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DNB FINAL ANAESTHESIA — FAT PAPER 2

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Q1. Pain Management After Right Total Knee Replacement (TKR) in a 50-year-old Lady (10 marks)

Introduction

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Modes of Pain Management

A. Regional Anaesthesia Techniques

B. Systemic Analgesics (Multimodal)

• Paracetamol 1 g IV/oral Q6H (scheduled, not PRN)
• NSAIDs/COX-2 inhibitors — celecoxib, etoricoxib (reduce opioid consumption 30–40%)
• Gabapentinoids — pregabalin/gabapentin (pre-emptive analgesia, reduces central sensitization)
• Opioids — oral tramadol, morphine PCA; minimised in MMA
• Dexamethasone — 8 mg IV single dose reduces pain, PONV, and swelling
• Ketamine (sub-anaesthetic dose, 0.25–0.5 mg/kg IV) — NMDA antagonism reduces central sensitization

C. Non-Pharmacological

• Cryotherapy — ice packs reduce swelling and pain
• TENS (Transcutaneous electrical nerve stimulation)
• Elevation and physiotherapy

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Detailed Discussion: Adductor Canal Block (ACB)

• The adductor canal (Hunter's canal) is an aponeurotic tunnel in the mid-thigh
• Contains: Saphenous nerve, nerve to vastus medialis, medial femoral cutaneous nerve, femoral artery and vein
• Covers anterior and medial knee pain

1. Patient supine, hip externally rotated
2. High-frequency linear probe at mid-thigh
3. Identify femoral artery in the adductor canal deep to the sartorius muscle
4. Inject 15–20 mL of 0.25–0.375% ropivacaine or 0.25% bupivacaine adjacent to the saphenous nerve
5. Can place continuous catheter for 48–72 h infusion (ropivacaine 0.2% at 5–8 mL/h)

• Motor-sparing → quadriceps strength preserved → early ambulation Day 0/1
• Reduced fall risk compared to FNB
• Can be combined with LIA and IPACK block (infiltration between popliteal artery and knee capsule) for complete coverage
• Suitable for day-case TKR
• Low risk of systemic toxicity

• Covers only anterior/medial knee; misses posterior compartment → must combine with IPACK or sciatic block
• Technically more demanding than FNB
• Catheter dislodgement possible
• Does not cover tourniquet pain (requires GA/spinal)

• Pre-op: Celecoxib 400 mg + pregabalin 150 mg + paracetamol 1 g oral
• Intra-op: Spinal anaesthesia + ACB (ultrasound-guided) + LIA by surgeon + dexamethasone 8 mg IV
• Post-op: Paracetamol 1 g Q6H + etoricoxib 90 mg OD + oral tramadol PRN + ACB catheter infusion + cryotherapy

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Q2. Pre-operative Assessment and Optimization of a Morbidly Obese Female for Gastric Bypass Surgery (10 marks)

Definition

Pre-operative Assessment

History

• Duration and degree of obesity (BMI, weight, height)
• Comorbidities: T2DM, HTN, OSA, IHD, GORD, hypothyroidism, depression
• Medications: antihypertensives, OHAs/insulin, CPAP use, anticoagulants
• Previous anaesthesia: difficult airway, failed intubation, PONV
• Exercise tolerance and functional capacity (METs)
• History of snoring, daytime somnolence (STOP-BANG score for OSA)

Physical Examination

• Airway: Mallampati (likely Class III/IV), short thick neck, limited mouth opening, reduced cervical mobility — predict difficult intubation
• Cardiovascular: BP (both arms), signs of RVF (JVD, oedema, cor pulmonale)
• Respiratory: SpO₂ on room air, breath sounds, use of accessory muscles
• Abdomen: Hiatal hernia, GORD symptoms (high aspiration risk)
• Peripheral IV access: Difficulty anticipated — central line may be needed

