycaemic complications." - Barash's 9e (Key Point 7)

ICU Protocol - IV Insulin Infusion

1. Start insulin infusion when glucose >180 mg/dL
2. Regular insulin: 50 units in 50 mL NS (1 unit/mL)
3. Check glucose hourly (or every 30 min if unstable)
4. If glucose <70 mg/dL: Stop infusion; give 25 mL 50% dextrose; recheck in 15 min
5. Provide minimum 150g glucose/day to prevent starvation ketosis
6. Enteral nutrition preferred over TPN for glycaemic control

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10. DRUGS

A. INSULIN

Types of Insulin

Insulin Mechanism of Action

• Binds insulin receptor (tyrosine kinase receptor) → IRS-1 phosphorylation → PI3K/Akt → GLUT-4 translocation
• Also: Stimulates glycogen synthesis, inhibits gluconeogenesis, promotes lipogenesis, inhibits lipolysis, promotes protein synthesis

Intravenous Insulin (Perioperative Use)

• Only Regular Insulin is used intravenously
• Rapid-acting analogues (lispro, aspart) - NOT approved for IV use in most guidelines
• Dose: 0.05-0.1 units/kg/hr for infusion; titrate to glucose
• Hypoglycaemia treatment (IV): 25-50 mL of 50% dextrose (12.5-25g glucose)

Anaesthetic Relevance of Insulin

• Insulin adsorbs to PVC tubing (up to 30% loss) - flush tubing with insulin solution before connecting to patient
• Subcutaneous absorption altered by temperature (hypothermia reduces absorption; on rewarming, sudden surge)
• Insulin resistance increases dramatically with surgical stress

B. METFORMIN

KEY EXAM POINT: The risk of lactic acidosis with metformin occurs when tissue perfusion is impaired (surgery, contrast nephropathy, shock). Metformin inhibits mitochondrial complex I → impairs lactate clearance. The absolute risk is very low but the consequences are severe. Hence, hold perioperatively.

C. SULFONYLUREAS

D. GLP-1 RECEPTOR AGONISTS (Incretin Mimetics)

2025 UPDATE (PMID: 40814081): The 2025 ADS/ANZCA/GESA/NACOS clinical practice recommendations specifically address perioperative GLP-1 agonist management. For elective procedures: stop weekly GLP-1RA 7 days before, daily GLP-1RA on the day before. If not stopped, treat as full stomach - RSI and consider gastric ultrasound.

E. SGLT-2 INHIBITORS

How to recognise Euglycaemic DKA:

• Nausea, vomiting, abdominal pain POSTOPERATIVELY
• Glucose NORMAL or mildly elevated (<250 mg/dL) - misleadingly reassuring
• Blood gas: Metabolic acidosis, raised AG
• Serum/urine ketones: POSITIVE
• Check ketones in ALL postoperative SGLT-2i patients (even with normal glucose)

F. DPP-4 INHIBITORS (Gliptins)

G. THIAZOLIDINEDIONES (Glitazones)

H. GLUCAGON

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11. SCORES, FORMULAE, AND NUMERICAL VALUES

Key Numerical Values

Important Formulae

1. Anion Gap (AG)

• Normal: 8-12 mEq/L (with albumin correction: 8-16 mEq/L)
• DKA: Typically >20 mEq/L

2. Albumin-Corrected Anion Gap

• Essential in ICU where hypoalbuminaemia is common

3. Osmolar Gap and Calculated Serum Osmolarity

• Normal: 280-295 mOsm/kg
• HHS: >320 mOsm/kg

4. Corrected Sodium in Hyperglycaemia

5. HbA1c - Average Glucose Conversion

6. Winter's Formula (Expected PaCO2 in Metabolic Acidosis)

• Used to verify adequate respiratory compensation in DKA
• If actual PaCO2 < expected → respiratory alkalosis also present
• If actual PaCO2 > expected → concomitant respiratory acidosis

7. Insulin Infusion Rate Calculation (GIK Regimen)

• Normal hepatic glucose output = 2-3 mg/kg/min
• TPN glucose provision: Target ≤5 mg/kg/min

8. Body Mass Index (BMI) - Relevant for T2DM

• Overweight: 25-29.9; Obese class I: 30-34.9; Class II: 35-39.9; Class III (morbid): ≥40
• BMI >30 → increased T2DM risk; BMI >35 → bariatric surgery indication if DM present

Scoring Systems

1. HbA1c-Based Surgery Delay Guidelines

2. Revised Cardiac Risk Index (RCRI) - Lee Index

• RCRI 0: 0.4% MACE risk; 1: 0.9%; 2: 6.6%; ≥3: 11%+

3. DKA Severity Grading (ADA)

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12. GUIDELINES

Current Evidence-Based Guidelines (2024-2025)

1. ADA Standards of Medical Care in Diabetes (2024)

• HbA1c target: <7% for most non-pregnant adults
• Perioperative glucose target: 140-180 mg/dL
• ICU insulin infusion start threshold: >180 mg/dL
• Preoperative evaluation: Includes ECG, renal function, HbA1c
• SGLT-2i: Hold before surgery

2. AAGBI/Centre for Perioperative Care (CPOC) UK Guidelines (2021)

• Delay elective surgery if HbA1c ≥8.5%
• Schedule DM patients as first on morning list
• Monitoring every 30-60 min intraoperatively
• VRII (Variable Rate Insulin Infusion) preferred over fixed-rate GIK
• SGLT-2i: Hold 24h (minor) to 72h (major) before surgery

3. NICE-SUGAR Trial (NEJM 2009) - Practice Changing

• Target glucose 140-180 mg/dL in ICU (NOT tight control 80-110 mg/dL)
• Intensive insulin therapy increases mortality in critically ill patients

4. 2025 ADS/ANZCA/GESA/NACOS Guidelines for GLP-1RA (PMID: 40814081)

• Daily GLP-1RA: Stop on day before surgery
• Weekly GLP-1RA (semaglutide): Stop 7 days before surgery
• If not stopped: Treat as full stomach - RSI, consider gastric ultrasound
• Strong recommendation for preoperative gastric ultrasound assessment when GLP-1RA not held

5. ACC/AHA Perioperative Guidelines (2024)

• DM (insulin-treated) counted as 1 point in RCRI
• Recommend perioperative statin, aspirin continuation in DM with ASCVD
• Beta-blocker continuation (if already on therapy)

6. Continuous Glucose Monitoring (CGM) Perioperative Use (PMID: 40613260)

• Systematic review (2025) demonstrates CGM can be used perioperatively
• Flash glucose monitoring (FreeStyle Libre) - accuracy maintained in most surgical settings
• CGM does NOT replace capillary blood glucose checks during major haemodynamic changes (hypoperfusion → CGM inaccurate)
• Not yet standard of care but emerging as important tool

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13. IMPORTANT TABLES

Table 1: Type 1 vs Type 2 DM - Comprehensive Comparison

Table 2: Antidiabetic Drug Perioperative Management

Table 3: Chronic Complications of DM and Anaesthetic Implications

Table 4: DKA vs HHS - Differential Diagnosis

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14. FLOWCHARTS AND ALGORITHMS

Algorithm 1: Preoperative Management of Diabetic Patient

DIABETIC PATIENT SCHEDULED FOR SURGERY
                    ↓
         PREOPERATIVE ASSESSMENT
    (HbA1c, FBS, ECG, eGFR, electrolytes)
                    ↓
         Is HbA1c ≥8.5%?
           /            \
         YES              NO
          ↓                ↓
   Elective Surgery?   Proceed with surgery
      /       \
    YES         NO
     ↓           ↓
  DELAY       Proceed
  Optimise    (emergency)
  Control       ↓
     ↓      Enhanced monitoring
  Reassess    (glucose q30-60min)
  in 6-8 wks
                    ↓
         MEDICATION MANAGEMENT
    ↙        ↓         ↓        ↘
 SGLT-2i  GLP-1RA  Metformin  Sulfo/Glinides
 72h/24h   Daily:   Hold day   Hold morning
 HOLD     1d before  of surgery  of surgery
          Weekly:
          7d before
                    ↓
        SCHEDULE AS FIRST MORNING CASE
                    ↓
   TARGET PREOPERATIVE GLUCOSE 100-180 mg/dL

Algorithm 2: Intraoperative Glucose Management

CHECK GLUCOSE ON ARRIVAL TO OT
              ↓
    Glucose 100-180 mg/dL?
      /           |           \
  <100 mg/dL   YES          >180 mg/dL
     ↓           ↓               ↓
  Treat       Proceed       Start VRII
  Hypoglycaemia Monitoring    (Insulin infusion)
  25-50 mL    q30-60 min
  50% Dextrose              ↓
     ↓                  Adjust rate
  Recheck                per scale
  15 min                    ↓
                      Monitor q30 min
                            ↓
                    If glucose <100:
                    ↓ insulin rate,
                    add dextrose
                            ↓
                   TARGET: 140-180 mg/dL

Algorithm 3: DKA Management

DIAGNOSIS: Glucose >250 + Ketones + pH <7.3
                    ↓
         SIMULTANEOUS ACTIONS:
    ABC, IV access x2, Foley catheter
                    ↓
        CHECK K+ BEFORE INSULIN
              ↓
    K+ <3.5?      K+ 3.5-5.0?     K+ >5.0?
       ↓               ↓               ↓
   REPLACE K+    Start Insulin    Start Insulin
   FIRST         + KCl 20-40 mEq   No KCl
   (NO INSULIN   per litre         Check K+ hourly
   until K+>3.5)
              ↓
     FLUID RESUSCITATION
   0.9% NaCl 1L first hour
   then 500 mL/hr x 4h
   then 250 mL/hr based on hemodynamics
              ↓
     INSULIN: 0.1 units/kg/hr IV
     Target BG reduction: 50-75 mg/dL/hr
              ↓
     When BG <250 AND pH >7.3:
   Switch to 5% Dextrose + continue insulin
              ↓
     RESOLUTION: pH >7.3 + HCO3 >18 + AG <12
              ↓
   Transition to SC insulin (1-2h overlap)
              ↓
     IDENTIFY PRECIPITANT
   (Infection most common - 6 I's)

Algorithm 4: Perioperative Hypoglycaemia Management

GLUCOSE <80 mg/dL IN PERIOPERATIVE PERIOD
              ↓
   Is patient awake and cooperative?
         /                    \
       YES                     NO
        ↓                       ↓
   15g fast-acting          IV ACCESS PRESENT?
   carbohydrate              /              \
   (Rule of 15)            YES               NO
        ↓                   ↓                ↓
   Recheck 15 min    25-50 mL 50%       Glucagon
                     Dextrose IV        1 mg IM/SC
                     (12.5-25g)
              ↓
         Recheck BG in 15 min
              ↓
      Still <80 mg/dL?
           /      \
         YES       NO
          ↓         ↓
       Repeat    Continue monitoring
       treatment  q15 min x 1 hour
          ↓
    Consider D5 or D10 infusion
    Notify endocrine/physician

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15. FREQUENTLY ASKED MD VIVA QUESTIONS

Short Viva Questions

1. Resting tachycardia - due to vagal denervation
2. Fixed heart rate - no R-R interval variability - confirmed by deep breathing test (normal: HR varies by ≥15 bpm)
3. Orthostatic hypotension - due to loss of sympathetic vasoconstrictor tone (drop >20 mmHg systolic or >10 mmHg diastolic on standing)
4. Impaired cardiovascular responses to anaesthesia - severe hypotension on induction
5. Silent myocardial ischaemia - loss of cardiac pain afferents
6. Gastroparesis - vagal denervation of stomach → delayed emptying → full stomach → aspiration risk - use RSI
7. Bladder dysfunction - urinary retention (Foley catheter needed)
8. Impaired hypoglycaemia awareness - autonomic symptoms of hypoglycaemia absent Management: Careful preloading, vasopressors ready (phenylephrine preferred), ECG monitoring, RSI for gastroparesis patients.

Long Viva Questions

• Investigations: HbA1c, FBS, electrolytes, creatinine/eGFR, ECG, lipid profile, urinalysis for microalbumin
• Medication management:
  • Empagliflozin (SGLT-2i): HOLD 72 hours before major surgery (euglycaemic DKA risk)
  • Metformin: Hold on morning of surgery (lactic acidosis risk)
  • Glipizide: Hold on morning of surgery (hypoglycaemia risk)
• If HbA1c ≥8.5%: Delay surgery, optimise glycaemic control
• Airway: Prayer Sign, neck mobility, Mallampati - longstanding DM → stiff joint syndrome possible
• Cardiovascular: Screen for autonomic neuropathy (orthostatic BP, HR variability), silent ischaemia
• Schedule as first morning case
• Consent: Explain increased risk of SSI, cardiac events

• Monitoring: ECG, SpO2, NIBP, capnography, temperature, blood glucose every 30-60 min
• Induction: Propofol (if no cardiovascular compromise) or etomidate (if haemodynamically compromised)
• Airway: RSI if gastroparesis present; videolaryngoscopy if stiff joint syndrome
• Maintenance: Volatile anaesthesia (sevoflurane preferred), opioid-sparing technique (reduces PONV and ileus)
• Fluids: Balanced crystalloid (Hartmann's); avoid large volumes of 0.9% NaCl (hyperchloraemic acidosis may mimic DKA)
• Glucose management: Target 140-180 mg/dL; VRII if insulin needed
• Vasopressors: Phenylephrine preferred over ephedrine

• PACU glucose monitoring: Every 1-2 hours
• Check urine/blood ketones (patient was on SGLT-2i - euglycaemic DKA risk even 72h after stopping)
• Resume medications only when eating normally and renal function confirmed
• Early enteral nutrition if surgery allows
• Analgesia: Multimodal (regular paracetamol, NSAIDs if renal function adequate, PCA opioids)
• DVT prophylaxis

• "What if this was emergency surgery and empagliflozin cannot be stopped?" → Proceed with RSI; check baseline ketones; monitor closely postoperatively; lower threshold to start insulin
• "How would your management differ for T1DM?" → Never omit basal insulin; higher risk of DKA; more intensive glucose monitoring; CSII pump patients - continue pump at basal rate

Common Examiner Cross-Questions

1. "What is the Whipple's triad?" (Symptoms of hypoglycaemia + glucose <3 mmol/L + relief with glucose - for diagnosing insulinoma)
2. "What is LADA?" (Latent Autoimmune Diabetes in Adults - T1DM presenting in adults, initially resembles T2DM, has autoantibodies)
3. "What is the ACCORD trial?" (Aggressive glucose control in T2DM with established CVD increased mortality - reinforces against very tight control)
4. "What is the Somogyi effect?" (Overnight hypoglycaemia triggers counter-regulatory hormone release → rebound morning hyperglycaemia - avoid by not over-insulinising at bedtime)
5. "What is the Dawn Phenomenon?" (Early morning hyperglycaemia due to physiological GH surge in early morning - treat by evening insulin dose adjustment)
6. "What is Charcot arthropathy?" (Neuropathic joint destruction in DM due to loss of protective sensation - affects ankle/foot - causes bony destruction, deformity - perioperative positioning important)

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16. MD THEORY EXAMINATION POINTS

Highly Probable University Questions

1. "Classify diabetes mellitus and discuss the anaesthetic management of a diabetic patient undergoing major surgery" - This is the most commonly repeated long essay in MD Anaesthesiology theory exams
2. "Discuss the perioperative management of a Type 1 diabetic patient"
3. "Write short notes on: (a) Diabetic Ketoacidosis and its anaesthetic management (b) SGLT-2 inhibitors and anaesthesia"
4. "What are the complications of diabetes mellitus relevant to anaesthesia? Discuss how you would assess and manage them"
5. "Discuss intraoperative glycaemic management in critically ill patients with reference to the NICE-SUGAR trial"

