Diabetes Mellitus: Definition, Perioperative Regimens, and Intraoperative Glucose Control

1. DEFINITION OF DIABETES MELLITUS (3 marks)

• Fasting plasma glucose >= 126 mg/dL (7.0 mmol/L), or
• 2-hour plasma glucose >= 200 mg/dL during OGTT, or
• Random plasma glucose >= 200 mg/dL with symptoms, or
• HbA1c >= 6.5%

2. PREOPERATIVE REGIMENS TO CONTROL DM (7 marks)

A. Preoperative Assessment

• HbA1c - target <8% for Type 1, <7% for Type 2 (ADA); if >8% with severe hyperglycemia (>250 mg/dL), delay elective surgery
• Blood glucose (fasting and random)
• Serum electrolytes, creatinine/BUN (renal function)
• 12-lead ECG (silent myocardial ischemia is common due to autonomic neuropathy)
• Check for end-organ damage: retinopathy, nephropathy, neuropathy, cardiovascular disease

B. Management of Oral Hypoglycemic Agents

C. Insulin Regimens

• Must never stop basal insulin - even when fasting, to prevent DKA
• Reduce basal (long-acting: glargine/detemir) by 50% the night before or morning of surgery
• Hold rapid-acting/short-acting insulin while NPO (no carbohydrate intake to cover)
• If blood glucose >180 mg/dL preoperatively, give a correction dose of rapid-acting insulin per sliding scale

• Reduce evening long-acting insulin dose by 50-80% the night before
• Hold morning dose of short-acting insulin if NPO
• Check blood glucose on arrival; if >180 mg/dL, give supplemental rapid-acting insulin per sliding scale

1. Basal-Bolus Regimen - Long-acting insulin (glargine once daily) + rapid-acting insulin (lispro/aspart) with meals + correction sliding scale. Most physiological regimen; preferred for inpatients.
2. NPH + Regular (Split-Mixed) Regimen - Twice-daily NPH (intermediate-acting) + regular insulin before breakfast and dinner. Traditional approach; less flexible.
3. Sliding Scale Insulin (SSI) alone - Reactive correction based on blood glucose readings. Not recommended as sole therapy - inadequate and unpredictable.
4. Continuous Subcutaneous Insulin Infusion (CSII - Insulin Pump) - Delivers continuous basal short-acting insulin + meal boluses. For short procedures, the pump can be continued; for major/longer surgery, switch to IV insulin infusion.

• Schedule surgery first case of the day to minimize fasting duration
• Check blood glucose on arrival to preop area
• If BG <70 mg/dL: administer IV dextrose
• If BG >180 mg/dL: supplemental rapid-acting insulin
• Hold all oral agents; continue basal insulin at reduced dose (Type 1) or hold (Type 2)

3. PATIENT WITH UNCONTROLLED DM POSTED FOR EMERGENCY EXPLORATORY LAPAROTOMY - INTRAOPERATIVE GLUCOSE MANAGEMENT (10 marks)

A. The Problem

• Release of stress hormones (cortisol, catecholamines, glucagon, growth hormone)
• Inhibition of insulin secretion
• Increased hepatic gluconeogenesis and glycogenolysis
• Peripheral insulin resistance

B. Target Blood Glucose Intraoperatively

C. Methods to Control Intraoperative Glucose

1. Intravenous Insulin Infusion (Preferred for Major Surgery)

• Regular insulin (short-acting) 50 units in 50 mL normal saline = 1 unit/mL concentration
• Administer via syringe pump through a dedicated IV line (side port)

Units/hour = Plasma glucose (mg/dL) ÷ 150

• Adjust infusion rate hourly based on point-of-care glucose measurement
• Target: maintain BG between 140-180 mg/dL (ADA) or 85-180 mg/dL (Morgan & Mikhail)