Systemic Evaluation

Investigations

• Routine: CBC, RFT, LFT, electrolytes, blood glucose, HbA1c, urine RE
• Cardiac: ECG (LVH, AF, RBBB), 2D Echo if symptomatic (EF, PAP, wall motion)
• Respiratory: Spirometry (obstructive vs restrictive), ABG (CO₂ retention in OHS), overnight polysomnography if OSA suspected
• Airway: Neck circumference, thyromental distance, lateral neck X-ray
• Others: Coagulation profile (pre-heparin VTE prophylaxis planned)

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Pre-operative Optimization

1. Respiratory Optimization

• OSA: Ensure patient is on CPAP/BiPAP; continue until morning of surgery
• OHS: Pre-op NIV (BiPAP) for 2–4 weeks reduces CO₂, improves lung function
• Chest physiotherapy and incentive spirometry pre-operatively
• If SpO₂ < 90% on room air — optimise before elective surgery

2. Cardiovascular Optimization

• Control hypertension (target BP < 140/90)
• Treat AF (rate/rhythm control)
• Pulmonary HTN: refer to cardiologist if PAP > 55 mmHg
• Continue antihypertensives up to morning of surgery (except ARBs/ACEi — risk of intra-op hypotension)

3. Metabolic Optimization

• Diabetes: Target HbA1c < 8% for elective surgery; perioperative glucose 6–10 mmol/L
• Insulin sliding scale; stop SGLT-2 inhibitors 3–4 days pre-op (euglycaemic DKA risk)
• Hypothyroidism: Ensure euthyroid (TSH normal)

4. Thromboprophylaxis

• Enoxaparin 40–60 mg SC OD started night before; TED stockings; pneumatic compression devices

5. GI Prophylaxis

• Ranitidine/PPI the night before and morning of surgery
• Metoclopramide 10 mg pre-op (promotility)
• Rapid sequence induction planned — communicate to team

6. Airway Preparation

• Assess with Mallampati, LEMON score
• Plan for awake FOB intubation if predicted very difficult
• Ramped position (ear-to-sternal notch alignment) — improves laryngoscopy in obese
• Video laryngoscope and surgical airway as backup plan

7. Pre-operative Fasting and Pre-medication

• Standard 6 h solid, 2 h clear fluid (though high-risk aspiration — discuss with surgeon)
• Midazolam with caution (may precipitate respiratory depression/airway loss)
• Avoid IM injections (unpredictable absorption)

8. Pre-operative Weight Loss Programme

• In elective cases: 2-week VLCD (Very Low Calorie Diet) pre-op reduces liver size, improves surgical access
• Some centres mandate 10% weight loss before surgery

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Q3. Causes of Atrial Fibrillation (AF) and Its Management (10 marks)

Definition

Causes of AF

Cardiac Causes

Non-Cardiac Causes

Mnemonic: PIRATES

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Management of AF

1. Is patient haemodynamically stable?
2. Duration of AF (< 48 h or > 48 h / unknown)?
3. Rate vs Rhythm control strategy?

A. Acute Management of Haemodynamically Unstable AF

• Immediate DC Cardioversion — Synchronised 200 J biphasic
• Anticoagulate before if possible; if not, proceed immediately

B. Acute Management of Haemodynamically Stable AF

C. Anticoagulation

• CHA₂DS₂-VASc score guides decision:
  • Score 0 (male) / 1 (female): No anticoagulation
  • Score ≥ 2: Anticoagulate
• Agents: NOACs (rivaroxaban, apixaban, dabigatran) preferred over warfarin (INR 2–3)
• If AF > 48 h and cardioversion planned: anticoagulate for 3 weeks before and 4 weeks after OR TOE-guided cardioversion

D. Long-term / Definitive Management

• Catheter ablation (pulmonary vein isolation) — for paroxysmal AF refractory to drugs
• Surgical ablation (Maze procedure) — during concomitant cardiac surgery
• Left atrial appendage occlusion (Watchman device) — when anticoagulation contraindicated
• Treat underlying cause: thyroid, valve surgery, lifestyle modification, alcohol cessation

Perioperative AF Management

• Continue rate-control medications perioperatively
• If new AF develops intraoperatively → check electrolytes, oxygenation, anaemia
• Rate control with metoprolol or diltiazem; amiodarone if LV dysfunction
• Elective cardioversion post-operatively once stable