High-Yield Facts

• 5-10% of cases are T1DM; 90-95% are T2DM
• Delay elective surgery if HbA1c ≥8.5% (AAGBI); ≥9% (ADA Australia)
• Only Regular insulin is given IV - not rapid-acting analogues
• SGLT-2i: Hold 24h (minor) / 72h (major) before surgery → euglycaemic DKA
• GLP-1RA: Hold 24h (daily) / 7 days (weekly) before surgery → aspiration risk
• Metformin: Hold day of surgery → lactic acidosis
• Never omit all insulin in T1DM patients → DKA
• Target glucose perioperatively: 140-180 mg/dL
• NICE-SUGAR: Intensive control (80-110) → increased mortality; target 140-180 mg/dL in ICU
• Phenylephrine > Ephedrine in diabetics (ephedrine causes hyperglycaemia)
• Prayer Sign → stiff joint syndrome → predict difficult airway
• Potassium must be >3.5 mEq/L before starting insulin in DKA

Memory Aids and Mnemonics

"DIABETIC" - Anaesthetic Concerns

• D - Difficult airway (stiff joint syndrome)
• I - Ischaemic heart disease (silent)
• A - Autonomic neuropathy (haemodynamic instability)
• B - Blood glucose (tight but not too tight: 140-180)
• E - Euglycaemic DKA (SGLT-2i patients)
• T - Timing (first on morning list)
• I - Insulin (never omit in T1DM; adjust doses for T2DM)
• C - Cardiovascular + renal monitoring

"SGLT-2 = STOP Glucose" - Periop Rule

• Stop 7 days (weekly GLP-1RA)
• Stop 72 hours (major surgery SGLT-2i)
• Stop 24 hours (minor surgery SGLT-2i / daily GLP-1RA)
• Stop metformin day 0 (day of surgery)

"6 I's" of DKA Precipitants

DKA Management - "FRIED K"

• F - Fluids (0.9% NaCl first)
• R - Replace K+ (if <3.5, no insulin until corrected)
• I - Insulin (0.1 units/kg/hr IV Regular)
• E - Electrolytes (monitor hourly)
• D - Dextrose (add when glucose <250 mg/dL)
• K - Klue/Cause (identify precipitant)

Insulin Types Mnemonic - "RAP-LD" by Duration

Common Mistakes Made by Residents

1. Omitting all insulin in T1DM patients pre-operatively → precipitates DKA
2. Not checking potassium before starting insulin in DKA → life-threatening hypokalaemia
3. Stopping insulin infusion without overlap when transitioning to SC insulin → rebound hyperglycaemia
4. Targeting glucose <110 mg/dL in ICU → follows outdated Van den Berghe data, not NICE-SUGAR
5. Resuming metformin immediately postoperatively without confirming renal function
6. Not recognising euglycaemic DKA because glucose is normal in a SGLT-2i patient
7. Ignoring GLP-1RA gastroparesis risk and not performing RSI → aspiration
8. Using ephedrine as first-line vasopressor in diabetic hypotension
9. Forgetting stiff joint syndrome when assessing diabetic airway
10. Not correcting sodium for hyperglycaemia in HHS → underestimating true Na deficit

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17. CLINICAL PEARLS

OT (Operating Theatre) Pearls

1. "First on the morning list" rule is not just courtesy - it is a safety imperative. The longer a diabetic patient fasts, the higher the risk of hypoglycaemia (especially on sulfonylureas or insulin) and of metabolic derangement.
2. Insulin adsorbs to PVC IV tubing - flush the infusion set with 10-20 mL of insulin solution before connecting to patient to saturate binding sites, otherwise up to 30% of the dose is lost to tubing.
3. Warm patients before reversal - hypothermia impairs subcutaneous insulin absorption; on rewarming there can be a sudden surge of previously unabsorbed insulin → hypoglycaemia.
4. Dexamethasone hyperglycaemia: A single 8 mg dose of dexamethasone (used as antiemetic) causes blood glucose to peak at ~6 hours post-administration. Warn the receiving ward team. Monitor glucose 6-8 hours post-op when dex is given. (PMID: 39151134)
5. The "silent MI" trap: Diabetics can have a massive infarct with minimal or no symptoms - ST changes, haemodynamic collapse, or unexplained pulmonary oedema on the table may be the first sign. Have a low threshold for intraoperative 12-lead ECG and troponin.
6. Gastric ultrasound for GLP-1RA patients - If semaglutide was taken within 7 days of surgery, use point-of-care ultrasound to assess gastric contents before induction. A gastric antral cross-sectional area >340 mm² or the presence of solid/mixed gastric contents = full stomach → RSI.

ICU Pearls

1. "Permissive hyperglycaemia" in the ICU is NOT acceptable. While avoiding tight control (NICE-SUGAR lesson), glucose >180 mg/dL is still associated with adverse outcomes (SSI, AKI, delirium). Target 140-180 mg/dL actively.
2. Enteral nutrition is better than TPN for glycaemic control in ICU. The portal-first delivery of nutrients from EN results in more physiological insulin responses than TPN.
3. Never trust a glucose measurement from peripheral sites with poor perfusion (vasoconstriction, shock). Use arterial blood gas glucose measurement in haemodynamically unstable ICU patients - it is more reliable than capillary glucose.
4. Hypoglycaemia is the hidden killer in the ICU. A single episode of severe hypoglycaemia (<40 mg/dL) can cause irreversible neurological damage. The risk is heightened when: (a) insulin infusion is running, (b) nutritional support is interrupted, (c) renal function changes (reduced insulin clearance), (d) patient receives steroids and then they are weaned.

Practical Tips

1. "Dose adjustment for renal failure" applies to insulin too - insulin is partially cleared by the kidneys. In AKI/CKD, insulin half-life is prolonged → reduce doses and monitor more frequently.
2. In T1DM, NEVER omit all insulin perioperatively even if fasting. Without any insulin, T1DM patients will develop DKA within 4-8 hours. Give 50-80% of the basal dose. This is one of the most important and commonly tested points.
3. Type 2 DM patient requiring insulin post-op? If a T2DM patient who was previously on oral agents alone requires insulin in hospital, do NOT automatically assume they will need insulin permanently. Illness-induced insulin resistance often resolves. Reassess after discharge.
4. Continuous Glucose Monitoring (CGM/Flash) can be used perioperatively as an adjunct but must not replace capillary glucose checks during haemodynamically unstable periods. Position sensors away from surgical site, ECG leads, and electrosurgery path.

Pitfalls to Avoid

1. Do NOT use 5% dextrose as the routine IV fluid for diabetics - it will cause hyperglycaemia. Use balanced crystalloids (Hartmann's or PlasmaLyte) for maintenance. Add dextrose ONLY as part of a GIK/VRII protocol under controlled conditions.
2. Do NOT rely on signs and symptoms to diagnose hypoglycaemia in anaesthetised or sedated patients - autonomic symptoms (sweating, tremor, palpitations) are masked. The only reliable indicator is a blood glucose measurement. Monitor routinely.

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18. KEY TAKE-HOME MESSAGES

"The most important thing to remember in diabetic perioperative care is that the disease is in the complications, not the blood glucose alone." - Barash's Principle

1. Perioperative glucose target is 140-180 mg/dL - not <110 mg/dL (NICE-SUGAR: tight control kills in the ICU), not >200 mg/dL (SSI, impaired healing, organ damage)
2. SGLT-2 inhibitors must be stopped 24-72 hours before surgery to prevent euglycaemic DKA. Normal glucose does NOT exclude DKA in these patients - check ketones.
3. GLP-1 receptor agonists (especially weekly semaglutide) must be stopped 7 days before surgery to prevent gastroparesis-related aspiration. If not stopped: RSI and gastric ultrasound.
4. Never omit ALL insulin in Type 1 DM - even a fasting patient needs basal insulin (50-80% of dose) to prevent DKA.
5. The Prayer Sign predicts difficult airway in longstanding diabetics - examine every diabetic patient's hands, neck extension, and mouth opening preoperatively.
6. Cardiac autonomic neuropathy causes silent myocardial ischaemia - diabetic patients can have massive MIs without chest pain. Have a low threshold for ECG and troponin perioperatively.
7. Gastroparesis = full stomach - even if NPO for the prescribed time, a diabetic with autonomic neuropathy and gastroparesis should be treated as having a full stomach. Use RSI.
8. Phenylephrine is preferred over ephedrine as a vasopressor in diabetics because ephedrine's beta-adrenergic stimulation increases glucose via glycogenolysis.
9. K+ must be ≥3.5 mEq/L before starting insulin in DKA - insulin drives K+ intracellularly, precipitating life-threatening hypokalaemia if correction is not performed first.
10. Metformin hold perioperatively - resume only when eating and renal function is confirmed stable (24-48h post major surgery). The risk is lactic acidosis from hypoperfusion impairing lactate clearance.
11. HbA1c ≥8.5% → delay elective surgery (AAGBI). HbA1c ≥9% → delay (Australian DM Association). But HbA1c does not capture recent improvements; consider fructosamine for short-term monitoring.
12. The NICE-SUGAR trial definitively showed that intensive insulin therapy (80-110 mg/dL) increases ICU mortality. The current universal standard is 140-180 mg/dL.
13. Dexamethasone 8 mg IV (used as an antiemetic) causes transient hyperglycaemia peaking at 6 hours post-administration. Monitor glucose post-operatively.
14. DKA precipitants: "6 I's" - Infection (most common), Insulin omission, Ischaemia/Infarction, Intoxication, Iatrogenic (steroids), Inflammatory (pancreatitis).
15. In DKA, correct the sodium for hyperglycaemia - the measured hyponatraemia is dilutional (for every 100 mg/dL rise in glucose above 100 mg/dL, Na is diluted by ~1.6 mEq/L).
16. Insulin adsorbs to PVC tubing - flush IV tubing before connecting insulin infusion to avoid under-dosing.
17. Regional anaesthesia is often preferred in diabetics for major surgery - suppresses stress hyperglycaemia better than GA, allows sensorium monitoring, and reduces PONV (important in gastroparesis).
18. HHS (Hyperglycaemic Hyperosmolar State) carries 10-20% mortality - far higher than DKA. The profound dehydration (8-12 L deficit) and hypercoagulable state (DVT/stroke risk) require aggressive management. Do NOT drop glucose below 250-300 mg/dL rapidly.
19. Always calculate the Anion Gap in any diabetic with unexplained acidosis. If AG >12 with ketonaemia - DKA. If AG normal with ketonaemia - starvation ketosis or alcoholic ketoacidosis. AG >20 = severe, urgent intervention needed.
20. The diabetic patient's greatest perioperative killer is coronary artery disease, not blood glucose. Focus as much energy on cardiac risk stratification, beta-blocker continuation, statin therapy, and BP optimisation as on glycaemic management.

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References (Primary Sources Used)

• Miller's Anesthesia, 10th Edition (Gropper et al.), pp. 4219-4222 - Perioperative Management of Diabetes
• Barash's Clinical Anesthesia, 9th Edition (Barash et al.), Chapter 47 (Endocrine Function), pp. 4039-4053 - Diabetes Mellitus: Anesthetic Management, NICE-SUGAR, Table 47-11, Table 47-13
• Morgan & Mikhail's Clinical Anesthesiology, 7th Edition, Chapter 35, pp. 1408-1412 - Diabetes Mellitus: Classification, Acute Complications, Perioperative Care
• Harrison's Principles of Internal Medicine, 22nd Edition (2025, McGraw Hill) - Chapters 414-417: Approach to DM, Classification, Pharmacologic Treatment, Hypoglycaemia in Diabetes, HbA1c targets
• Recent Evidence: PMID 40814081 (2025 ADS/ANZCA GLP-1RA Guidelines), PMID 39151134 (Dexamethasone in Diabetics - Meta-Analysis), PMID 40613260 (Perioperative CGM - Systematic Review 2025)---

Session Summary

HYPERTENSION

Comprehensive MD Anaesthesiology Teaching Session

Sources: Miller's Anesthesia 10e | Barash's Clinical Anesthesia 9e | Morgan & Mikhail's Clinical Anesthesiology 7e | Harrison's Principles of Internal Medicine 22e | 2026 AAGBI/BIHS Guidelines (PMID 41532177) | 2025 ACEI/ARB Meta-Analysis (PMID 41017370)

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1. DEFINITION

Standard Textbook Definitions

Why the discrepancy matters for anaesthesia: The anaesthetist needs to know which definition the referring team used, and what the patient's usual/baseline BP is - not just the office measurement. The 2026 AAGBI/BIHS guideline specifically recommends basing decisions on ambulatory or home BP monitoring wherever possible.

Clinical Importance

• Most prevalent preoperative medical comorbidity in surgical patients: 20-25% of all surgical patients have hypertension (Morgan & Mikhail 7e)
• Hypertension is the leading global risk factor for cardiovascular death
• Perioperative hypertension is associated with increased risk of postoperative MI (OR 1.35; 95% CI 1.17-1.56) (Miller's 10e)
• LVH with strain pattern on ECG is an important predictor of perioperative cardiac mortality (Barash 9e)
• The anaesthetist's unique challenge: Maintaining haemodynamic stability in a patient whose regulatory mechanisms are chronically reset to operate at higher pressures

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2. INTRODUCTION

Background

Epidemiology

Relevance in Anaesthesia and Critical Care

1. Preoperative: Most common reason for surgery postponement; must risk-stratify for end-organ damage
2. Intraoperative: Exaggerated haemodynamic swings at induction and intubation; altered autoregulation; increased risk of ischaemia
3. Postoperative: Rebound hypertension after omitting antihypertensives; increased risk of MI, stroke, bleeding
4. ICU: Perioperative hypertensive crises; management of resistant hypertension; target BP after neurosurgery, vascular surgery, cardiac surgery
5. Drug interactions: Multiple antihypertensive-anaesthetic drug interactions requiring precise management

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3. BASIC SCIENCES

A. Physiology of Blood Pressure Regulation

The Fundamental Equation

Key Regulatory Systems

• Renin released from juxtaglomerular cells of the kidney in response to: decreased renal perfusion pressure, decreased Na+ delivery to macula densa, beta-adrenergic stimulation
• Renin cleaves angiotensinogen (liver) → Angiotensin I
• ACE (lung endothelium) converts Ang I → Angiotensin II
• Ang II effects:
  • Direct vasoconstriction (AT1 receptors on vessels) → increased TPR
  • Stimulates aldosterone secretion (adrenal cortex) → Na+/water retention → increased CO
  • Central thirst stimulation
  • Sympathetic potentiation
  • Renal tubular Na+ reabsorption (directly)
• RAAS is the primary chronic regulator of BP and volume

• Short-term, rapid BP regulation
• Norepinephrine → α1 receptors → vasoconstriction → increased TPR
• Norepinephrine → β1 receptors → increased HR and contractility → increased CO
• Epinephrine (adrenal medulla) → β2 > α1 at physiological levels
• Chronic SNS overactivity is a key mechanism in essential hypertension

• Arterial baroreceptors in carotid sinus (CN IX) and aortic arch (CN X)
• Detect stretch → inhibit medullary vasomotor centre → reduce SNS outflow
• In chronic hypertension: Baroreceptors are reset to a higher operating point - they "accept" high BP as normal and defend it
• Critical anaesthetic implication: Agents that blunt baroreflex (volatile anaesthetics, propofol) can cause precipitous hypotension; loss of this buffering mechanism also predisposes to hypertensive spikes with stimulation

• As BP rises → increased renal perfusion → natriuresis/diuresis → reduced volume → reduced CO
• The "infinite gain" mechanism - ultimately, only the kidney can set long-term BP
• Disrupted in CKD, high-salt diets, hyperaldosteronism

• Nitric Oxide (NO): Synthesised by eNOS from L-arginine in vascular endothelium → vascular smooth muscle relaxation → vasodilation. The most potent endogenous vasodilator
• Endothelin-1 (ET-1): Potent vasoconstrictor secreted by endothelium; acts on ETA receptors on vascular smooth muscle → sustained vasoconstriction
• Prostacyclin (PGI2): Vasodilator and platelet inhibitor from endothelium
• In hypertension: Decreased NO bioavailability + increased ET-1 → endothelial dysfunction → sustained vasoconstriction

• ANP (Atrial Natriuretic Peptide): Released from atria in response to stretch → natriuresis, vasodilation, inhibits RAAS/SNS
• BNP (Brain/B-type Natriuretic Peptide): Released from ventricles → same effects; used as biomarker of heart failure
• Impaired in chronic hypertension with LVH

B. Autoregulation of Cerebral Blood Flow - Critical Anaesthetic Concept

• CBF is maintained constant across a MAP range of 50-150 mmHg
• Below the Lower Limit of Autoregulation (LLA) (~MAP 50-60 mmHg): CBF falls (ischaemia)
• Above the upper limit (~MAP 150-160 mmHg): Breakthrough vasodilation, cerebral oedema (hypertensive encephalopathy)

• The entire autoregulation curve is shifted to the RIGHT
• LLA shifts from MAP ~50 to ~70-80 mmHg
• Upper limit also shifts - patients tolerate higher BP without oedema
• Critical implication: A "normal" MAP of 60 mmHg that is safe for a normotensive patient may be below the LLA for a chronically hypertensive patient → cerebral ischaemia

Landmark teaching from Miller's 10e (Neuroanaesthesia chapter): "Limiting the reduction in MAP to 30-35% from baseline seems appropriate" in hypertensive patients undergoing neurological procedures. A 25% reduction in MAP can bring both normotensive and hypertensive patients to the LLA.