• Give separate IV glucose (5% dextrose at 1-1.5 mL/kg/h) to prevent hypoglycemia and provide substrate (do NOT use glucose as the maintenance fluid)
• Use a separate isotonic non-glucose solution (e.g. Ringer's lactate or normal saline) for volume replacement and intraoperative losses
• Add 20 mEq KCl per liter to maintenance fluids as insulin drives potassium intracellularly

2. Subcutaneous Sliding Scale Insulin (For Short/Minor Procedures)

• Appropriate only for short, noninvasive operations in well-controlled diabetics
• Administer short-acting (regular) insulin SC per sliding scale based on glucose levels
• Half the usual morning NPH dose SC preoperatively + D5W infusion at 1.5 mL/kg/h
• Intraoperative hyperglycemia (>180 mg/dL) treated with IV regular insulin boluses
• 1 unit regular insulin IV lowers BG by approximately 25-30 mg/dL in a 70 kg adult
• Not suitable for emergency laparotomy (unpredictable absorption)

3. Glucose-Insulin-Potassium (GIK) Infusion

• Combined infusion containing glucose + insulin + potassium in a single bag
• Historically used; less flexible because adjusting insulin requires changing the entire bag
• Concurrent separate infusions of insulin and glucose are preferred as they are more easily adjusted independently

4. Blood Glucose Monitoring Protocol

• Measure blood glucose every 1 hour during IV insulin infusion
• Use bedside point-of-care glucometer (or arterial blood gas analyzer if arterial line present)
• If BG <85 mg/dL (hypoglycemia): stop insulin infusion, give 50 mL of 50% dextrose (D50W) IV - each mL of 50% dextrose raises BG by ~2 mg/dL in a 70 kg patient
• Document all readings and infusion rate adjustments
• All signs of hypoglycemia are masked under general anesthesia -- diaphoresis, tachycardia, confusion are absent; monitoring is the only protection

5. Anesthetic Considerations Specific to Uncontrolled Diabetics

• Airway: Assess for "prayer sign" (stiff joint syndrome due to glycosylation) - inability to oppose palms may predict difficult intubation
• Gastroparesis: Diabetic autonomic neuropathy causes delayed gastric emptying; treat as full stomach (rapid sequence induction, metoclopramide + antacid preoperatively)
• Autonomic neuropathy: Risk of post-induction hypotension; have vasopressors ready
• Fluid management: Avoid dextrose-containing fluids as primary maintenance; use balanced salt solutions
• Renal function: Monitor urine output; adjust fluid and drug dosing if nephropathy present
• Wound care: Strict aseptic technique throughout; hyperglycemia promotes SSI

6. Summary Algorithm for Intraoperative Management

On arrival to OT → Check BG
    BG <70 mg/dL → IV Dextrose 50% (25 mL), recheck in 15 min
    BG 70-180 mg/dL → Hourly monitoring, no insulin correction needed
    BG 180-250 mg/dL → Start IV insulin infusion (BG÷150 units/hr)
                        + D5W 1 mL/kg/hr separately
    BG >250 mg/dL → Start insulin infusion, check ketones
                     Give 10 units IV bolus regular insulin, then infusion
                     Monitor electrolytes (K+, Na+)
    
Intraoperatively → Check BG every 1 hour
                → Titrate insulin infusion to keep BG 140-180 mg/dL
                → Add 20 mEq KCl per litre of maintenance fluid
                → Continue through postoperative period in ICU

Summary Table

• Barash, Cullen & Stoelting's Clinical Anesthesia, 9e - Perioperative Glucose Management, pp. 1780-1782
• Morgan & Mikhail's Clinical Anesthesiology, 7e - pp. 1412-1415
• Current Surgical Therapy, 14e - Perioperative Glycemic Control, pp. 1571-1573

Uncontrolled Diabetes Mellitus Posted for Perianal Abscess - 20 Mark Answer

INTRODUCTION

PART 1: PERIANAL ABSCESS - SURGICAL OVERVIEW (4 marks)