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Q4. FRC, CC, CV — Definitions, Diagram, and Factors Affecting FRC (10 marks)

Definitions

Functional Residual Capacity (FRC)

FRC = ERV (Expiratory Reserve Volume) + RV (Residual Volume) Normal FRC ≈ 2100–2400 mL (30 mL/kg in adults)

• Helium dilution (closed-circuit)
• Nitrogen washout (open-circuit)
• Body plethysmography (most accurate — measures all gas including trapped air)

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Closing Capacity (CC) and Closing Volume (CV)

CC = CV + RV

• Normal young adult: CC < FRC → airways stay open throughout tidal breathing → no V/Q mismatch
• Elderly, obese, supine position: CC > FRC → small airways close during normal tidal breathing → V/Q mismatch → hypoxaemia → atelectasis

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Lung Volume Diagram

       |
  TLC  |══════════════════════════════════════╗
       |                                       ║ IC
       |                                       ║
       |                          ┌────────────╫──── IRV
 ERV+  |    ┌──────────────────┐  │            ║
  TV   |    │  Tidal Breathing │══╧═══════════╗║
       |    └──────────────────┘              ║║← TV
       |                    ▼                 ║║
  FRC  |════════════════════════════════════╗ ╚╝ ← ERV
       |                                    ║
  CV   |-------- Closing Volume starts ─────║─ (in dependent zones)
  CC   |════════════════════════════════╗   ║
       |                                ║   ║
  RV   |════════════════════════════════╝   ╚═

  CC = CV + RV
  FRC = ERV + RV

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Factors Affecting FRC

Factors That DECREASE FRC

Factors That INCREASE FRC

Clinical Applications

• Pre-oxygenation works by denitrogenating the FRC oxygen store (replaces N₂ with O₂)
• Obese/pregnant patients desaturate rapidly because FRC is critically reduced
• PEEP restores FRC under anaesthesia, prevents atelectasis
• Recruitment manoeuvres open collapsed alveoli, temporarily restore FRC

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Q5. Anaesthetic Concerns — Obstructive Jaundice for Lap. Chole + CBD Exploration (10 marks)

Introduction

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Pathophysiology of Obstructive Jaundice

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Pre-operative Assessment and Concerns

1. Hepatic Dysfunction

• LFT: elevated bilirubin (conjugated), ALP, GGT; AST/ALT moderate rise
• Hepatocyte dysfunction → reduced synthesis of clotting factors (II, VII, IX, X — Vitamin K dependent)
• Coagulopathy: prolonged PT/INR → risk of intra-op bleeding
• Management: Vitamin K 10 mg IM/IV for 3 days pre-op → repeat PT; FFP if urgent surgery

2. Renal Dysfunction — Hepatorenal Syndrome (HRS)

• Bilirubin is directly nephrotoxic to renal tubules
• Endotoxaemia → renal vasoconstriction
• Risk of acute kidney injury (AKI) peri-operatively
• Pre-operative: Urine RE, serum creatinine, urea; ensure adequate hydration
• Peri-operative renal protection:
  • IV fluids: Normal saline or Ringer's lactate — maintain UO > 1 mL/kg/h
  • Mannitol 0.5 g/kg IV before biliary decompression
  • Oral lactulose pre-op (reduces gut endotoxin absorption)
  • Avoid NSAIDs, aminoglycosides

3. Cardiovascular

• Decreased SVR (vasodilatory effect of bile salts on vascular smooth muscle)
• Bradycardia (vagotonic effect of bile salts)
• Impaired response to vasopressors
• Pre-op: ECG, echocardiography if indicated; correct hypovolaemia

4. Haematological

• Anaemia (haemolysis), leukocytosis (if cholangitis)
• Thrombocytopaenia (if hepatic involvement)
• Cross-match and reserve 2–4 units blood

5. Gastrointestinal / Nutrition

• Malabsorption of fat-soluble vitamins (A, D, E, K)
• Malnutrition → impaired wound healing, immune suppression
• Pre-op nutritional supplementation