• Long-term treatment partially restores the LLA toward normal
• ACE inhibitors shift the LLA left (toward lower pressures) acutely
• Restoration is incomplete even after 12 months in some patients (Miller's 10e)

C. Pathophysiology of Hypertension

Essential (Primary) Hypertension (~90-95% of cases)

• Abnormal renal sodium handling → expanded ECF volume → increased CO initially
• Autoregulation causes compensatory vasoconstriction → increased TPR
• Ultimately: high BP with high TPR (established hypertension)

• Increased renal sympathetic nerve activity → renin release, reduced natriuresis
• Augmented central sympathetic outflow (stress, obesity, OSA)
• Reduced baroreflex sensitivity

• Inappropriate RAAS activation despite volume expansion
• Aldosterone excess (primary or secondary)
• Angiotensin II-mediated vascular remodelling and oxidative stress

• Chronic pressure load → vascular hypertrophy → reduced lumen calibre → permanently elevated TPR
• Increased wall/lumen ratio
• Reduced vascular compliance → increased pulse wave velocity → isolated systolic hypertension in elderly

• Reduced NO production → impaired vasodilation
• Oxidative stress (superoxide inactivates NO)
• Impaired endothelium-dependent dilation

• Insulin promotes renal sodium retention and SNS activity
• Links hypertension to central obesity, dyslipidaemia, T2DM (metabolic syndrome)

• Heritability ~40-60%
• Polygenic: variants in genes for RAAS (ACE, AGT), sodium transporters (SLC12A3/Gitelman), endothelin, adrenergic receptors
• Rare monogenic forms (Liddle syndrome, Gordon syndrome) - high yield for viva

Viva Point: "What is Liddle Syndrome?" - Autosomal dominant gain-of-function mutation in epithelial sodium channel (ENaC) subunits → constitutively open channel → excessive Na+ reabsorption in cortical collecting duct → hypertension, hypokalaemia, metabolic alkalosis, LOW renin, LOW aldosterone. Treated with amiloride or triamterene (ENaC blockers), NOT spironolactone.

Secondary Hypertension (~5-10% of cases)

Anaesthetic Pearl: Phaeochromocytoma must be excluded before any surgery in a patient with paroxysmal hypertension + tachycardia + headache + diaphoresis. Undiagnosed phaeochromocytoma is one of the most dangerous anaesthetic situations - induction can trigger a hypertensive crisis and death.

Hypertensive Target Organ Damage

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4. CLASSIFICATION

A. ACC/AHA 2017 Classification (Used by Morgan & Mikhail, Barash)

B. ISH/ESC/ESH 2020/2023 Classification (Traditional - Widely Used in India)

C. Hypertensive Crisis Classification

• Brain: Hypertensive encephalopathy, haemorrhagic/ischaemic stroke, PRES
• Heart: Acute MI, acute pulmonary oedema, acute aortic dissection
• Kidney: Acute hypertensive nephrosclerosis (thrombotic microangiopathy)
• Eye: Papilloedema (Grade IV retinopathy)
• Obstetric: Eclampsia

HIGH-YIELD VIVA: "What is PRES?" - Posterior Reversible Encephalopathy Syndrome. Hypertension → failure of posterior cerebral autoregulation → vasogenic oedema in parieto-occipital regions. MRI: T2/FLAIR hyperintensity (white matter oedema) in posterior regions. Features: seizures, visual disturbances, encephalopathy, headache. Treatment: controlled BP reduction, seizure management. Reversible with BP control.

D. Based on Aetiology

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5. ETIOLOGY AND RISK FACTORS

Risk Factors for Essential Hypertension

Risk Stratification for Cardiovascular Events

1. LVH (ECG strain pattern or echo-confirmed) - most important predictor of perioperative cardiac mortality
2. Prior MI or revascularisation
3. Stroke or TIA history
4. CKD (eGFR <60 mL/min or proteinuria)
5. Diabetes mellitus
6. Age >65 years
7. Active smoker

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6. CLINICAL FEATURES

Symptoms

• Headache (classically occipital, present on waking - from cerebral oedema due to loss of nocturnal BP dipping)
• Epistaxis
• Visual disturbance (blurred vision, scotoma - from retinopathy)
• Nausea and vomiting (raised ICP in hypertensive encephalopathy)

• Chest pain, dyspnoea, orthopnoea (IHD, HF)
• Palpitations, syncope (arrhythmia - from LVH)
• Haematuria, frothy urine (nephropathy)
• Focal neurological deficits (stroke)
• Leg claudication (peripheral arterial disease)
• Neck pain, tearing back pain (aortic dissection - EMERGENCY)

Signs

General/Cardiovascular Examination

• BP elevated: Measure in both arms - difference >15 mmHg SBP suggests subclavian stenosis or aortic coarctation
• Pulse: May show bounding character (wide pulse pressure), slow-rising (aortic stenosis complication)
• JVP elevated (if CCF has developed)
• Apex beat displaced (left ventricular enlargement/hypertrophy)
• S4 (4th heart sound): Low-pitched, presystolic - classic sign of LVH and diastolic dysfunction - "atrial gallop" heard best with bell at apex
• Renal artery bruit (epigastric/flank): Suggests renovascular hypertension

Eye Examination (Keith-Wagener-Barker Grading of Hypertensive Retinopathy)

Exam Point: Grade III and IV retinopathy are associated with hypertensive emergency and mandate immediate IV antihypertensive therapy. Finding papilloedema preoperatively requires postponing surgery.

Features Suggesting Secondary Hypertension on Examination

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7. DIAGNOSIS

Accurate Blood Pressure Measurement - Critical Skill

1. Patient seated, arm at heart level, back supported, legs uncrossed
2. Rest quietly for 5 minutes before measurement
3. Appropriate cuff size: Bladder length 80% and width 40% of arm circumference; a small cuff on a large arm gives falsely high reading
4. Average of 2+ readings, on 2+ occasions for diagnosis
5. Measure in both arms at first visit
6. Avoid caffeine, exercise, smoking for 30 minutes before

• Office/Clinic BP: Most widely used; highest; affected by white-coat effect
• ABPM (Ambulatory BP Monitoring - 24h): Gold standard; most predictive of outcomes; free of white-coat effect; identifies nocturnal non-dipping
• HBPM (Home BP Monitoring): Second best; practical; empowers patient self-management

Investigations

Mandatory for ALL Hypertensive Patients (Preoperatively)

Selective (Directed by Clinical Suspicion)

ECG Criteria for LVH

Exam Point: LVH strain pattern on ECG suggests chronic ischaemic state and is an important predictor of perioperative cardiac mortality (Barash 9e). These patients require more careful haemodynamic management.

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8. MANAGEMENT

A. Non-Pharmacological (Lifestyle) Interventions

B. Pharmacological Management

Drug Selection Principles (First-line Agents for Uncomplicated HTN)

1. Thiazide diuretics (chlorthalidone, hydrochlorothiazide, indapamide)
2. ACE inhibitors (ramipril, enalapril, perindopril, lisinopril)
3. Angiotensin Receptor Blockers/ARBs (losartan, telmisartan, valsartan)
4. Calcium Channel Blockers/CCBs (amlodipine, nifedipine - dihydropyridine; diltiazem, verapamil - non-dihydropyridine)
5. Beta-blockers (atenolol, metoprolol, bisoprolol, carvedilol, labetalol) - second-line for uncomplicated HTN; first-line with IHD, HF, post-MI

Compelling Indications for Specific Drug Classes

CRITICAL EXAM POINT: In phaeochromocytoma, alpha blockade MUST precede beta blockade. If a beta-blocker is given first (before alpha blockade), unopposed alpha-adrenergic vasoconstriction from circulating catecholamines causes a hypertensive crisis. The order is always: phenoxybenzamine (or prazosin) first → achieve adequate alpha blockade for 7-14 days → THEN add propranolol (beta-blocker) to control tachycardia.

Treatment Targets (Harrison's 22e / ACC/AHA 2017)

C. Management of Hypertensive Emergency

IV Drugs for Hypertensive Emergency

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9. ANAESTHETIC CONSIDERATIONS

A. Preoperative Assessment and Optimisation

History (Hypertension-Focused)

1. Duration and severity of hypertension
2. Current antihypertensive medications and compliance
3. Home BP diary readings (more reliable than one-off clinic reading)
4. History of end-organ damage: chest pain, dyspnoea, TIA/stroke, renal disease
5. Symptoms suggesting secondary hypertension (paroxysmal attacks, OSA, Cushing's features)
6. History of previous haemodynamic instability under anaesthesia
7. Concurrent risk factors: smoking, diabetes, dyslipidaemia

Physical Examination

• BP in both arms (BP difference >15 mmHg - investigate)
• BP supine and standing (assess orthostatic hypotension - especially on diuretics, alpha-blockers)
• Heart rate and rhythm
• Apex beat position and character
• Auscultation: S4, murmurs, basal crepitations
• Optic fundi (if possible)
• Peripheral pulses and bruits
• Signs of fluid overload or volume depletion

The Key Perioperative Decision: To Postpone or Proceed?

• Systolic BP <180 mmHg and diastolic BP <110 mmHg: NOT associated with increased perioperative risk on its own
• Therefore: Proceed with elective surgery if BP <180/110 mmHg

• Secondary care perioperative teams should accept referrals if:
  • Clinic BP <160/100 mmHg OR
  • Ambulatory/home BP <155/95 mmHg in past 12 months
• If patient attends pre-assessment without documented normotension from GP, they may proceed to elective surgery if:
  • Clinic BP <180/120 mmHg OR
  • Home BP <175/115 mmHg
• Postpone if: BP ≥180/120 mmHg (hypertensive crisis) at pre-assessment, especially if end-organ damage signs present

• Delay elective surgery if SBP >180 mmHg or DBP >110 mmHg
• NO benefit to delay has been proven for BP below this threshold

• Is there end-organ damage (LVH strain, retinopathy grade III/IV, creatinine elevation, proteinuria)?
• Is surgery urgent or time-critical?
• Is the elevated BP likely situational (white-coat effect, pain, anxiety)?
• Have antihypertensive medications been taken today?

HIGH-YIELD EXAM POINT: "Systolic blood pressures below 180 mm Hg and diastolic pressures below 110 mm Hg have not been associated with increased perioperative risks." (Morgan & Mikhail 7e, p.713). This is the single most important threshold to know.

Preoperative Antihypertensive Medication Management

The ACEi/ARB Controversy - Critical Exam Topic

• ACEi/ARBs block the RAAS - the body's primary defence against anaesthesia-induced hypotension
• Under general anaesthesia, CO falls + SVR falls → RAAS activation is the compensatory response
• ACEi/ARBs blunt this response → severe, refractory intraoperative hypotension (vasoplegic shock)
• This hypotension is often refractory to vasopressors (phenylephrine, ephedrine) and may require vasopressin
• Miller's 10e: "Administration of these medications within 24 hours before surgery is associated with increased risks of intraoperative hypotension"

• Abrupt discontinuation → rebound hypertension postoperatively (rebound RAAS activation)
• Failure to resume ACEi/ARBs postoperatively associated with adverse cardiovascular outcomes (Miller's 10e)
• May be cardioprotective (anti-ischaemic, antiremodelling)

• Withholding reduced intraoperative hypotension (36.4% vs 48.4%; RR=0.73, p=0.001)
• Withholding reduced vasopressor use (37.5% vs 51.2%)
• Withholding increased postoperative hypertension (27.8% vs 20.2%)
• No difference in MACE, AKI, mortality
• Evidence certainty: Very low (GRADE)

• Withhold ACEi/ARB for 24h before surgery (most anaesthetic guidelines including Miller's, 2026 AAGBI/BIHS)
• Restart as soon as patient is haemodynamically stable postoperatively (typically within 24-48h)
• Exception: Continue if patient has specific indications where the drug is critical (HFrEF, post-MI, CKD with proteinuria) - weigh risks carefully
• If ACEi/ARB was continued: warn the surgical team; have vasopressin available; treat with vasopressin 1-2 units IV bolus for refractory hypotension

Critical Exam Point: "Failure to resume ACEI and ARB therapy postoperatively is itself associated with adverse outcomes." (Miller's 10e). Withholding is a bridge strategy, not permanent cessation.