Definition and Pathogenesis

Why Diabetics Are Uniquely Vulnerable

• Inhibits neutrophil chemotaxis and phagocytosis
• Impairs vascular reactivity (via angiotensin II and nitric oxide synthase pathways)
• Increases vascular permeability and platelet/leukocyte activation
• Peripheral neuropathy reduces pain sensation, delaying presentation
• Microangiopathy reduces tissue perfusion, impairing healing

Classification of Anorectal Abscesses (Parks Classification)

Surgical Principle

PART 2: PREOPERATIVE ASSESSMENT AND OPTIMIZATION (5 marks)

A. Clinical Assessment

• Type, duration, and current treatment of DM (Type 1 vs. Type 2, oral agents vs. insulin)
• HbA1c and recent blood glucose values
• Duration and severity of abscess (onset, fever, spreading cellulitis, crepitus)
• End-organ damage: nephropathy, neuropathy, retinopathy, cardiovascular disease
• Current medications (including anticoagulants, antihypertensives, SGLT2 inhibitors)
• Last oral intake (NPO status) - critical for airway management, especially with diabetic gastroparesis

• Vital signs: fever (>38.5°C suggests systemic sepsis), tachycardia, BP
• Assess extent of abscess: localised fluctuant swelling vs. spreading cellulitis, crepitus (gas = necrotising fasciitis!)
• Airway: prayer sign (inability to oppose palms flat) - suggests stiff joint syndrome from glycosylation, predicting difficult intubation
• Autonomic neuropathy signs: orthostatic hypotension, resting tachycardia, absent heart rate variability

B. Investigations

C. Management of Uncontrolled DM Before Surgery

• Target BG: 140-180 mg/dL before surgery
• If BG >250 mg/dL: Start IV regular insulin infusion (concentration 1 unit/mL in NS); titrate to bring BG to acceptable range
• Check and correct ketones (if DKA: must treat DKA first before proceeding to theatre - see below)

• Hypokalaemia (from vomiting, insulin therapy) must be corrected before anaesthesia (risk of cardiac arrhythmia)
• Target K+ >3.5 mEq/L

• Hold all oral hypoglycaemic agents (especially SGLT-2 inhibitors - risk of euglycaemic DKA; metformin - risk of lactic acidosis)
• Type 1 DM: Continue basal insulin at 50% dose - never omit, to prevent DKA
• Type 2 DM on insulin: Hold morning dose of short-acting insulin; reduce basal by 50%
• If septic/feverish: higher insulin requirements expected due to stress hyperglycaemia

D. Special Consideration: DKA

• BG >250 mg/dL + ketonuria/ketonaemia + metabolic acidosis (pH <7.3, HCO3 <18)

• IV fluid resuscitation: 0.9% saline 1L over 1 hour (correct dehydration)
• IV insulin infusion: 0.1 units/kg/hour regular insulin
• Potassium replacement: 20-40 mEq/L KCl per litre once K+ <5.5 mEq/L
• Monitor BG hourly, electrolytes 2-hourly
• Surgery once pH >7.3, HCO3 >15, BG <250 mg/dL, and patient haemodynamically stable

PART 3: ANAESTHETIC MANAGEMENT (6 marks)

Choice of Anaesthesia

• Position: Lithotomy (standard for perianal surgery)
• Spinal drug: Hyperbaric bupivacaine 0.5% (heavy) - 1.2-1.5 mL (6-7.5 mg) with or without fentanyl 25 mcg
• Target block level: T10 (umbilicus) - adequate for perineal surgery

• Treat as full stomach (diabetic gastroparesis = delayed gastric emptying)
• Rapid Sequence Induction (RSI): preoxygenate → cricoid pressure → propofol + suxamethonium IV → intubate
• Premedication: ranitidine/pantoprazole + metoclopramide (reduces aspiration risk)
• Maintenance: isoflurane/sevoflurane + O2/air; avoid N2O
• Airway: prepare for difficult intubation (prayer sign, glycosylation), have video laryngoscope available