6. Sepsis / Cholangitis

• Ascending cholangitis (Charcot's triad: fever + jaundice + RUQ pain) — must be controlled pre-op
• Blood cultures + antibiotics (cefuroxime + metronidazole) before surgery

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Intra-operative Anaesthetic Management

Airway

• Standard RSI if cholangitis/full stomach suspected
• OGT tube after intubation for gastric decompression (laparoscopic surgery)

Anaesthetic Agents

• Induction: Propofol (hepatically metabolised but safe); reduce dose if encephalopathic
• Volatile agents: Isoflurane/sevoflurane preferred (less hepatotoxic; halothane is ABSOLUTELY contraindicated — causes hepatic necrosis)
• Muscle relaxants: Atracurium or cisatracurium preferred (Hofmann elimination — independent of hepatic/renal function); avoid pancuronium, vecuronium (hepatic metabolism)
• Opioids: Morphine undergoes hepatic conjugation (active metabolites accumulate); prefer fentanyl or remifentanil (ester hydrolysis, unaffected by liver disease)
• Avoid: halothane, high-dose paracetamol, tetracyclines, ketorolac

Monitoring

• Standard: SpO₂, ETCO₂, ECG, NIBP, temperature
• Invasive: Arterial line (beat-to-beat BP for haemodynamic instability), CVP line (fluid management)
• Urinary catheter mandatory — monitor UO hourly

Laparoscopic Concerns

• Pneumoperitoneum → ↑ IAP → ↑ portal pressure → hepatic blood flow ↓ by up to 40%
• Use minimum effective CO₂ pressure (≤12 mmHg)
• Maintain ETCO₂ < 40 mmHg (risk of hypercapnia worsened by splanchnic absorption)
• Keep MAP adequate for renal perfusion
• Position: Reverse Trendelenburg (reduces portal pressure, improves ventilation)

Fluid Management

• Avoid hypotension (causes hepatic and renal ischaemia)
• Avoid dextrose saline (worsens hyponatraemia, glucose intolerance)
• Balanced crystalloids (Ringer's lactate or PlasmaLyte) preferred
• Colloids/blood products as needed

Coagulopathy Management

• Have FFP, cryoprecipitate, platelets available
• Cell salvage may be used (not if malignancy)
• Tranexamic acid (TXA) 1 g IV

Pain Management

• Multimodal: paracetamol + opioids (careful dose adjustment) + regional (TAP block for open; epidural if coagulation allows)

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Post-operative Concerns

• Observe for AKI, bleeding, bile leak, cholangitis recurrence
• Jaundice may temporarily worsen post-op (hepatocyte ischaemia)
• ICU/HDU monitoring if severe preoperative jaundice (bilirubin > 200 μmol/L)
• Restart lactulose; prophylactic antibiotics for 5 days

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Q6. Anaesthetic Concerns — Post COVID Diabetic Female with Mucormycosis for Debridement Under GA (10 marks)

Background

• Poorly controlled T2DM (hallmark risk factor)
• High-dose corticosteroid use (COVID treatment)
• Immune dysregulation from SARS-CoV-2

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Multi-system Anaesthetic Concerns

1. Airway — Potentially Catastrophic

• Anticipate difficult airway — always plan for
• Awake Fibreoptic Intubation (AFOI) is the safest approach if mouth opening is restricted or anatomy is distorted
• If anatomy is reasonably preserved: video laryngoscope
• Have surgical airway (tracheostomy) on standby — surgeon must be in room during intubation
• Oral RAE tube or preformed tube to facilitate surgical access
• Throat pack to prevent blood/debris aspiration
• Suction must be immediately available

2. Metabolic — Diabetic Ketoacidosis (DKA) Risk

• Mucormycosis and fungal infection worsen hyperglycaemia → precipitates or worsens DKA
• Pre-op: Check blood glucose, HbA1c, ABG (exclude metabolic acidosis), ketones
• Target perioperative glucose: 6–10 mmol/L
• Insulin infusion protocol intra-operatively
• Avoid dextrose-containing IV fluids
• If DKA present: postpone elective surgery, correct fluid/electrolyte/acidosis first