B. Induction of Anaesthesia

"Regardless of the level of preoperative blood pressure control, many patients with hypertension display an accentuated hypotensive response to induction of anaesthesia, followed by an exaggerated hypertensive response to intubation." (Morgan & Mikhail 7e)

• Phase 1 - Hypotension:
  • Anaesthetic agents cause vasodilation and myocardial depression
  • Volume depletion (from chronic diuretic use, poor oral intake)
  • Loss of sympathetic tone (sympatholytic agents)
  • Blunted baroreflex (resetting in chronic HTN)
• Phase 2 - Hypertension (laryngoscopy/intubation):
  • Laryngoscopy stimulates SNS → massive catecholamine release
  • Exaggerated response in hypertensives due to reset autoregulation and hyperresponsive SNS
  • Peak at 30-60 seconds after laryngoscopy; resolves within 5 minutes
  • Most dangerous in patients with IHD, aortic aneurysm, LVH

Strategies to Attenuate Pressor Response to Laryngoscopy

Induction Agents

C. Maintenance of Anaesthesia

• Maintain within 20% of preoperative baseline (Morgan & Mikhail 7e)
• For chronic hypertensives: do NOT target "normal" BP (MAP 65-70 mmHg) - this may be below their shifted LLA
• Aim for MAP 70-90 mmHg (or patient-specific baseline)
• For neurosurgery: limit MAP reduction to ≤30-35% from baseline (Miller's Neuroanaesthesia)

Volatile Agents

• All volatile agents (sevoflurane, isoflurane, desflurane) cause dose-dependent vasodilation and cardiac depression → reduce BP
• Desflurane can cause a sympathetic surge on rapid concentration increases → acute hypertension and tachycardia - avoid rapid increase in CVS-compromised patients
• At 1-1.5 MAC, most volatiles adequately control hypertension from routine surgical stimulation

Regional Anaesthesia Considerations

• Neuraxial blockade (spinal/epidural): More profound hypotension in hypertensives due to:
  • High baseline SNS tone - when blocked, BP drops significantly
  • Volume depletion (diuretics)
  • Blunted compensatory responses (ACEi/ARBs)
• Ensure adequate preloading before neuraxial block
• Have vasopressors immediately available (phenylephrine 50-100 mcg boluses or ephedrine 6 mg boluses for bradycardia)
• Epidural anaesthesia preferable to single-shot spinal for major procedures (more controllable block level and haemodynamics)

Monitoring

• Standard: ECG (ST analysis - lead II + V5), SpO2, NIBP, capnography, temperature
• Invasive arterial monitoring (A-line): For:
  • Wide BP swings expected
  • Major vascular or cardiac surgery
  • Severe/uncontrolled hypertension
  • Patients on multiple antihypertensives
  • Need for frequent ABG
• Urinary catheter: If renal impairment + procedure >2 hours
• TEE or TTE: If suspected diastolic dysfunction or severe LVH

Intraoperative Hypertension - Management

1. Insufficient anaesthetic depth (most common - check ETAA, TOF, BIS)
2. Surgical stimulus without adequate analgesia
3. Intubation/airway stimulation - pressor response
4. Bladder distension (autonomic stimulus)
5. Hypoxia or hypercarbia (adrenergic surge)
6. Inadequate antiemetic (nausea → Valsalva)
7. Rebound from omitted antihypertensives
8. Phaeochromocytoma (must be in differential for unexplained severe intraoperative hypertension)
9. Aortic cross-clamping
10. Malignant hyperthermia (late sign)
11. Elevated ICP
12. Drug interactions (e.g., ketamine given without adequate depth)

1. Rule out and treat correctable causes (deepen anaesthesia, analgesia, check airway)
2. Labetalol 5-20 mg IV (alpha + beta blockade; ideal for most situations)
3. Esmolol 0.5-1 mg/kg bolus (rapid beta blockade for tachycardia + hypertension)
4. GTN/Nitroglycerin 100-200 mcg IV bolus (primarily venodilator; useful in IHD)
5. Nicardipine 1-2 mg IV bolus (CCB; arterial dilation; excellent for neurosurgery)
6. Hydralazine 5-10 mg IV (slow onset 10-20 min; unpredictable; use cautiously)
7. Sodium nitroprusside infusion (for severe refractory hypertension; rapid, titratable)
8. Phentolamine 2-5 mg IV (if phaeochromocytoma suspected)

Intraoperative Hypotension - Management

1. Vasopressors:
   • Phenylephrine 50-100 mcg IV bolus (pure alpha-1 agonist; increases SVR; preferred when BP low without bradycardia)
   • Ephedrine 6 mg IV bolus (mixed alpha/beta; increases HR + BP; useful when bradycardia present)
   • Vasopressin 0.5-2 units IV bolus (for refractory vasodilation especially after ACEi/ARBs; acts on V1 receptors independent of RAAS)
   • Norepinephrine infusion (0.01-0.5 mcg/kg/min) for sustained hypotension
2. Intravenous fluid bolus (250-500 mL balanced crystalloid) if hypovolaemic
3. Reduce anaesthetic depth if appropriate

D. Postoperative Care

Causes of Postoperative Hypertension (Miller's 10e - Cardiac Surgery ICU)

1. Pain and anxiety (most common)
2. Withdrawal of antihypertensives (rebound RAAS/SNS)
3. Hypothermia → vasoconstriction → increased TPR
4. Hypoxia or hypercarbia → sympathetic activation
5. Bladder distension
6. Fluid overload
7. Emergence agitation
8. Nausea → Valsalva → increased BP

• Increased myocardial work + O2 demand → MI
• Cardiac rhythm disturbances
• Cerebrovascular accidents (stroke)
• Bleeding from anastomoses or surgical sites
• Suture line disruption (carotid, aortic, intracranial anastomoses)
• Impaired wound healing

• Treat correctable causes first (pain, hypothermia, bladder)
• Resume preoperative antihypertensives as soon as patient is taking orally
• IV labetalol, esmolol, nicardipine, or GTN for acute control
• Restart ACEi/ARBs within 24-48h once haemodynamically stable

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10. DRUGS

A. BETA-BLOCKERS (Perioperatively Critical)

POISE Trial Warning: In POISE-1, high-dose metoprolol started the night before surgery in beta-blocker naive patients reduced MI but increased stroke and overall mortality. Conclusion: Chronic beta-blockers should be continued; DO NOT START high-dose beta-blockers acutely before surgery in beta-blocker naive patients.

B. ACE INHIBITORS

Airway Emergency with ACEi: ACEi-induced angioedema can cause life-threatening airway obstruction. Features: non-pitting oedema of lips, tongue, larynx; no urticaria (unlike anaphylaxis). Treatment: adrenaline + C1-inhibitor concentrate (Berinert) + fresh frozen plasma + icatibant (bradykinin B2 antagonist). Does NOT respond to adrenaline alone as reliably as IgE-mediated anaphylaxis.

C. ANGIOTENSIN RECEPTOR BLOCKERS (ARBs)

D. CALCIUM CHANNEL BLOCKERS (CCBs)

E. SODIUM NITROPRUSSIDE (SNP)

F. HYDRALAZINE

G. CLONIDINE (Alpha-2 Agonist)

H. GLYCERYL TRINITRATE (GTN/Nitroglycerin)

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11. SCORES, FORMULAE, AND NUMERICAL VALUES

Key BP Numerical Values

Important Formulae

1. Mean Arterial Pressure (MAP)

2. Pulse Pressure (PP)

• Increased PP (>60 mmHg): Aortic regurgitation, aortic stiffness (elderly hypertension), hyperthyroidism, severe anaemia
• Decreased PP (<25 mmHg): Cardiac tamponade, severe aortic stenosis, cardiogenic shock

3. Cerebral Perfusion Pressure (CPP)

• Critical in neurosurgery: Hypertensive patients already have elevated MAP → must account for possible elevated ICP
• Antihypertensive overdose in a hypertensive patient with raised ICP → CPP below threshold → ischaemia

4. Rate-Pressure Product (RPP) - Myocardial O2 Demand

• RPP is a surrogate for myocardial O2 demand
• In hypertensive patients: elevated SBP + tachycardia → very high RPP → high ischaemia risk
• Target: RPP <12,000 intraoperatively in at-risk patients

5. The 20% Rule for Intraoperative BP Management

• Maintain BP within 20% of preoperative baseline MAP
• Example: Preoperative MAP = 110 mmHg → maintain MAP ≥88 mmHg; avoid exceeding 132 mmHg

Scoring Systems

Revised Cardiac Risk Index (RCRI/Lee Index)

Keith-Wagener-Barker Grading (Hypertensive Retinopathy)

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12. GUIDELINES

1. 2026 AAGBI/BIHS Updated Guidelines - Most Current (PMID: 41532177)

• Accept referrals if clinic BP <160/100 mmHg or home/ABPM <155/95 mmHg (documented in past 12 months)
• If no prior BP documentation: proceed if clinic BP <180/120 mmHg or home BP <175/115 mmHg
• Covers adults having planned surgery (excludes cardiothoracic, obstetric, endocrine)
• Covers perioperative period: decision to operate → 30 days post-surgery
• Emphasises home/ambulatory BP over single clinic measurement
• Stresses communication between primary care, surgical team, and patient

2. ACC/AHA 2017 Guideline for High Blood Pressure

• Redefines hypertension as ≥130/80 mmHg
• First-line: lifestyle + thiazide/ACEi/ARB/CCB
• Target <130/80 mmHg for most adults
• Beta-blockers: second-line for uncomplicated HTN (preferred with IHD, HF, post-MI)

3. ESC/ESH 2023 Guidelines

• Maintain ISH/traditional threshold of 140/90 mmHg for diagnosis
• Target <140/90 mmHg (general); <130/80 mmHg if tolerated in younger patients
• Out-of-office BP (ABPM/HBPM) recommended to confirm diagnosis

4. ISH 2020 Global Hypertension Practice Guidelines

• "Essential" target <130/80 mmHg (ideal); minimum target <140/90 mmHg (basic)
• Applicable to resource-limited settings globally
• Emphasises thiazide, CCB, ACEi/ARB as first-line

5. POISE Trial (2008) - Beta-Blockers

• 8,351 beta-blocker naive patients randomised to high-dose metoprolol vs placebo starting night before surgery
• Metoprolol: reduced MI (4.2% vs 5.7%) but increased stroke (1.0% vs 0.5%) and total mortality (3.1% vs 2.3%)
• Conclusion: Do NOT start high-dose beta-blockers acutely before surgery in naive patients. Continue pre-existing therapy.

6. SPRINT Trial (2015)

• 9,361 adults with SBP ≥130 mmHg + cardiovascular risk
• Intensive target (SBP <120 mmHg) vs standard (SBP <140 mmHg)
• Intensive group: 25% reduction in cardiovascular events; 27% reduction in mortality
• But: More adverse events (hypotension, syncope, AKI, electrolyte disturbances)
• Note: SPRINT excluded diabetics, stroke patients - results not universally applicable

7. 2025 ACEI/ARB Meta-Analysis (PMID: 41017370) - New Evidence

• 14 RCTs, 4,063 patients
• Withholding vs continuing ACEi/ARBs before noncardiac surgery
• Withholding reduces intraoperative hypotension (36.4% vs 48.4%) and vasopressor use
• But increases postoperative hypertension
• No mortality, MACE, or AKI difference
• Evidence certainty: very low - no definitive recommendation possible yet

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13. IMPORTANT TABLES

Table 1: Antihypertensive Drug Perioperative Management Summary

Table 2: Comparison of IV Antihypertensives for Perioperative Use

Table 3: Causes of Intraoperative Hypertension - Mnemonic "PHASED"

Table 4: Secondary Hypertension - Diagnostic Summary

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14. FLOWCHARTS AND ALGORITHMS

Algorithm 1: Preoperative Assessment of Hypertensive Patient

PATIENT WITH KNOWN/SUSPECTED HYPERTENSION
               ↓
ACCURATE BP MEASUREMENT
(Bilateral arms; seated x5 min rest)
               ↓
      BP <160/100 mmHg?           (2026 AAGBI threshold for GP referral acceptance)
       /              \
     YES               NO
      ↓                 ↓
  Assess            Is BP <180/120 mmHg?
  end-organ          /             \
  damage           YES              NO
      ↓              ↓               ↓
      ↓           Proceed        POSTPONE
      ↓           (no prior     elective surgery
      ↓          documented     Treat and
      ↓           normal BP)    re-evaluate
      ↓
IS THERE END-ORGAN DAMAGE?
  (LVH strain, retinopathy III/IV, CKD, prior MI/stroke)
       /              \
     YES               NO
      ↓                 ↓
  Cardiology         Proceed if
  referral           BP <180/110 mmHg
  Optimise           (traditional threshold)
      ↓
MEDICATION REVIEW
  Hold ACEi/ARBs 24h
  Continue beta-blockers
  Continue clonidine
  Check K+ if on diuretics
               ↓
  SCHEDULE AS FIRST MORNING CASE
  (fasting minimised; less situational hypertension)

Algorithm 2: Management of Pressor Response to Laryngoscopy

HYPERTENSIVE PATIENT REQUIRES INTUBATION
               ↓
PRE-INDUCTION PREPARATION
  - Optimise depth of anaesthesia (MAC >1.3)
  - Pre-treat with chosen technique:
               ↓
    Choose ONE or COMBINATION:
    ┌──────────────────────────────────────────────┐
    │ Opioid: Fentanyl 2.5-5 mcg/kg (3 min before)│
    │ Lignocaine: 1.5 mg/kg IV (3 min before)      │
    │ Esmolol: 0.5-1.5 mg/kg IV (2 min before)     │
    │ Labetalol: 5-20 mg IV (5-10 min before)      │
    │ Dexmedetomidine: 0.5-1 mcg/kg over 10 min    │
    └──────────────────────────────────────────────┘
               ↓
   LARYNGOSCOPY → INTUBATE EXPEDITIOUSLY
   (< 15 seconds if possible; video laryngoscope)
               ↓
    BP/HR RESPONSE MONITORED
       /                   \
   Acceptable          BP/HR rise >20% from baseline
      ↓                       ↓
  Continue                IMMEDIATE TREATMENT:
  monitoring              1. Deepen anaesthesia
                          2. Esmolol 0.5 mg/kg IV
                          3. Nicardipine 1-2 mg IV
                          4. GTN 100 mcg IV bolus
                          5. Consider sodium
                             nitroprusside infusion

Algorithm 3: Intraoperative Hypotension in Hypertensive Patient on ACEi/ARBs

INTRAOPERATIVE HYPOTENSION (MAP <65 mmHg or >20% decrease)
               ↓
    Is patient on ACEi/ARBs? (taken within 24h)
         /               \
       YES                NO
        ↓                  ↓
REFRACTORY            Standard vasopressors
VASODILATION          (Phenylephrine 50-100 mcg IV)
        ↓
FIRST: Rule out surgical bleeding, pneumothorax
        ↓
IV Fluid bolus 250-500 mL
        ↓
Phenylephrine/Ephedrine - may be INADEQUATE
        ↓
VASOPRESSIN 1-2 units IV bolus (RAAS-independent)
   → Most effective for ACEi/ARB-associated hypotension
        ↓
Vasopressin infusion 0.03-0.04 units/min if needed
        ↓
Norepinephrine infusion 0.05-0.5 mcg/kg/min
        ↓
Consider: Methylene blue (severe vasoplegic shock)
   - 1.5-2 mg/kg IV over 20 min
   - Inhibits guanylyl cyclase → reduces NO effect

Algorithm 4: Management of Hypertensive Emergency

BP >180/120 + SIGNS OF END-ORGAN DAMAGE
               ↓
    IMMEDIATE IV ACCESS + MONITORING
    (ICU/HDU; invasive arterial line; ECG; urine output)
               ↓
    IDENTIFY THE ORGAN AT RISK:
    ┌────────────────────────────────────────────────┐
    │ Neurological: Stroke/PRES/Encephalopathy       │
    │ Cardiac: ACS/Aortic Dissection/Acute HF        │
    │ Renal: Thrombotic microangiopathy              │
    │ Obstetric: Eclampsia                           │
    └────────────────────────────────────────────────┘
               ↓
    TARGET: Reduce MAP by MAX 25% in FIRST HOUR
    (Exception: Aortic dissection - reduce SBP to
    <120 mmHg within 20 min)
               ↓
    CHOOSE AGENT BASED ON ORGAN AT RISK:
    • Neurological: Nicardipine or Labetalol
    • Cardiac/IHD: Nitroglycerin ± Labetalol
    • Aortic dissection: Esmolol + Nitroprusside
    • Acute HF/Pulm oedema: Nitroglycerin + Furosemide
    • Eclampsia: IV Labetalol or Hydralazine + MgSO4
    • Phaeochromocytoma: Phentolamine
               ↓
    HOURS 2-6: Reduce to 160/100 mmHg
               ↓
    HOURS 6-24: Gradually normalise
               ↓
    TRANSITION to oral antihypertensives

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15. FREQUENTLY ASKED MD VIVA QUESTIONS

Short Viva Questions

Long Viva Questions

• This BP (170/105) is Grade 2/Stage 2 but below the 180/110 threshold → proceed with surgery (no absolute contraindication)
• Investigations: ECG (LVH? Strain pattern?), electrolytes (K+ with diuretics?), creatinine/eGFR, urinalysis, blood glucose, lipid profile, echocardiography if LVH on ECG
• Medication: Continue atenolol (morning of surgery); Continue amlodipine; Hold ramipril 24h before (ACEi - hypotension risk)
• Remind patient to take atenolol and amlodipine with sip of water on morning of surgery
• Ensure adequate hydration preoperatively

• Monitoring: ECG with ST analysis (lead II + V5), SpO2, NIBP, capnography; consider invasive arterial monitoring given labile BP history and major abdominal surgery
• Urinary catheter (major surgery >2h, renal risk assessment)
• Maintain MAP within 20% of preoperative baseline (baseline MAP = 127 mmHg; maintain ≥100 mmHg)
• Induction: Propofol slowly titrated (risk of hypotension - volume depleted, on antihypertensives); consider etomidate if haemodynamically unstable; pre-treat with fentanyl 3-4 mcg/kg + lignocaine 1.5 mg/kg before intubation to blunt pressor response
• Airway: Standard RSI for abdominal surgery; video laryngoscopy available
• Maintenance: Sevoflurane-based; multimodal analgesia (epidural if appropriate) - reduces stress response
• Fluids: Balanced crystalloid (Hartmann's); goal-directed fluid therapy with cardiac output monitoring
• Vasopressors: Phenylephrine infusion ready; vasopressin available (because ramipril was held but residual effect may persist if taken in last 24-48h)

• Continue ECG monitoring; neurological assessment
• Restart amlodipine and atenolol as soon as taking orally
• Restart ramipril within 24-48h once haemodynamically stable
• Monitor for: rebound hypertension (pain, atenolol withdrawal), hypotension (volume shifts post-surgery), AKI (major surgery + ACEi interaction)
• Adequate multimodal analgesia (pain → hypertension → myocardial stress)
• Wound care: HTN patients → higher bleeding risk, slower wound healing

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16. MD THEORY EXAMINATION POINTS

Highly Probable University Questions

1. "Discuss the anaesthetic management of a patient with uncontrolled hypertension scheduled for elective surgery" - Most commonly repeated long essay
2. "What is hypertensive emergency? Describe its management with reference to specific organ systems"
3. "Discuss the intraoperative haemodynamic changes in hypertensive patients and their management"
4. "Write short notes on: (a) Pressor response to laryngoscopy and its attenuation (b) ACE inhibitors in perioperative medicine"
5. "Discuss the pharmacology of sodium nitroprusside with its anaesthetic relevance"
6. "What are the perioperative implications of antihypertensive drugs?"