Key Anaesthetic Concerns in Diabetic Patient

1. Difficult airway - stiff joint syndrome (glycosylation of temporomandibular + atlanto-occipital joints); always prepare for failed intubation
2. Gastroparesis - aspiration risk even if apparently NBM; treat as full stomach
3. Autonomic neuropathy - cardiovascular instability; post-induction hypotension; have vasopressors (ephedrine/phenylephrine) drawn up
4. Hypoglycaemia masked under GA - only monitoring protects the patient
5. Cardiovascular disease - silent myocardial ischaemia; monitor ECG
6. Renal impairment - adjust drug doses (e.g. avoid NSAIDs postoperatively)

PART 4: INTRAOPERATIVE GLUCOSE MANAGEMENT (3 marks)

Target

Protocol for Perianal Abscess I&D (Short Procedure)

• Hourly glucose monitoring
• No insulin correction typically needed for this short duration
• Sliding scale SC regular insulin if BG creeps above 180 mg/dL

• Give correction dose rapid-acting insulin SC (per sliding scale)
• Hourly BG monitoring throughout
• 1 unit regular insulin IV lowers BG by ~25-30 mg/dL in a 70 kg adult

• Start IV insulin infusion: Regular insulin in 0.9% NS (1 unit/mL)
• Starting rate = Plasma glucose (mg/dL) ÷ 150 = units/hour
• Give separately from IV dextrose; do NOT co-infuse in same line
• Concurrent D5W at 1 mL/kg/h to prevent hypoglycaemia
• Add 20 mEq KCl per litre of maintenance IV fluid (insulin drives K+ intracellularly)
• Check BG every 30-60 minutes

• Under spinal: patient may report sweating, anxiety (detectable)
• Under GA: all symptoms masked - monitoring is the only safeguard
• Treatment: stop insulin infusion, give 25-50 mL of 50% dextrose (D50W) IV - each mL raises BG by ~2 mg/dL in a 70 kg patient

PART 5: POSTOPERATIVE MANAGEMENT (2 marks)

Glucose Control

• Check BG on arrival to recovery and every 1-2 hours
• Continue IV insulin infusion if BG >180 mg/dL or if patient cannot take orally
• Transition to SC basal-bolus regimen once oral intake resumes (usually same day for perianal I&D)
• Resume usual antidiabetic medications when eating normally (restart metformin when renal function confirmed)
• Restart SGLT2 inhibitors only after fully oral intake re-established

Wound Care and Antibiotics

• Antibiotics: Not routinely required after simple I&D of perianal abscess in immunocompetent patients. However, in uncontrolled diabetics, give broad-spectrum antibiotics:
  • Co-amoxiclav (amoxicillin-clavulanate) OR
  • Metronidazole + cephalosporin (to cover anaerobes, Gram-negatives, and skin flora)
  • If MRSA risk: add vancomycin
  • Duration: 5-7 days (longer if spreading cellulitis or sepsis)
• Sitz baths from the next day - promotes drainage and hygiene
• Strict aseptic wound care - hyperglycaemia impairs wound healing and promotes SSI
• Watch for Fournier's gangrene - spreading pain, crepitus, foul odour = surgical emergency requiring radical debridement

Optimise DM Long-Term

• Endocrinology referral for optimisation of DM control
• Target HbA1c <7% (Type 2) / <8% (Type 1) before any future elective surgery
• Patient education on glucose monitoring, foot care, recognition of infections early

SUMMARY TABLE

• Barash, Cullen & Stoelting's Clinical Anesthesia, 9e - Perioperative Glucose Management, pp. 1780-1782
• Morgan & Mikhail's Clinical Anesthesiology, 7e - Anesthetic Considerations in Diabetes, pp. 1410-1415
• Current Surgical Therapy, 14e - Perioperative Glycaemic Control, pp. 1571-1573
• Schwartz's Principles of Surgery, 11e - Perianal Abscess, p. 1342
• Goldman-Cecil Medicine - Perianal Abscess: Epidemiology and Management, p. 1534
• Fischer's Mastery of Surgery, 8e - Drainage of Perianal Abscess, p. 4250