3. Post-COVID Systemic Effects

• Pulmonary fibrosis/sequelae: Restrictive pattern, reduced DLCO, hypoxaemia on exertion
• Check pre-op SpO₂, spirometry, CXR/HRCT chest
• Anticipate difficulty ventilating (reduced compliance) — use lung-protective ventilation (TV 6–8 mL/kg IBW, PEEP 5–8 cmH₂O)
• COVID coagulopathy: Hypercoagulable state → DVT/PE risk; check D-dimer, PT, APTT
• Myocarditis/cardiac sequelae: Check ECG, troponin, ECHO if symptomatic
• Thrombocytopaenia: May co-exist

4. Antifungal Therapy — Amphotericin B Toxicity

• Nephrotoxicity: AKI, hypomagnesaemia, hypokalaemia, RTA type IV → Check RFT, electrolytes; correct K⁺ and Mg²⁺ before GA
• Infusion reactions: Fever, rigors, hypotension, bronchospasm during infusion
• Anaemia: Amphotericin causes dose-dependent anaemia → check Hb, cross-match blood
• Isavuconazole or posaconazole may also be used; fewer interactions with anaesthetic agents but check for QT prolongation (azoles → QTc prolongation)

5. Orbital/Cerebral Involvement

• If orbital exenteration planned: bleeding (orbital vasculature), oculocardiac reflex (vagal → bradycardia, arrest) → Have atropine IV immediately available; notify surgeon to pause if bradycardia < 40 bpm
• Cerebral involvement: raised ICP, seizures post-op; monitor neurological status
• Eye protection (contralateral eye) essential

6. Surgical and Positioning Concerns

• Procedure can be prolonged (extensive debridement)
• Significant intra-operative haemorrhage — cross-match 4–6 units pRBC; have vasopressors ready
• Head-up 20–30° position to reduce venous ooze and ICP
• Avoid neck flexion (risk of tracheal tube kinking)

7. Infection Control

• Mucormycosis is not directly contagious but immunocompromised nature demands aseptic precautions
• Consider PPE for OR team (risk of aerosolised fungal spores during debridement)

8. Anaesthetic Technique

• TIVA (propofol + remifentanil) preferred — avoids volatile agents that might depress cardiac function in a potentially compromised patient; also preferred if prolonged intubation/ICU planned
• Adequate depth essential (stimulating surgery)
• Avoid N₂O (risk of air embolism in sinuses, inhibits methionine synthase)
• Steroid coverage: If patient was on steroids for COVID → supplement with hydrocortisone 50–100 mg IV perioperatively (adrenal suppression)

9. Post-operative Plan

• Likely ICU/HDU admission post-operatively
• Continue antifungal therapy
• Strict glucose control (target 6–10 mmol/L)
• Airway oedema from surgical manipulation → plan post-op ventilation or delayed extubation
• Thromboprophylaxis (LMWH) given hypercoagulability

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Q7A. Impact Factor of a Journal (5 marks)

Definition

Formula

IF (year X) = Citations received in year X to articles published in years (X−1) and (X−2) / Total articles published in years (X−1) and (X−2)

IF 2024 = 1000 / 200 = 5.0

Significance

• High IF journals (e.g., NEJM: ~98, Lancet: ~60, Anesthesiology: ~7.5, BJA: ~8) indicate frequently cited, high-impact research
• Used to evaluate journal quality, guide submissions, and influence academic promotions/grants

Limitations of Impact Factor

Alternatives to Impact Factor

• h-index (Hirsch): number of papers (h) with at least h citations each — measures individual researcher output
• CiteScore (Elsevier/Scopus): uses 4-year window
• SCImago Journal Rank (SJR): weights citations by journal prestige
• SNIP (Source Normalized Impact per Paper): normalises for field-specific citation practices
• Altmetrics: social media, news, policy citations — captures real-world impact

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Q7B. Null Hypothesis and P-Value (5 marks)

Null Hypothesis (H₀)

There is no difference, no effect, and no association between the groups or variables being compared.

• H₀: "There is no difference in pain scores between drug A and drug B"
• H₁: "Drug A provides better pain relief than drug B"

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P-Value

A small p-value = the observed data is unlikely under H₀ = evidence against H₀.