High-Yield Exam Facts

• Most prevalent preoperative medical comorbidity: Hypertension (20-25% of surgical patients)
• BP threshold for elective surgery postponement: SBP >180 or DBP >110 mmHg (traditional); clinic BP ≥180/120 (AAGBI 2026)
• BP <180/110 = No increased perioperative risk on its own
• Autoregulation shift: Rightward in chronic HTN; LLA at MAP ~70-80 mmHg (vs normal ~50 mmHg)
• Safe MAP reduction: ≤20-25% from baseline (general surgery); ≤30-35% (neurosurgery)
• Hold ACEi/ARBs 24h before surgery; restart as soon as haemodynamically stable
• Never stop beta-blockers or clonidine abruptly perioperatively
• Pressor response peak: 30-60 seconds after laryngoscopy
• Best attenuation: Fentanyl 2.5-5 mcg/kg + Esmolol or Labetalol
• Refractory hypotension with ACEi/ARBs: Vasopressin 1-2 units IV
• SNP toxicity: Cyanide → lactic acidosis (acute); thiocyanate → neurotoxicity (chronic/renal failure)
• Hypertensive emergency: Lower MAP by max 25% in FIRST hour
• Phaeochromocytoma rule: Alpha blockade FIRST, then beta blocker
• POISE trial: Acute high-dose beta blocker perioperatively → increased stroke and mortality
• S4 heart sound: Hallmark of LVH + diastolic dysfunction in hypertensive patient
• Keith-Wagener Grade IV (papilloedema): Hypertensive emergency; postpone any elective surgery

Memory Aids and Mnemonics

"ABCDE" of Hypertensive Perioperative Management

• A - Assess end-organ damage (ECG, creatinine, urinalysis, fundoscopy)
• B - Beta-blockers: CONTINUE; Beware of holding ACEi/ARBs (hold 24h)
• C - Cerebral autoregulation shifted Right → maintain baseline MAP within 20%
• D - Dangerously exaggerated Dual response (hypotension at induction, hypertension at intubation)
• E - Emergency drugs ready: Esmolol, vasopressin, nicardipine, nitroprusside

Drugs to NEVER STOP Abruptly (mnemonic "BC")

• Beta-blockers → rebound tachycardia, MI
• Clonidine → rebound hypertensive crisis

Causes of Intraoperative Hypertension: "PHASED"

"SNP = Seven Nasty Problems"

Alpha BEFORE Beta in Phaeochromocytoma: "A before B, as in the Alphabet"

• A (Alpha) blockade first: phenoxybenzamine 7-14 days
• B (Beta) blocker after: propranolol for tachycardia control

Common Mistakes Made by Residents

1. Cancelling surgery for BP of 160/100 mmHg - not evidence-based; threshold is 180/110 (or 180/120 per 2026 AAGBI)
2. Targeting MAP 65 mmHg intraoperatively in a hypertensive patient - this may be below their shifted LLA → cerebral ischaemia
3. Stopping beta-blockers before surgery "to avoid bradycardia" → rebound tachycardia and MI
4. Giving beta-blocker before alpha-blocker in suspected phaeochromocytoma → hypertensive crisis
5. Treating refractory ACEi/ARB hypotension with increasing doses of phenylephrine alone → ineffective; give vasopressin
6. Using SNP in neurosurgical patients without understanding it raises ICP (cerebral vasodilation → increased CBV)
7. Not restarting ACEi/ARBs postoperatively → rebound hypertension and adverse cardiovascular outcomes
8. Treating white-coat hypertension as true hypertension - check ABPM/home BP
9. Missing signs of secondary hypertension - especially phaeochromocytoma (paroxysmal symptoms) and Conn's (unprovoked hypokalaemia)
10. Forgetting S4 significance - indicates diastolic dysfunction → these patients are preload-dependent and tolerate hypovolaemia poorly (may develop flash pulmonary oedema with fluid overload)

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17. CLINICAL PEARLS

OT Pearls

1. "The patient's baseline is the target, not the textbook normal." In a patient whose usual BP is 160/100 mmHg, an intraoperative MAP of 65 mmHg IS hypotension for them - treat it.
2. The "first arm, then both arms" rule: Always measure BP in both arms at the preoperative visit. A significant difference (>15 mmHg SBP) should prompt investigation for subclavian stenosis or coarctation - both change your anaesthetic planning.
3. The single most effective manoeuvre to blunt the pressor response to laryngoscopy in clinical practice is adequate fentanyl dosing 3-5 minutes before laryngoscopy (2.5-5 mcg/kg). This is more reliable than lignocaine in most settings.
4. Desflurane at rapid increase in concentration triggers catecholamine release (central SNS stimulation) → acute hypertension and tachycardia. Never rapidly increase desflurane concentration in a hypertensive patient with IHD.
5. Check today's medications on the day of surgery. Many patients are confused about which drugs to take. The commonest error is patients taking their ACEi on the morning of surgery when they were told to hold it - and vice versa, not taking their beta-blocker.
6. Epidural anaesthesia for major abdominal and thoracic surgery in hypertensives: Reduces sympathetic response to surgical incision → better intraoperative BP control, reduced stress hyperglycaemia, reduced perioperative MI risk. But: Expect profound sympathectomy hypotension - ensure adequate preloading and vasopressor availability.
7. The "double load" of LVH: Hypertensive patients with LVH have diastolic dysfunction (stiff, non-compliant ventricle). They are exquisitely sensitive to: (a) hypovolaemia (preload-dependent; reduced filling → catastrophic fall in CO) and (b) tachycardia (reduced diastolic filling time → worse filling → worse CO). Aim for normovolaemia with controlled heart rate.

ICU Pearls

1. Postoperative hypertension in cardiac surgery ICU is most effectively treated with nicardipine infusion or clevidipine - both are rapid-acting, titratable CCBs that reduce afterload without causing coronary steal. GTN is the preferred first-line after coronary revascularisation (coronary dilator).
2. The PRES warning: Any patient with severe perioperative hypertension who develops seizures + visual changes in the ICU → think PRES (Posterior Reversible Encephalopathy Syndrome). MRI (not CT) shows T2/FLAIR white matter oedema in occipital/parietal regions. Treatment: controlled BP reduction → most cases fully reversible.
3. Methylene blue for vasoplegic syndrome: When BP is refractory despite vasopressin + norepinephrine (especially post-cardiopulmonary bypass or post-ACEi/ARB), methylene blue 1.5-2 mg/kg IV over 20 minutes inhibits guanylyl cyclase and reduces cyclic GMP → reverses NO-mediated vasodilation. Caution: can cause pulmonary vasoconstriction, serotonin syndrome (in SSRI patients), and interfere with pulse oximetry.

Pitfalls to Avoid

1. Never interpret a single clinic BP as the definitive value. White-coat hypertension affects 15-25% of patients - their surgical risk may be much lower than the clinic BP suggests. Conversely, masked hypertension (normal clinic BP but high home BP) may be missed. When in doubt, request ABPM or home BP log.
2. Beware hypovolaemia from chronic diuretic use. Many hypertensive patients are on thiazides or loop diuretics and present to surgery mildly volume-depleted. Add induction hypotension to ACEi/ARBs + volatile agents → severe vasoplegic state. Check electrolytes, correct hypokalaemia, give careful preloading.
3. The aortic dissection trigger: In the OT, severe uncontrolled hypertension + chest/back pain + pulse differential = aortic dissection until proven otherwise. Immediately: IV esmolol (heart rate control) + sodium nitroprusside (BP reduction to SBP <120 mmHg). Do NOT give pure vasodilators without beta-blockade first - reflex tachycardia increases aortic wall shear stress.

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18. KEY TAKE-HOME MESSAGES

1. Hypertension is the most prevalent preoperative comorbidity - 20-25% of surgical patients. Most present with essential hypertension; 5-10% have secondary causes requiring identification.
2. BP <180 mmHg systolic AND <110 mmHg diastolic does NOT independently increase perioperative risk - do not reflexively cancel surgery at these values. The 2026 AAGBI/BIHS guideline allows proceeding up to clinic BP of 180/120 mmHg if no prior documentation.
3. The presence of end-organ damage (LVH strain, retinopathy Grade III/IV, CKD, prior MI/stroke) is more important than the BP number alone in surgical risk stratification.
4. The autoregulation curve is shifted RIGHT in chronic hypertension. The LLA may be at MAP 70-80 mmHg. Target THEIR baseline, not "normal." Maintain within 20% of preoperative MAP.
5. The biphasic haemodynamic response (hypotension at induction → hypertension at laryngoscopy) is predictable in hypertensives. Anticipate it, prevent it, and treat it.
6. Hold ACEi/ARBs 24 hours before surgery to prevent refractory intraoperative hypotension. But restart as soon as haemodynamically stable postoperatively - omission causes rebound and adverse outcomes.
7. Never abruptly stop beta-blockers or clonidine perioperatively - rebound effects are dangerous and potentially fatal.
8. Vasopressin is the vasopressor of choice for ACEi/ARB-associated refractory hypotension - it bypasses the blocked RAAS entirely.
9. Attenuate the pressor response to laryngoscopy proactively in all hypertensives - use fentanyl + esmolol/labetalol + adequate depth. Pressor response peaks at 30-60 seconds; IHD + hypertension + uncontrolled response = ischaemia or arrhythmia.
10. The 2025 meta-analysis (PMID 41017370, 14 RCTs) confirms withholding ACEi/ARBs reduces intraoperative hypotension incidence (36.4% vs 48.4%), but evidence certainty is very low - individualise management.
11. Hypertensive emergency requires MAP reduction of no more than 25% in the first hour. Target 160/100 mmHg in hours 2-6. Faster reduction risks cerebral ischaemia below the shifted LLA.
12. Sodium nitroprusside: Most potent acute vasodilator; risks include cyanide toxicity, thiocyanate toxicity (renal failure), and increased ICP (avoid in neurosurgical cases). Protect from light.
13. LVH with S4 sound indicates diastolic dysfunction. These patients are preload-dependent and tachycardia-intolerant. Volume management is critical - neither dry nor overloaded.
14. In phaeochromocytoma: ALPHA BEFORE BETA - always. Give phenoxybenzamine for 7-14 days before adding beta-blocker. Phenylamine (phentolamine) IV for intraoperative crisis.
15. The POISE trial demonstrated that acute high-dose metoprolol started the night before surgery increased stroke and all-cause mortality despite reducing MI. Start beta-blockers only for established indications, not acutely before surgery.
16. Postoperative hypertension is common and dangerous - increases suture line disruption, bleeding, MI, and stroke risk. The commonest correctable cause is pain - treat it first.
17. Labetalol (combined alpha-1 + beta blockade) is the most versatile IV antihypertensive agent for acute perioperative use - controls both rate and pressure, does not cause reflex tachycardia.
18. White-coat hypertension (15-25% of referred patients) can lead to unnecessary postponement of surgery. ABPM or home BP monitoring reduces false-positive diagnoses and surgical delays.
19. Clonidine withdrawal produces one of the most severe rebound hypertensive states. Always ensure continuation perioperatively - if NPO, use transdermal or IV route.
20. The final lesson: Hypertension management in the perioperative period is fundamentally about understanding each patient's individual haemodynamic set point and maintaining it - not about achieving textbook "normal" values. A MAP of 70 mmHg can be hypotensive for one patient and hypertensive for another.

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References (Primary Sources Used)

• Miller's Anesthesia 10e (Gropper et al.), Chapter 38 (Preoperative Evaluation), pp. 3867-3868; Chapter 13 (Cerebrovascular Disease), pp. 1077-1078; Chapter 50 (Cardiac Surgery ICU), pp. 7499-7500
• Barash's Clinical Anesthesia 9e (Barash et al.), Chapter 23 (Preoperative Assessment), pp. 1761-1762
• Morgan & Mikhail's Clinical Anesthesiology 7e, Chapter 21 (Cardiovascular Physiology and Anesthesia), pp. 713-730 - Full hypertension section including pathophysiology, induction strategies, attenuation doses, and drug comparisons
• Harrison's Principles of Internal Medicine 22e (2025), Chapter 288 (Hypertension) - Definition, classification, secondary causes, lifestyle interventions, treatment targets; Chapter 495 (Geriatric Hypertension)
• 2026 AAGBI/BIHS Guideline (McCormack T et al., Anaesthesia 2026, PMID: 41532177) - Updated perioperative BP thresholds, measurement recommendations, surgical postponement criteria
• 2025 ACEi/ARB Meta-Analysis (Dou W et al., Ann Med 2025, PMID: 41017370) - 14 RCTs, 4063 patients; withholding reduces intraoperative hypotension but very low evidence certainty---

Session Summary

1. Move to a new topic - just type the topic name (e.g., Ischaemic Heart Disease, Thyroid Disease, Renal Failure, Obesity, Obstructive Sleep Apnoea, etc.)
2. Deeper dive into a specific subtopic within Hypertension - for example:
   • Hypertensive emergencies in detail
   • Phaeochromocytoma anaesthetic management
   • Pharmacology of specific antihypertensives
   • Neuraxial anaesthesia in hypertension
   • Postoperative hypertension
3. A clinical case scenario based on hypertension - e.g., uncontrolled hypertensive patient for emergency laparotomy
4. A focused viva drill on hypertension - rapid-fire questions and model answers

PLEURAL EFFUSION

Comprehensive MD Anaesthesiology Teaching Session

Sources: Miller's Anesthesia 10e | Barash's Clinical Anesthesia 9e | Morgan & Mikhail's Clinical Anesthesiology 7e | Harrison's Principles of Internal Medicine 22e | BTS/SEPAR 2022 Guidelines | ACR 2024 Appropriateness Criteria

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1. DEFINITION

Standard Textbook Definition

• The pleural space contains approximately 5-15 mL of fluid (some sources: 0.1-0.2 mL/kg body weight)
• Fluid enters from parietal pleural capillaries (high hydrostatic pressure, systemic circulation)
• Fluid is removed via parietal pleural lymphatics, which have the capacity to absorb 20 times the normal rate of fluid formation
• A net pressure gradient of approximately 0.3 cmH2O drives physiological fluid from parietal to visceral pleura and into lymphatics