• Statistical significance ≠ clinical significance: A drug may show p < 0.001 but only reduce BP by 1 mmHg — not clinically meaningful
• P-value does NOT tell you the size or direction of the effect → use confidence intervals (CI) alongside
• P-value is affected by sample size: very large samples can make trivial differences statistically significant
• It is a continuous measure of evidence, not a binary "significant/not significant" verdict

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Q8. Preparation for Awake Intubation — 18-year-old with TMJ Ankylosis for Surgery (10 marks)

Introduction

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Step-by-Step Preparation for Awake Intubation

Step 1: Pre-operative Airway Assessment

• Mouth opening: Often < 5 mm in bony ankylosis (knife-edge interincisal distance)
• Assess nasal patency (bilateral, deviated septum)
• Mallampati score (often impossible if mouth won't open)
• Neck extension, thyromental distance
• HRCT face/mandible: extent of bony ankylosis, assess nasal anatomy
• Plan: Nasal AFOI is almost always the route of choice in TMJ ankylosis

Step 2: Pre-operative Counselling and Consent

• Thorough explanation of the procedure in simple terms to the patient
• Explain why GA cannot be induced before securing airway
• Demonstrate the fibreoptic bronchoscope
• Address anxiety — this patient is 18 years old (young, cooperative)
• Written informed consent for the procedure

Step 3: Pre-medication (Night Before and Morning of Surgery)

Step 4: Equipment Preparation (SOAPME Mnemonic)

• S — Suction (two working suckers)
• O — Oxygen (nasal prongs delivering O₂ during scope + supplemental facemask)
• A — Airway: Fibreoptic bronchoscope (3.5–4 mm for nasal), NTT sizes 6.0/6.5/7.0, Airway exchange catheter
• P — Pharmacology: Local anaesthetics, sedation drugs, emergency drugs (atropine, adrenaline, succinylcholine for surgical airway)
• M — Monitors: SpO₂, ETCO₂, ECG, NIBP
• E — Extra: Surgeon present with tracheostomy tray open and ready

Step 5: Airway Topicalisation (Surface Anaesthesia — Most Critical Step)

• Co-phenylcaine spray (lignocaine 5% + phenylephrine 0.5%) — 2 puffs each nostril
• Or: Lignocaine 4% + xylometazoline on ribbon gauze, pack nostril for 5 min
• Lubricate nasal airway with 2% lignocaine gel; insert progressively larger nasal airways (5→7 mm) to dilate the passage

• Nebulised lignocaine 4% (4 mL over 15 min) — patient inhales through nose → coats entire airway (excellent technique, patient-friendly)
• Atomised lignocaine (MADgic or similar atomiser device) to oropharynx and posterior pharynx
• Trans-cricothyroid instillation (rarely needed in young patient if nebulisation is adequate): 2 mL of 4% lignocaine injected through cricothyroid membrane at end of expiration → patient coughs → distributes throughout trachea and larynx
• Superior laryngeal nerve block (bilateral): 2 mL of 2% lignocaine injected just below the greater cornu of thyroid cartilage — blocks internal branch → anaesthetises epiglottis, aryepiglottic folds, vocal cords (above)

Step 6: Sedation (Maintain Consciousness and Cooperative Patient)

Step 7: Fibreoptic Intubation Procedure

1. Pre-load NTT (size 6.5 for 18M, 6.0 for female) on the bronchoscope; warm in saline
2. Pass scope through the more patent nostril (pre-determined by examination and CT)
3. Navigate: floor of nose → inferior meatus → nasopharynx → identify uvula, epiglottis → pass between cords
4. Confirm tracheal position (visualise carina)
5. Slide NTT over scope into trachea
6. Confirm placement with bilateral breath sounds + ETCO₂ capnograph waveform
7. Induce GA only after tube is confirmed in trachea (propofol or inhalational)

Step 8: Failure Plan / Backup

• If AFOI fails: attempt second nostril
• Video laryngoscope + topicalisation for oral approach
• Surgical airway (awake tracheostomy under LA) — surgeon must be scrubbed and ready
• Never attempt blind nasal intubation in complete ankylosis