Clinical Importance

• ~1.5 million new cases per year in the United States alone (Harrison's 22e)
• The third most common respiratory disorder encountered in clinical practice
• Perioperative significance: Pleural effusion impairs respiratory mechanics, reduces functional residual capacity (FRC), causes atelectasis, V/Q mismatch, and hypoxia - all of which are compounded under general anaesthesia
• Anaesthetic significance: Pre-existing pleural effusion increases risk of perioperative respiratory failure; the patient presenting for thoracentesis or chest drain under sedation presents specific procedural challenges; large effusions mandate modified ventilatory management

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2. INTRODUCTION

Background

Epidemiology

Relevance in Anaesthesia and Critical Care

1. Preoperative: Undiagnosed effusion may contribute to dyspnoea wrongly attributed to other causes; large effusion mandates drainage before elective surgery
2. Intraoperative: Under GA + PPV, pleural effusions worsen atelectasis, increase shunt fraction, reduce compliance, and impair oxygenation
3. Thoracic anaesthesia: Effusions complicate one-lung ventilation; ipsilateral effusion may fill operative field if drained intraoperatively
4. ICU: Post-cardiac surgery effusions, hepatic hydrothorax (liver ICU), ventilator-associated pleural effusions, post-thoracentesis complications
5. Procedures under anaesthesia/sedation: Thoracentesis, chest drain insertion, VATS (Video-Assisted Thoracoscopic Surgery) for empyema or malignant effusion

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3. BASIC SCIENCES

A. Anatomy of the Pleural Space

Layers

• Parietal pleura: Lines the chest wall, diaphragm, and mediastinum; innervated by phrenic (central diaphragm) and intercostal nerves (peripheral); pain-sensitive
• Visceral pleura: Covers the lung surface; innervated by autonomic fibres; NOT pain-sensitive (hence pleural pain = parietal irritation)
• Pleural space: Virtual space between the two layers; normally contains 5-15 mL thin serous fluid; maintains negative intrapleural pressure (-3 to -5 cmH2O at rest)

Vascular Supply

• Parietal pleura: Supplied by systemic circulation (intercostal arteries, internal mammary arteries) at mean pressure ~30 mmHg
• Visceral pleura: Supplied by bronchial arteries (systemic) and pulmonary arteries (pulmonary); lower pressure than parietal side
• Fluid moves from high pressure (parietal side) → low pressure (visceral side) → lymphatics

Lymphatic Drainage

• Primarily via parietal pleural lymphatics (stomata on mesothelial surface)
• Drains to internal mammary, intercostal, and mediastinal lymph nodes
• Capacity: up to 0.5 L/hour (20× normal production rate)
• Critical anaesthetic point: When lymphatic drainage is blocked (malignancy, post-irradiation), effusion accumulates regardless of hydrostatic/oncotic status

Intercostal Neurovascular Bundle

• Arrangement: Vein (V) - Artery (A) - Nerve (N) from top to bottom = VAN
• Located in the subcostal groove of the superior rib
• Needle/drain insertion: ALWAYS at the superior margin (upper edge) of the lower rib to avoid the neurovascular bundle
• Risk of injury: haemothorax, intercostal nerve damage

B. Physiology of Pleural Fluid Formation

Starling Forces in the Pleural Space

• Pc = capillary hydrostatic pressure (parietal: ~30 mmHg; visceral: ~11 mmHg)
• Pi = pleural space hydrostatic pressure (~-5 cmH2O = very slightly subatmospheric)
• πc = plasma oncotic pressure (~25-28 mmHg)
• πi = pleural fluid oncotic pressure (~5-8 mmHg)

Mechanisms of Effusion Formation

C. Pathophysiology of Respiratory Compromise

Effects on Lung Mechanics

• Accumulating fluid compresses the adjacent lung → collapse of alveoli
• Every 500 mL of pleural fluid decreases FVC by approximately 100-200 mL
• Compressive atelectasis primarily affects the lower lobes (dependent lung zones)

• Pleural fluid pushes the diaphragm down and compresses basal lung units
• Reduced FRC → closure of small airways during normal breathing → air trapping and shunting
• Critical under GA: Already reduced FRC by 15-20% with induction → further reduction by effusion → hypoxia

• Atelectatic regions receive perfusion (gravity-dependent blood flow) but no ventilation
• Creates intrapulmonary shunt (blood that passes through unventilated lung)
• Results in hypoxaemia refractory to supplemental O2 (shunt physiology)

• Very large effusion (>1.5 L) shifts the mediastinum to the contralateral side
• Compresses the contralateral lung and great vessels
• Reduces cardiac output (venous return impaired)
• Tension hydrothorax: Rapid accumulation (haemothorax, iatrogenic) → emergency

• Fluid reduces the spring-like recoil balance of the chest wall
• Increases the work of breathing
• Contributes to respiratory muscle fatigue

• Fluid beneath the diaphragm flattens it → loss of dome shape → inefficient contraction
• Particularly relevant in unilateral effusions and in mechanically ventilated patients

Effects Under General Anaesthesia

• Loss of spontaneous breathing → loss of dependent zone ventilation (PPV preferentially ventilates non-dependent zones)
• Effusion further loads the dependent lung → worsened atelectasis
• Increased Shunt Fraction → increasingly refractory hypoxaemia
• PEEP (Positive End-Expiratory Pressure) partially counteracts by recruiting alveoli BUT also redistributes fluid to less compressible areas

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4. CLASSIFICATION

A. By Mechanism: Transudates vs Exudates (Light's Criteria)

Light's Criteria (Richard Light, 1972) - Gold Standard

Key Exam Point: Light's criteria misclassify approximately 25% of transudates as exudates ("pseudoexudates"). This typically occurs in CHF patients treated with diuretics. When in doubt, also measure the serum-pleural fluid albumin gradient: if >1.2 g/dL → transudate (despite meeting Light's exudate criteria).

Additional Tests to Distinguish Transudates from Exudates

B. By Cause

Transudative Effusions (Systemic Factors Disturb Starling Forces)

Exudative Effusions (Local Factors Disturb Fluid Dynamics)

C. By Volume/Severity

D. By Parapneumonic Classification (Light's Parapneumonic Classification)

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5. ETIOLOGY AND RISK FACTORS

Common Causes by Frequency

Specific Perioperative Causes (High Anaesthetic Relevance)

Risk Factors for Complicated Parapneumonic/Empyema

• pH <7.2 in pleural fluid
• Pleural fluid glucose <60 mg/dL
• Positive Gram stain or culture
• Loculated effusion on imaging
• Pneumonia not responding to antibiotics
• Purulent fluid at aspiration
• Diabetics (2-4x risk of empyema)
• Immunosuppression

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6. CLINICAL FEATURES

Symptoms

Signs

Inspection

• Reduced expansion of the affected hemithorax
• Mediastinal/tracheal deviation to the contralateral side (large effusion)
• Engorged neck veins (SVC obstruction, cardiac tamponade)

Palpation

• Reduced or absent vocal fremitus over the effusion
• Stony dull percussion note - the most reliable sign
• Tracheal deviation (large effusion → contralateral)

Percussion

• Stony dullness (flat percussion note) over fluid - dull like a stone; contrasts with woody dullness of consolidation
• Shifting dullness in massive free-flowing effusion (fluid moves with position)

Auscultation

• Absent/reduced breath sounds over the effusion
• Bronchial breathing at the upper limit of the effusion (compressed, patent bronchus above the fluid - creates a resonant column for sound transmission)
• Aegophony (E-to-A change): At the upper margin, "E" is heard as "A" (nasal quality)
• Pleural friction rub: Early pleuritis before fluid accumulates; may disappear as fluid separates the pleural surfaces

Examination Findings by Position

Exam Mnemonic for Signs of Pleural Effusion - "SPACE": Sound (breath) - reduced/absent; Percussion - stony dull; Aegophony - at upper border; Chest movement - reduced ipsilaterally; Extension/Expansion - decreased

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7. DIAGNOSIS

Imaging

1. Chest X-Ray (CXR)

• Bilateral effusions with enlarged cardiac shadow: CHF
• Left-sided > right-sided: Pancreatitis, rupture of distal oesophagus
• Right-sided >> left-sided: Hepatic hydrothorax, sub-phrenic abscess
• Unilateral massive (no mediastinal shift): Mesothelioma, malignant effusion fixing mediastinum, tumour causing lung collapse

2. Ultrasonography (US) - Gold Standard for Guidance

• Detects as little as 5-50 mL of pleural fluid
• Differentiates free-flowing vs loculated effusion
• Distinguishes fluid from consolidation or tumour (common pitfall on CXR)
• Guides safe thoracentesis (reduces pneumothorax risk by 3-fold)
• Identifies optimal site for needle insertion
• Can estimate volume: Basal excess fluid height (cm) × 70 = approximate volume in mL

• Free fluid: Anechoic (black) space between visceral and parietal pleura
• Exudate/haemothorax: May have echogenic material, fibrin strands, septations
• Empyema: Complex, loculated, may have "plankton sign" (mobile echogenic particles)

3. Computed Tomography (CT Thorax)

• Loculated or complex effusions not well-characterised by US
• Identifying underlying cause (malignancy, pulmonary pathology, mediastinal disease)
• Contrast-enhanced CT: Distinguishes pleural empyema from lung abscess (split pleura sign - enhancing thickened pleural layers with fluid between)
• CT pulmonary angiography (CTPA): If PE suspected
• Planning surgical intervention (decortication)

4. Thoracic MRI

• Not routine
• Better for characterising pleural plaques, mesothelioma invasion, diaphragmatic involvement
• No radiation (useful in pregnant patients)

Thoracentesis (Diagnostic and Therapeutic)

Diagnostic Flowchart (Harrison's 22e - Figure 305-1)

Indications for Thoracentesis

• New unexplained pleural effusion (if >10 mm on lateral decubitus or US)
• Known cause but atypical features (fever in CHF, unilateral in CHF)
• Therapeutic drainage for symptomatic large effusion

Contraindications

• Absolute: None (in the presence of life-threatening effusion)
• Relative: Coagulopathy (INR >1.5-2.0), thrombocytopaenia (<50,000), small effusion (<10 mm), mechanical ventilation (relative - higher pneumothorax risk), contralateral pneumonectomy, inability to cooperate
• Do NOT routinely correct INR before thoracentesis if INR <3.0 (BTS recommendation)

Technique (Safe Thoracentesis)

1. Patient seated upright, arms forward on pillow
2. Ultrasound marking of optimal site (posterior, 1-2 intercostal spaces below fluid level)
3. Insert needle at upper border of lower rib (avoid VAN bundle)
4. Standard entry sites: 5th-9th intercostal space, posterior axillary line (or as guided by US)
5. Local anaesthesia: 1% lignocaine down to pleural surface; aspirate fluid at pleural surface to confirm position
6. Aspiration of fluid (15-20 mL for diagnostic; up to 1.5L for therapeutic)
7. Do NOT drain >1.5L at one sitting (risk of re-expansion pulmonary oedema)

Pleural Fluid Analysis - What to Send

Interpretation of Pleural Fluid

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8. MANAGEMENT

Medical Management

1. Transudative Effusions - Treat the Underlying Cause

• CHF: Diuretics (furosemide + spironolactone), ACEi/ARBs, beta-blockers, fluid restriction
• Cirrhosis/Hepatic Hydrothorax: Salt restriction, diuretics, TIPS (transjugular intrahepatic portosystemic shunt); repeated thoracentesis if refractory
• Nephrotic syndrome: Treat underlying nephropathy; ACEi; diuretics cautiously
• Hypothyroidism: Thyroid hormone replacement

2. Parapneumonic Effusion/Empyema

• pH <7.2 → Must drain
• Glucose <60 mg/dL → Must drain
• Positive Gram stain/culture → Must drain
• Visually purulent (frank empyema) → Must drain
• Loculated effusion → Drain with fibrinolytics or VATS

1. Small-bore chest drain (14-16 F): Preferred for non-purulent, free-flowing parapneumonic; less painful; equally effective as large-bore
2. Large-bore chest drain (28-36 F): Purulent empyema, haemothorax, trauma
3. Intrapleural fibrinolytics: tPA (alteplase) + DNase (Pulmozyme) → breaks down fibrin + DNA in loculated empyema; MIST-2 trial: tPA 10 mg BD + DNase 5 mg BD for 3 days → significantly reduced need for surgery
4. VATS (Video-Assisted Thoracoscopic Surgery): For organised/fibrinous empyema or failed medical treatment; breaks down loculations, decortication
5. Open decortication (thoracotomy): Stage IV (organised, chronic empyema with fibrous peel trapping lung)

3. Malignant Pleural Effusion (MPE)

1. Repeated therapeutic thoracentesis: For poor performance status patients; not definitive
2. Pleurodesis: Obliteration of pleural space to prevent recurrence
   • Chemical pleurodesis: Talc (most effective, 90% success), bleomycin, doxycycline
   • Technique: Drain effusion to <100 mL → instil talc slurry 4-5 g → rotate patient → remove drain 24-48h
   • Requires >400 mL/day drainage to confirm lung expansion before pleurodesis
   • Fails if trapped lung (lung cannot expand to appose chest wall)
3. Indwelling Pleural Catheter (IPC/Pleurx): Preferred for trapped lung or if patient wants outpatient management; drain 3x/week at home; spontaneous pleurodesis in 50%
4. VATS + talc pleurodesis: Surgical approach for good performance status

4. Haemothorax

• Small (<300 mL): Observe; may reabsorb
• Moderate-large (>300 mL): Large-bore chest drain (≥28 F)
• Massive haemothorax (>1500 mL or >200 mL/hr ongoing): Thoracotomy
• Fibrothorax (organized haemothorax): VATS or decortication within 4-6 weeks
• Traumatic: See ATLS protocol; surgical control if ongoing haemorrhage

5. Chylothorax

• Conservative: Low-fat diet + medium-chain triglycerides (MCT); bowel rest + TPN; octreotide (reduces thoracic duct flow)
• Surgical: Thoracic duct ligation (VATS); pleurodesis if inoperable
• Etilefrine (sympathomimetic) can close the duct opening in post-surgical chylothorax

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9. ANAESTHETIC CONSIDERATIONS

A. Preoperative Assessment

History

1. Duration and cause of effusion
2. Volume and rate of accumulation
3. Prior thoracentesis and response
4. Degree of dyspnoea: At rest? On exertion? Orthopnoea?
5. Associated conditions: Malignancy, cardiac failure, cirrhosis, TB
6. Medications: Anticoagulants (relevant for procedures), diuretics, antivirals

Examination

• Respiratory rate, SpO2 on air
• Signs of effusion (described above)
• Signs of tracheal deviation (large effusion - assess severity)
• Hepatic/cardiac signs (underlying cause)
• Bilateral leg oedema (DVT, cardiac cause)
• Signs of malignancy, lymphadenopathy

Investigations

• CXR/CT thorax - assess volume, loculation, mediastinal position
• ABG - assess gas exchange impairment (PaO2, PaCO2, shunt fraction)
• PFTs (Spirometry) - assess degree of restrictive defect (if indicated before major surgery)
• Echocardiography - if cardiac cause suspected; assess LV/RV function
• Serum albumin, LFTs - if hypoalbuminaemia suspected
• Coagulation - if procedure planned

Preoperative Optimisation

• Should large effusion be drained before elective surgery?
  • Yes, if moderate-large effusion (>500 mL) and elective thoracic or major abdominal surgery
  • Yes, if SpO2 <94% on air attributable to effusion
  • Drain first if respiratory compromise is the dominant preoperative risk
  • For minor surgery with small asymptomatic effusion: Proceed without drainage; use high FiO2; PEEP strategies

B. Anaesthetic Management for Thoracentesis or Chest Drain Insertion

Positioning

• Thoracentesis/Small-bore drain: Patient seated upright, arms resting forward (widens intercostal spaces posteriorly)
• If unable to sit (sedated/ICU patient): Lateral decubitus with affected side up; or supine with ultrasound guidance

Sedation/Anaesthesia for Procedure

• Most thoracenteses: Local anaesthesia (1-2% lignocaine) ± minimal sedation (midazolam 1-2 mg IV)
• Anxious/uncooperative patients: IV midazolam + fentanyl; use caution if already hypoxic
• For VATS or pleurodesis under GA: See thoracic anaesthesia considerations below

Local Anaesthesia Technique for Thoracentesis

1. Identify the intercostal space 1-2 spaces below the upper border of the effusion
2. Infiltrate skin and subcutaneous tissue with 1% lignocaine
3. Advance needle over the upper border of the lower rib (to avoid neurovascular bundle)
4. Infiltrate periosteum of rib, parietal pleura (most painful step) generously
5. Aspirate fluid to confirm position
6. Proceed with drainage needle/cannula
7. Key: Adequate pleural anaesthesia is essential - the parietal pleura is richly innervated by intercostal nerves

Exam Point: The parietal pleura is innervated by intercostal nerves (lateral and posterior portions) and the phrenic nerve (central diaphragmatic portion). Visceral pleura is NOT pain-sensitive. Hence thoracentesis is painful at the parietal level only.

C. Anaesthetic Management for Surgery on a Patient with Pleural Effusion

Pre-induction Considerations

• Large effusion: Drain before induction if possible (even partial drainage - 1L - improves FRC and oxygenation significantly)
• Position on induction: If effusion is unilateral and patient cannot tolerate supine, consider induction in semi-recumbent or lateral position
• Pre-oxygenation: Critical; already reduced FRC → rapid oxygen desaturation; pre-oxygenate for minimum 3-5 minutes with 100% O2; consider high-flow nasal O2 (HFNO) during induction
• IV access: Ensure adequate, functional IV access before induction

Induction

• Avoid: Sudden position changes that redistribute effusion volume and further compress remaining functional lung
• Propofol: Preferred induction agent; may require lower dose if cardiovascular compromise from large effusion
• Airway: Standard tracheal intubation; in respiratory compromised patients, consider awake fibreoptic intubation if difficult airway anticipated
• RSI: If suspected full stomach (large effusion causing gastric compression/aspiration risk)

Intraoperative Ventilation Strategies

• FiO2: Start at 0.5-1.0 (high shunt fraction); titrate to SpO2
• PEEP: Apply PEEP 5-10 cmH2O to recruit atelectatic lung around the effusion
• Tidal volume: 6-8 mL/kg IBW (lung-protective); avoid high plateau pressures
• Positioning: Lateral decubitus with affected side DOWN compresses the effusion against the chest wall and may paradoxically improve perfusion-ventilation matching in the upper (healthy) lung
• Pressure-controlled ventilation: May be preferred if compliance is very low (lower peak pressures for same tidal volume)

• Effusion on the operative side: Drain early in the procedure to allow lung expansion for anaesthetic field of view
• Risk of contamination: If purulent empyema, isolate the lung with double-lumen tube BEFORE drainage to prevent spillage of infected material into healthy lung
• Priority in empyema surgery: DOUBLE-LUMEN TUBE + ISOLATE FIRST

Critical Anaesthetic Pearl: In empyema with pus in the pleural space, use a double-lumen endotracheal tube (DLT) and establish one-lung ventilation with the healthy lung ventilated BEFORE opening the thorax. This prevents spillage of infected pleural fluid into the contralateral lung, which can cause devastating bilateral pneumonia/ARDS.

Monitoring

• SpO2: Continuous; be prepared for periods of severe desaturation during OLV
• Capnography: EtCO2 may underestimate PaCO2 in severe V/Q mismatch (large dead space)
• ABG: Frequent intraoperative; essential in OLV
• Arterial line: For major thoracic surgery, large effusion, haemodynamically unstable patients
• Bronchoscopy: Verify DLT position after patient positioning

Fluid Management

• Avoid excessive IV fluids in patients with low oncotic pressure (hypoalbuminaemia, malignancy) - promotes re-accumulation
• Use goal-directed fluid therapy
• Colloid (albumin) may be preferable in hypoalbuminaemic patients

D. Specific Scenarios

1. Re-expansion Pulmonary Oedema (RPO)

• Definition: Non-cardiogenic pulmonary oedema occurring after rapid re-expansion of a collapsed lung following drainage of large pleural effusion or pneumothorax
• Incidence: 0.2-1% of thoracenteses; higher with large volumes or long-standing effusion
• Pathophysiology: Rapid lung re-expansion → surfactant injury → increased capillary permeability → flooded alveoli
• Risk factors: Large effusion (>1.5 L), rapid drainage, long-standing (>3 days) effusion, young males, bilateral effusion
• Prevention: Do NOT drain >1.5 L at one session; if large effusion, drain 1-1.5L, then stop; allow 24-48h before further drainage; monitor symptoms during drainage
• Features: Cough, chest tightness, hypoxia developing during or immediately after drainage; CXR: unilateral alveolar opacities ipsilateral to drained side
• Treatment: Supplemental O2; CPAP/NIV; rarely requires intubation; self-limiting in most cases

HIGH-YIELD EXAM POINT: The maximum safe volume to drain in a single session is 1.5 litres. Beyond this, the risk of re-expansion pulmonary oedema increases significantly. Always stop drainage if the patient develops chest pain, cough, or oxygen desaturation.

2. Thoracentesis Complications

3. Hepatic Hydrothorax in Liver Failure Patients

• Right-sided transudative effusion in cirrhosis due to passage of ascitic fluid via diaphragmatic defects
• Anaesthetic challenge: Concurrent hypoalbuminaemia, coagulopathy (INR elevated), thrombocytopaenia, encephalopathy risk, hepatorenal syndrome
• Management: Treat ascites (diuretics, salt restriction, TIPS); repeated thoracentesis for symptom relief; pleurodesis difficult (lung often cannot expand fully); liver transplantation is definitive
• Thoracentesis in decompensated cirrhosis: Higher bleeding risk (coagulopathy); higher infection risk; encephalopathy can be precipitated

4. Pleural Effusion in Mechanically Ventilated ICU Patients

• Prevalence: ~62% of ICU patients develop pleural effusion
• Causes: Fluid overload, hypoalbuminaemia, cardiac dysfunction, pneumonia, ARDS
• Effect on ventilation: Increases atelectasis, impairs compliance, worsens oxygenation, may increase ventilator days
• Should all ICU effusions be drained? No evidence for routine drainage in asymptomatic small effusions; drain if:
  • Diagnostic uncertainty (exclude empyema)
  • Large effusion with significant respiratory compromise
  • V/Q mismatch contributing to ventilator weaning failure
• Technique in ventilated patients: US-guided; lateral decubitus or semi-prone; keep PEEP constant during procedure; small-bore drain preferred; monitor for pneumothorax and cardiac effects (large drainage can cause mediastinal shift)

5. Post-Cardiac Surgery Effusion

• Small serous left-sided effusion: Day 1-7; benign; monitor
• Blood-stained (haemothorax): Chest drain immediately; monitor output (>200 mL/hr x 2h → return to theatre)
• Dressler's Syndrome (Post-Cardiac Injury Syndrome): Weeks 2-12 post-surgery; pericarditis + bilateral pleuritis + fever; treat with aspirin/NSAIDs ± colchicine; avoid anticoagulation

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10. DRUGS

A. Local Anaesthetics for Thoracentesis/Chest Drain

B. Intrapleural Fibrinolytics (for Empyema)

tPA (Alteplase) + DNase (MIST-2 Protocol)

C. Chemical Pleurodesis Agents

D. Octreotide (for Chylothorax)

E. Diuretics (for Transudative Effusion)

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11. SCORES, FORMULAE, AND NUMERICAL VALUES

Key Numerical Values

Important Formulae

1. Mean Arterial Pressure (relevant for haemothorax/shock management)

2. Estimated Pleural Effusion Volume (Ultrasound Method)

• More accurate formula: Volume (mL) = 16 × (measured height of fluid in mm on supine CXR) - 38

3. Alveolar-Arterial (A-a) Oxygen Gradient

• Normal A-a gradient: Age/4 + 4 mmHg (increases with age)
• In pleural effusion: A-a gradient elevated (shunt + V/Q mismatch)
• Does NOT correct with supplemental O2 in significant shunt (distinguishes shunt from simple V/Q mismatch)

4. Intrapulmonary Shunt Fraction (Qs/Qt)

• CcO2 = End-capillary O2 content (assuming full O2 saturation)
• CaO2 = Arterial O2 content
• CvO2 = Mixed venous O2 content
• Normal Qs/Qt: 2-5%
• With large pleural effusion: Qs/Qt may be 15-25%

5. Light's Criteria - Worked Example

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12. GUIDELINES

1. British Thoracic Society (BTS) Guidelines on Pleural Disease

• Pleural Effusion 2010 (most cited); updated with specific sections 2014-2022
• Key recommendations: Ultrasound-guided thoracentesis; small-bore drains preferred; measure pH for parapneumonic; pleurodesis decision based on fluid drainage <150 mL/day

2. SEPAR/Spanish Society Guidelines 2022 (PMID: 36273933)

• Comprehensive update covering epidemiology, diagnosis, prognosis, and therapeutics
• Recommends multidisciplinary approach for malignant pleural effusion (MPE)
• IPCC (Indwelling Pleural Catheter) equally effective to talc pleurodesis for MPE

3. ACR Appropriateness Criteria 2024 (PMID: 38823955)

• Ultrasound is the most appropriate initial imaging for pleural disease and procedure guidance
• CT thorax with contrast for complex/unexplained effusion or when malignancy suspected
• CTPA when PE-associated effusion suspected

4. MIST-2 Trial (Rahman et al., NEJM 2011) - Practice Changing

• RCT of intrapleural tPA + DNase vs each alone vs placebo for pleural infection
• Combination tPA+DNase significantly reduced need for surgical intervention and hospital stay
• Now standard of care for loculated parapneumonic/empyema not responding to drainage alone

5. Pediatric Empyema - 2023 Living Network Meta-Analysis (PMID: 37463660)

• Surgery (VATS) superior to intrapleural fibrinolytics for paediatric empyema
• Different from adult recommendation where fibrinolytics are tried first

6. Surgery vs Fibrinolytics for Complicated Pleural Infections (Chang et al., 2024 - PMID: 39182102)

• Meta-analysis: 8 studies, 698 patients
• No significant difference in clinical failure, length of stay, or mortality between VATS and intrapleural fibrinolytics in adults
• Supports current practice of fibrinolytics first (less invasive) with VATS reserved for failure

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13. IMPORTANT TABLES

Table 1: Transudate vs Exudate - Comprehensive Comparison

Table 2: Causes of Pleural Effusion by Appearance

Table 3: Perioperative Considerations for Specific Effusion Types

Table 4: Chest Drain Sizes and Indications

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14. FLOWCHARTS AND ALGORITHMS

Algorithm 1: Diagnostic Approach to Pleural Effusion (Harrison's 22e)

NEW PLEURAL EFFUSION IDENTIFIED
              ↓
  CHEST IMAGING (US / CXR / CT)
  Confirm effusion; estimate volume;
  assess for loculation; guide aspiration
              ↓
   Is effusion >10 mm on lateral decubitus
   or >1 cm on ultrasound?
        /              \
      YES               NO
       ↓                 ↓
  DIAGNOSTIC             Monitor; treat
  THORACENTESIS          suspected cause
  Measure PF protein,
  LDH (and serum values)
              ↓
  APPLY LIGHT'S CRITERIA
  (PF/serum protein >0.5 OR
   PF/serum LDH >0.6 OR
   PF LDH >2/3 UNL)
        /              \
      YES               NO
       ↓                 ↓
    EXUDATE           TRANSUDATE
       ↓               ↓
  Further workup:    Treat CHF,
  Cytology,          cirrhosis,
  Glucose, pH,       nephrosis
  Culture/Gram stain ↓
  ADA (TB),          If persists:
  Triglycerides      Reconsider; add
  Amylase           albumin gradient
       ↓
  Glucose <60 mg/dL?
  Consider: Malignancy /
  Bacterial infection /
  Rheumatoid pleuritis
       ↓
  No diagnosis after above?
       ↓
  Consider PE → CTPA
  Consider TB → ADA/PCR/biopsy
  Symptoms improving? → Observe
  Not improving → Thoracoscopy/biopsy

Algorithm 2: Management of Parapneumonic Effusion/Empyema

PARAPNEUMONIC EFFUSION IDENTIFIED
              ↓
         THORACENTESIS
    Measure: pH, glucose, LDH,
    Gram stain, culture
              ↓
  Does ANY of the following apply?
  • pH <7.2
  • Glucose <60 mg/dL
  • Positive Gram stain or culture
  • Frank pus aspirated
  • Loculated effusion on US/CT
        /              \
       NO               YES
        ↓                ↓
  ANTIBIOTICS ALONE   DRAIN THE PLEURAL SPACE
  Re-assess in 24-48h
                       ↓
             IS FLUID DRAINING FREELY?
              /                    \
            YES                     NO
             ↓                       ↓
  Continue drain + ABX          INTRAPLEURAL
  Monitor for improvement         FIBRINOLYTICS
                                  tPA 10 mg + DNase 5 mg
                                  BD × 3 days
                                       ↓
                                 Fluid draining now?
                                  /           \
                                YES            NO
                                 ↓              ↓
                              Continue      VATS ±
                              drain + ABX   Decortication
                                       ↓
                           DEFINITIVE DRAINAGE ACHIEVED
                           Switch to oral ABX when
                           afebrile + improving + drain <50 mL/day

Algorithm 3: Anaesthetic Management of Patient with Pleural Effusion Undergoing Surgery

PATIENT WITH PLEURAL EFFUSION FOR SURGERY
               ↓
ASSESS SEVERITY (Volume, bilateral, SpO2, ABG)
               ↓
    SpO2 <94% or Large effusion (>500 mL)
    AND Elective surgery?
         /                  \
       YES                    NO
        ↓                      ↓
  DRAIN BEFORE SURGERY      Proceed with precautions:
  (Thoracentesis ≤1.5L)     • High FiO2
  Re-assess and              • PEEP 5-10 cmH2O
  re-schedule surgery        • Lung-protective ventilation
                             • A-line ± CVP
               ↓
   INTRAOPERATIVE MANAGEMENT
        ↓
  Pre-oxygenation: 3-5 min 100% O2
  Induction: Titrate carefully (may need lower doses)
  Intubation: Consider DLT if VATS for empyema
        ↓
  VENTILATION STRATEGY:
  • FiO2 0.5-1.0 (titrate SpO2)
  • TV: 6-8 mL/kg IBW
  • PEEP: 5-10 cmH2O
  • Rate: 12-16/min
  • Monitor: SpO2, EtCO2, peak/plateau pressure
        ↓
  POSITIONING:
  Unilateral effusion → consider affected side DOWN
  (may improve V/Q in healthy upward lung)
        ↓
  EMPYEMA → DLT → ISOLATE HEALTHY LUNG FIRST
  before opening thorax
        ↓
  POSTOPERATIVE: HDU/ICU if large effusion;
  continuous SpO2 monitoring; pain control (regional
  if possible); drain management; early physiotherapy

Algorithm 4: Re-expansion Pulmonary Oedema Prevention During Thoracentesis

THERAPEUTIC THORACENTESIS FOR LARGE EFFUSION
               ↓
  Commence drainage (US-guided)
               ↓
  DRAIN UP TO 1000-1500 mL MAXIMUM
               ↓
  Monitor CONTINUOUSLY during drainage:
  • SpO2 every 5 minutes
  • Patient symptoms (chest tightness, cough)
  • Drainage volume
               ↓
  Patient develops: cough, chest pain, SpO2 ↓?
        /                            \
      YES                             NO
       ↓                               ↓
  STOP DRAINAGE                  Continue to 1.5L
  O2 supplementation             maximum, then stop
  Consider CPAP/NIV
  CXR: RPO?                      Wait 24-48h for
  Treat as non-cardiogenic        lung to stabilise,
  pulmonary oedema                then drain further