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Q9A. Target Controlled Infusion (TCI) (5 marks)

Definition

Pharmacokinetic Basis

• Central compartment (V₁): Plasma/blood (where drug is administered and measured)
• Peripheral compartment 1 (V₂): Rapidly equilibrating tissues (heart, liver, kidneys)
• Peripheral compartment 2 (V₃): Slowly equilibrating tissues (muscle, fat)

Common PK Models

Clinical Use of TCI

• TIVA (Total Intravenous Anaesthesia): Propofol TCI (target Cp 4–6 mcg/mL induction; 3–4 mcg/mL maintenance) + remifentanil TCI
• Sedation: Propofol Ce target 0.5–2 mcg/mL
• Allows rapid titration — change target → pump calculates new rate automatically

Advantages of TCI

• More predictable drug concentrations than manual infusions
• Smooth induction and maintenance — avoids bolus peaks and troughs
• Rapid recovery (especially with remifentanil) — predictable offset
• Facilitates BIS/depth of anaesthesia monitoring — can correlate Ce with clinical effect
• Allows simultaneous opioid + hypnotic titration
• Useful in elderly, obese, critically ill — select appropriate model
• Reduces drug waste and total drug consumption

Limitations/Disadvantages

• Not approved by FDA in USA (CE marked in Europe, approved in India/UK)
• Accuracy depends on which PK model is used — no single model fits all patients
• Obese patients: standard models often inaccurate (need obesity-specific models: eleveld, cortinez)
• Children: special paediatric models required (Paedfusor for propofol)
• Requires expensive dedicated pump and software
• TIVA failure: no airway warning (unlike volatile agent — no agent monitor); must use BIS
• Cannot directly measure plasma concentration at bedside

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Q9B. Organophosphate (OP) Poisoning (5 marks)

Introduction

Mechanism

1. Muscarinic receptors (smooth muscle, glands, heart)
2. Nicotinic receptors (NMJ, autonomic ganglia)
3. CNS (muscarinic + nicotinic)

Clinical Features

• Muscle fasciculations → weakness → paralysis (including respiratory muscles)
• Tachycardia, hypertension (ganglionic)
• Mydriasis (ganglionic nicotinic may override muscarinic miosis in severe cases)

• Anxiety, agitation, seizures, coma, respiratory depression

Management

Immediate (ABC Priority)

1. Remove from exposure — decontaminate (remove clothing, wash skin with soap and water)
2. Airway: High-flow O₂; early intubation if GCS ↓, respiratory failure, or excessive secretions
3. IV access — blood for RBC cholinesterase levels (confirms diagnosis; severity guide)

Specific Antidotes

• Mechanism: Competitive antagonist at muscarinic receptors → reverses secretions, bronchospasm, bradycardia
• Dose: 2–4 mg IV bolus every 5–10 min, then infusion as needed
• Titrate to drying of secretions (end-point), NOT pupil size or HR
• Severe cases may require hundreds of mg over hours (auto-injectors in mass casualty)
• Atropine does NOT reverse nicotinic features (muscle weakness/paralysis)

• Mechanism: Reactivates AChE before "aging" by cleaving OP-enzyme bond → restores AChE function
• Effective only if given early (before aging; within 24–48 h for most OPs; sarin ages in minutes)
• Dose: 1–2 g IV over 15–30 min, then 500 mg/h infusion for 24–48 h
• Reverses nicotinic features (weakness, fasciculations) which atropine cannot
• Caution: Rapid IV administration → cholinergic crisis, hypertension, cardiac arrest — give slowly

• For seizures: Diazepam 10 mg IV or midazolam 0.1 mg/kg
• Also reduces CNS excitability

Supportive Management

• Ventilatory support (IPPV) if respiratory failure
• Bronchodilators for bronchospasm (salbutamol)
• Avoid succinylcholine (AChE inhibitor: OP prolongs its action → prolonged apnoea) — use rocuronium
• Avoid morphine, aminoglycosides (respiratory depressants)
• Cardiac monitoring (QTc prolongation, torsades possible)
• Seizure control, temperature management