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15. FREQUENTLY ASKED MD VIVA QUESTIONS

Short Viva Questions

Long Viva Questions

• Rapid assessment: SpO2 (likely low), RR (tachypnoeic), ability to lie flat (orthopnoea)
• ABG: PaO2, PaCO2 (type I or II respiratory failure?), pH
• CXR/portable US: Confirm bilateral massive, estimate volume, tracheal position
• Urgent bilateral thoracentesis (1-1.5L per side) BEFORE induction - even 30 minutes of drainage dramatically improves gas exchange and FRC
• If too unstable for drainage first: Proceed to surgery with full anticipation of difficult oxygenation
• Investigations: ECG, electrolytes, coagulation, group & screen
• Consider ICU/HDU booking for postoperative care

• Semi-recumbent or head-up position (reduces dependent lung compression)
• Pre-oxygenation: 5 min with 100% O2 (reduced FRC = smaller O2 reserve); HFNO during laryngoscopy if available
• RSI (full stomach risk - laparotomy indication often associated with abdominal pathology that caused effusions)
• Ketamine + suxamethonium (haemodynamically compromised) or propofol (titrated slowly) + suxamethonium
• Rapid intubation; immediately start PEEP

• FiO2 1.0 initially; titrate to SpO2
• Lung-protective ventilation: TV 6 mL/kg IBW; PEEP 8-12 cmH2O; Pplat <30 cmH2O; rate 14-18/min
• Invasive arterial monitoring (A-line): Continuous BP + ABG access
• Central venous access if major fluid shifts expected
• Consider intraoperative drainage of effusion if accessible (surgeon's help during abdominal surgery)
• Prone to desaturation: Have 100% FiO2, increased PEEP, and recruitment manoeuvres ready
• Balanced anaesthesia; minimal fluid overload

• Mandatory ICU/HDU admission
• Continue ventilation if PaO2/FiO2 <200 mmHg postoperatively
• Bilateral chest drain or repeated thoracentesis when coagulation permits
• Early physiotherapy, upright positioning, non-invasive ventilation if extubated

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16. MD THEORY EXAMINATION POINTS

Highly Probable University Questions

1. "Classify pleural effusion. Describe Light's criteria with diagnostic significance" - Most commonly repeated in theory exams
2. "Write notes on: management of malignant pleural effusion"
3. "Write notes on: re-expansion pulmonary oedema - pathophysiology, prevention, treatment"
4. "Discuss the anaesthetic management of a patient with large pleural effusion posted for VATS"
5. "Describe thoracentesis - indication, technique, complications"
6. "Compare transudate and exudate pleural effusions"
7. "Write notes on: empyema thoracis - classification and management"

High-Yield Facts

• Normal pleural fluid: 5-15 mL; lymphatics can absorb 20× normal formation rate
• Light's criteria: PF/serum protein >0.5; PF/serum LDH >0.6; PF LDH >2/3 UNL → any ONE = exudate
• 25% misclassification of transudates as exudates (diuresed CHF); correct with albumin gradient >1.2 g/dL
• Most common cause of transudative effusion: Left ventricular failure
• Most common cause globally in developing countries: TB
• Most common cause of exudate: Parapneumonic (bacterial pneumonia) in developed world
• Maximum drainage per session: 1.5 litres (re-expansion oedema prevention)
• pH <7.2 → drain the pleural space
• Double-lumen tube mandatory for VATS in empyema
• ADA >40 U/L → tuberculosis (90% sensitivity)
• PF glucose <30 mg/dL → rheumatoid pleuritis (pathognomonic)
• Anchovy sauce effusion → Amoebic abscess rupture
• Talc pleurodesis = most effective chemical agent (~90% success)
• tPA + DNase (MIST-2) = gold standard for loculated parapneumonic/empyema
• Hepatic hydrothorax → usually right-sided (~85%); ascites via diaphragmatic defects
• Meigs' syndrome = ovarian fibroma + right-sided pleural effusion + ascites

Memory Aids and Mnemonics

Light's Criteria: "PLP"

• Protein ratio PF/serum >0.5
• LDH ratio PF/serum >0.6
• PF LDH > 2/3 upper normal limit

Causes of Transudative Effusion: "CHAMPS"

• Congestive heart failure
• Hypothyroidism/Hypoalbuminaemia
• Ascites/cirrhosis (hepatic hydrothorax)
• Myxoedema
• Peritoneal dialysis
• SVC obstruction/Nephrotic Syndrome

Signs of Pleural Effusion: "SPACE"

• Sounds (breath) absent
• Percussion stony dull
• Aegophony at upper border
• Chest movement reduced ipsilaterally
• Expansion decreased

When to DRAIN Parapneumonic: "GPF"

• Glucose <60 mg/dL
• PH <7.2
• Frank pus

Causes of Exudative Effusion: "MALT CHOPS"

• Malignancy
• Asbestos (benign asbestos effusion)
• Lupus/connective tissue disease
• TB (and other infections)
• Chylothorax
• Haemothorax
• Oesophageal rupture (↑ amylase, ↓ pH)
• Pulmonary embolism
• Subphrenic/post-abdominal

Fluids and Their Diagnoses: "Colour Code"

• Clear pale yellow = Transudate
• Milky white = Chylothorax
• Bloody = Malignancy/Trauma/PE
• Anchovy sauce = Amoeba
• Black = Aspergillus
• Pus = Empyema

Common Mistakes Made by Residents

1. Draining >1.5 L in one session without monitoring for RPO
2. Not measuring pH in parapneumonic effusions (pH <7.2 = mandatory drainage)
3. Not using ultrasound guidance for thoracentesis → 3-7x higher pneumothorax rate without US
4. Inserting chest drain at the lower border of a rib → lacerating the neurovascular bundle
5. Misclassifying a diuresed CHF transudate as exudate using Light's criteria alone (forgetting the albumin gradient correction)
6. Failing to isolate the lung with DLT before opening a thoracic empyema → bilateral lung contamination
7. Confusing chylothorax with pseudochylothorax - both are milky; differentiate by TG (>110 mg/dL = chylothorax; cholesterol elevated = pseudochylothorax)
8. Misidentifying Meigs' syndrome - ovarian FIBROMA (not other ovarian tumours) + right-sided effusion + ascites; effusion resolves after tumour removal
9. Ignoring that PF glucose <30 mg/dL is pathognomonic of rheumatoid pleuritis (not just low - VERY low)
10. Not recognising oesophageal rupture as cause of left-sided effusion with very high amylase + very low pH + mediastinal emphysema → surgical emergency requiring immediate intervention

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17. CLINICAL PEARLS

OT Pearls

1. "The lung is your ally in pleural disease management." If you can drain the effusion and re-expand the lung before surgery, you transform the respiratory mechanics dramatically. Even draining 500-800 mL preoperatively (even if incomplete drainage) markedly improves FRC and oxygenation before induction.
2. The empyema patient for VATS is among the highest-risk thoracic anaesthesia scenarios. The combination of sepsis (haemodynamic instability), bilateral ventilation dependence, and need for lung isolation with a DLT requires meticulous preparation. Always verify DLT position with fibreoptic bronchoscopy, BEFORE the patient is repositioned to lateral decubitus.
3. Pre-oxygenation matters more than usual in patients with pleural effusion. Their reduced FRC means the oxygen reservoir in their lungs is already diminished. A full 5 minutes of pre-oxygenation (ideally with 15° head-up position) and use of high-flow nasal oxygen (HFNO) at 15L/min during laryngoscopy is standard in the modern era.
4. During thoracentesis under sedation: ALWAYS position the patient correctly first. The seated, forward-leaning position widens intercostal spaces, optimises the drainage angle, and allows gravity-dependent pooling for easier aspiration. Draining a patient supine via needle is technically challenging and risks injury.
5. The mediastinal shift in massive unilateral effusion creates a physiological paradox: The contralateral lung is compressed by mediastinal shift and may also have impaired ventilation. When you drain the massive effusion, the mediastinum returns to midline - but this sudden shift can cause haemodynamic instability (right heart geometry changes, sudden increased venous return). Drain slowly; have vasopressors ready.

ICU Pearls

1. In ICU patients with unexplained ventilator deterioration (rising FiO2 requirement, worsening compliance), always look for pleural effusion. Bilateral effusions develop in >60% of ventilated ICU patients and can be missed on supine AP CXRs. A quick bedside POCUS (Point-of-Care Ultrasound) of both lungs immediately identifies pleural fluid, differentiates it from consolidation, and guides drainage.
2. The "passive flooding" principle in ICU pleural effusions: In a ventilated patient with bilateral effusions secondary to fluid overload, draining the lungs (diuresis/ultrafiltration) is often more effective than thoracentesis. Aggressive diuresis in a fluid-overloaded patient can resolve bilateral transudative effusions without any procedural intervention.
3. Hepatic hydrothorax in liver failure ICU patients is one of the most challenging management scenarios. Thoracentesis provides temporary relief but effusion re-accumulates rapidly. TIPS reduces portal pressure and can control hepatic hydrothorax but carries risks of hepatic encephalopathy. Liver transplantation is the only definitive treatment.
4. Post-cardiac surgery haemothorax: Any chest drain output >200 mL/hr for 2 consecutive hours, or >1500 mL in the first 8 hours post-cardiac surgery, mandates surgical re-exploration. Do not wait. Coagulation replacement (FFP, platelets, cryoprecipitate) should be given concurrently but should NOT delay surgical decision-making.

Practical Tips

1. When in doubt about empyema vs lung abscess on CT: Look for the split pleura sign (enhanced thickening of both visceral and parietal pleura with fluid between). Empyema has this sign; lung abscess does NOT (it has a single wall within the lung parenchyma). This distinction changes management completely - empyema needs pleural drainage; lung abscess needs antibiotics ± percutaneous drainage.
2. Chylothorax after oesophagectomy or pneumonectomy: Suspect if chest drain output is milky, or if clear output increases dramatically after patient starts eating (oral fat triggers thoracic duct flow). Confirm with triglycerides >110 mg/dL. Start management: NPO + TPN + octreotide. Most resolve within 2-3 weeks conservatively; if >1500 mL/day persists → surgical ligation.

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18. KEY TAKE-HOME MESSAGES

1. Pleural effusion = abnormal excess fluid in the pleural space from imbalanced Starling forces, infection, malignancy, or blocked lymphatics. Normal volume: 5-15 mL; lymphatics can absorb 20× the normal production rate.
2. Light's criteria (1972) remain the gold standard for classifying transudates vs exudates. ANY ONE of three criteria met = exudate. However, they misclassify 25% of transudates as exudates; correct with serum-PF albumin gradient >1.2 g/dL → confirms transudate.
3. Most common cause of transudate worldwide = Left Ventricular Failure. Most common cause of exudate in developed countries = Parapneumonic. In developing countries = Tuberculosis.
4. Ultrasound is the gold standard for identifying, characterising, and guiding procedures on pleural effusions. Use it routinely. It reduces pneumothorax rate from thoracentesis by 3-fold.
5. Never drain more than 1.5 litres in a single session. Re-expansion pulmonary oedema is the feared complication. Stop immediately if the patient develops cough, chest tightness, or oxygen desaturation during drainage.
6. Parapneumonic effusion must be drained if pH <7.2, glucose <60 mg/dL, or frank pus is present. Antibiotics alone are insufficient in these circumstances. Use the "GPF" mnemonic: Glucose <60, pH <7.2, Frank pus.
7. For empyema/VATS under GA: DOUBLE-LUMEN TUBE IS MANDATORY. Isolate the healthy lung BEFORE opening the thorax to prevent contamination of the contralateral lung with infected material.
8. Pleural effusion reduces FRC, increases V/Q mismatch, creates intrapulmonary shunt, and worsens with GA + PPV. Pre-oxygenate aggressively; use PEEP; drain large effusions before elective major surgery.
9. MIST-2 protocol (tPA 10 mg + DNase 5 mg BD × 3 days) is now the standard for loculated parapneumonic/empyema not freely draining. Combination therapy significantly reduces need for surgery vs single agent.
10. PF glucose <30 mg/dL is pathognomonic of rheumatoid pleuritis. PF pH <7.0 with very high amylase = oesophageal rupture (surgical emergency). PF TG >110 mg/dL = chylothorax.
11. Hepatic hydrothorax is right-sided in 85% of cases. It arises from ascitic fluid moving via diaphragmatic defects. These patients carry triple anaesthetic risk: coagulopathy, encephalopathy, and porto-pulmonary hypertension.
12. Talc pleurodesis is the most effective chemical agent (~90% success) for malignant pleural effusion. Indwelling pleural catheters (IPC) are equivalent to talc pleurodesis and preferred when the lung is trapped.
13. The split pleura sign on contrast CT (enhancing thickened visceral + parietal pleura with fluid between) = empyema. Distinguishes empyema from lung abscess and guides management.
14. Re-expansion pulmonary oedema (RPO) is non-cardiogenic, ipsilateral, and caused by rapid lung expansion. Treat with O2, CPAP/NIV; it is usually self-limiting.
15. Adenosine Deaminase (ADA) >40 U/L in pleural fluid = TB effusion (90% sensitivity, 92% specificity). The most useful screening test for TB pleuritis in high-burden countries.
16. Intercostal drain insertion: Always at the upper border of the lower rib (superior margin) to avoid the VAN bundle (Vein-Artery-Nerve) in the subcostal groove. Never below the 9th ICS (risk of diaphragm/viscus injury).
17. For malignant pleural effusion: Treat the cause if possible (chemotherapy, radiotherapy); if non-responsive, offer IPC or talc pleurodesis based on performance status and lung expansion ability.
18. In the ICU: Pleural effusions develop in >60% of ventilated patients. Always consider in deteriorating gas exchange. Bedside POCUS should be part of the daily assessment of mechanically ventilated patients.
19. Chylothorax = milky fluid + TG >110 mg/dL. Always distinguish from pseudochylothorax (also milky but cholesterol-predominant, TG normal/low; seen in old TB or RA). Management: NPO + TPN + octreotide; surgery if >1500 mL/day.
20. The fundamental anaesthetic principle with pleural effusion: Understand the physiology - the fluid compresses lung → reduced FRC → shunt → hypoxia. Every management decision (whether to drain preoperatively, how to ventilate, whether to use DLT) flows logically from this single physiological principle.

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References

• Harrison's Principles of Internal Medicine 22e (2025), Chapter 305: Pleural Effusion - Definition, pathophysiology, Light's criteria, diagnostic flowchart (Figure 305-1), cause classification, full management
• Miller's Anesthesia 10e - Respiratory Acidosis and V/Q mismatch; pleural effusion as cause of ventilation-perfusion disturbance; thoracic anaesthesia one-lung ventilation considerations
• Morgan & Mikhail's Clinical Anesthesiology 7e - Thoracic anaesthesia; ventilatory strategies for respiratory compromise; one-lung ventilation
• Barash's Clinical Anesthesia 9e - Preoperative pulmonary evaluation; thoracic anaesthetic implications of pleural disease
• BTS Guidelines on Management of Pleural Disease (multiple updates 2010-2022)
• SEPAR Guidelines 2022 (PMID: 36273933) - Comprehensive Spanish Society guideline; diagnosis and treatment update
• ACR Appropriateness Criteria 2024 (PMID: 38823955) - Ultrasound as preferred modality
• MIST-2 Trial (Rahman et al., NEJM 2011) - tPA + DNase for pleural infection
• Surgery vs fibrinolytics meta-analysis (Chang et al., Respir Res 2024, PMID: 39182102)---

Session Summary