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Q10A. TURP Syndrome (5 marks)

Definition

Irrigating Fluids and Why They Cause Hyponatraemia

• Glycine 1.5% (most common; hypotonic, 220 mOsm/L vs. plasma 285)
• Sorbitol 3.3% / Mannitol 5% / Distilled water
• Bipolar TURP → normal saline can be used → eliminates TURP syndrome risk

Pathophysiology

• ↑ intravascular volume → hypervolaemia → pulmonary oedema
• Dilution of plasma Na⁺ → hyponatraemia → cerebral oedema, neurological symptoms
• Glycine toxicity: glycine is an inhibitory neurotransmitter → visual disturbances (transient blindness — "glycine retinopathy")
• Glycine metabolised to ammonia → hyperammonaemia → encephalopathy

Clinical Features by Severity

Risk Factors

• Resection time > 60 min
• Gland weight > 45 g
• Irrigation fluid height > 60 cm
• Venous bleeding (indicates open venous sinuses)
• Capsular perforation

Why Spinal Anaesthesia is Preferred for TURP

• Patient is awake → early detection of TURP syndrome symptoms (confusion, restlessness)
• Reduces blood loss
• Allows assessment of mental status intra-operatively

Treatment

1. Stop the procedure immediately (inform surgeon)
2. Loop diuretic: Furosemide 40–80 mg IV → promotes free water excretion
3. Correction of hyponatraemia:
   • Mild/moderate (Na > 120): Fluid restriction + furosemide + allow spontaneous correction
   • Severe/symptomatic (Na < 120 with seizures): Hypertonic saline (3%) cautiously
   • Rate of correction: ≤ 0.5 mEq/L/h, maximum 8–10 mEq/L in 24 h (to prevent central pontine myelinolysis — CPM)
4. Treat seizures: Benzodiazepines (not phenytoin — less effective in hyponatraemic seizures)
5. Pulmonary oedema: Diuresis, O₂, CPAP/intubation if severe

Prevention

• Limit resection to < 60 min
• Keep irrigation bag < 60 cm above patient
• Use bipolar TURP (saline irrigation) or laser enucleation (HoLEP) — virtually eliminates TURP syndrome
• Monitor Na⁺ every 30 min in prolonged procedures

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Q10B. Prevention of Hypothermia in a Neonate Posted for Emergency Laparotomy (5 marks)

Why Neonates Are Uniquely Vulnerable to Hypothermia

• Coagulopathy
• Metabolic acidosis
• Hypoglycaemia (depletes BAT)
• Pulmonary hypertension (cold → vasoconstriction → ↑ PVR)
• Delayed drug metabolism → prolonged effect of anaesthetic agents
• Increased O₂ consumption (on arousal) → apnoea and bradycardia
• Poor wound healing

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Prevention Strategies (Comprehensive)

A. Pre-operative

• Keep neonate in incubator until transfer to OR
• Delay surgery only to stabilise temperature if possible
• Warm the OR: Increase ambient temperature to 26–28°C before baby arrives
• Warm blankets around non-operative areas
• Pre-warm all IV fluids

B. During Transport

• Wrap in warm blankets or plastic wrap (polyethylene bag for premature neonates)
• Use transport incubator (servo-controlled)

C. Intraoperative Prevention

D. Pharmacological

• Dexmedetomidine — reduces shivering threshold; can paradoxically reduce heat loss by preventing vasoconstriction-mediated redistribution
• Avoid excess neuromuscular blockade if spontaneous breathing/thermogenesis needed post-op

E. Post-operative

• Warm recovery room (26°C)
• Place back in incubator/servo-controlled cot immediately
• Warm blankets; skin-to-skin if condition allows

F. Monitoring

• Continuous core temperature monitoring is mandatory:
  • Rectal: most accessible for core temp in neonate
  • Oesophageal: gold standard for core temp but requires intubation
  • Axillary (skin): convenient but underestimates core by 0.5–1°C
• Target: 36.5–37.5°C — active warming continues until end of procedure

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