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AS4.1-7 | General Anaesthesia — PBL Case

CLINICAL SETTING

Mr Gopal is a 58-year-old male labourer who presents to the emergency department at 11 PM with a 36-hour history of colicky central abdominal pain, absolute constipation, and repeated vomiting. He is haemodynamically compensated on arrival (BP 162/96 mmHg, HR 102/min, RR 20/min, SpO₂ 96% on air, temperature 37.8°C). He appears mildly dehydrated — dry oral mucosa, reduced skin turgor. He last ate a full meal approximately 4 hours ago and last drank fluid (water) 2 hours ago. His past medical history includes hypertension (poorly controlled; on amlodipine 5 mg OD, currently without an antihypertensive for the past 2 weeks because he ran out of tablets), type 2 diabetes on diet control, and a 30-pack-year smoking history with mild exertional dyspnoea. He has no prior surgeries. He has no known drug allergies. On examination his abdomen is distended and tympanitic with visible peristalsis. CT scan confirms small bowel obstruction with no evidence of ischaemia or perforation. The surgical team requests urgent laparotomy. You are the anaesthesia resident called to assess Mr Gopal for general anaesthesia. As you examine his airway, you note: mouth opening 3.5 cm, thyromental distance 5.8 cm, short muscular neck with limited extension (approximately 30°), and on pharyngeal examination with maximal mouth opening and tongue out, only the soft palate base is visible — the uvula and fauces are not seen.

Trigger 1: Airway and Risk Assessment

You complete Mr Gopal's pre-operative assessment. Relevant findings: weight 82 kg; BMI 29.8; haemoglobin 13.4 g/dL; serum sodium 134 mmol/L, potassium 3.2 mmol/L; creatinine 118 µmol/L; blood glucose 9.4 mmol/L; ECG shows sinus tachycardia with no ischaemic changes; chest X-ray: mildly hyperinflated lungs. His BP on repeated measurement is 158/94 mmHg.

DISCUSSION POINTS

  • Assign Mr Gopal an ASA physical status classification (I–VI with E suffix for emergency) with justification for each component. Clearly distinguish between ASA grading (systemic disease) and Mallampati grading (oropharyngeal view for airway prediction).
  • Classify his Mallampati grade based on the pharyngeal findings described. Given his Mallampati grade, thyromental distance (5.8 cm), limited neck extension, and BMI, what is your prediction of laryngoscopic difficulty? Which additional bedside test would you perform to complete your airway assessment?
Click to reveal Trigger 2: Induction Strategy and Pharmacology (discuss previous trigger first!)

Trigger 2: Induction Strategy and Pharmacology

You determine that Mr Gopal requires rapid-sequence induction (RSI) because he has a full stomach (ate 4 hours ago; last fluid 2 hours ago — does not meet the 2-hour clear fluid fasting rule) and has vomited repeatedly, placing him at high risk for pulmonary aspiration. The anaesthetic machine has been checked. Drugs prepared include propofol, suxamethonium, fentanyl, atropine, ephedrine, and a failed-airway cart is at the bedside. His hypertension is acknowledged but the surgical team judges that delay is not safe.

DISCUSSION POINTS

  • Calculate the induction dose of propofol for Mr Gopal (weight 82 kg) in mg/kg and as an actual dose. Is propofol the optimal choice in a patient with a BP of 158/94 mmHg and moderate haemodynamic risk? Justify your choice or suggest an alternative, naming its dose per kg.
  • Describe the RSI technique step by step for Mr Gopal: preoxygenation target, role of cricoid pressure, dose of suxamethonium per kg, what you will do if you cannot intubate on the first attempt. Why is neostigmine not given to reverse suxamethonium if intubation fails and the block must be continued?
Click to reveal Trigger 3: Intraoperative Crisis and Monitoring (discuss previous trigger first!)

Trigger 3: Intraoperative Crisis and Monitoring

Mr Gopal is successfully intubated on the second attempt using a bougie after a Cormack-Lehane Grade III view at first laryngoscopy. Surgery commences and laparotomy reveals an adhesive band causing small bowel obstruction; a small bowel resection is performed. Forty-five minutes into the procedure, the following monitoring data are noted: BP 88/52 mmHg (was 125/80 mmHg 10 minutes ago), HR 118/min, ETCO₂ 42 mmHg (was 36 mmHg), SpO₂ 97%, the BIS monitor now reads 62 (was 47 during maintenance). The volatile agent concentration is 0.9 MAC. Blood loss is estimated at 600 mL in the suction container. The anaesthesiologist notes that the IV infusion bag ran empty 5 minutes ago.

DISCUSSION POINTS

  • List the three most likely causes of this acute hypotension in order of priority given the available monitoring data. What specific monitoring information (including BIS value, ETCO₂ trend, and blood loss estimate) helps you rank these causes? What immediate steps will you take in the next 2 minutes?
  • The BIS has risen to 62 while the MAC is 0.9. Does this mean the patient is at risk of awareness? How do you respond? What are the minimum monitoring standards you should be maintaining throughout this procedure, and what does capnography specifically tell you in this clinical context?

Group Task Assignments

Group 1: Collaborative Task

  • Construct a structured difficult airway algorithm for Mr Gopal starting from the decision to intubate through 'cannot intubate, cannot oxygenate' (CICO): use the ASA/DAS framework. Include at least three rescue strategies in sequence and identify when a surgical airway (cricothyrotomy) is indicated.

Group 2: Collaborative Task

  • Design a post-operative care plan for Mr Gopal covering: (1) extubation criteria and timing; (2) multimodal analgesic regimen (state specific agents and doses per kg); (3) monitoring parameters in the recovery room; (4) early warning criteria that would require critical care admission. Present this as a structured handover document as if handing over to the recovery nurse.

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [AS4.2] What are the components of the LEMON airway assessment (Look, Evaluate 3-3-2 rule, Mallampati, Obstruction, Neck mobility) and how does each component apply to Mr Gopal? What bedside tools are available when direct laryngoscopy fails (bougie, video laryngoscopy, LMA, intubating LMA, surgical airway)?
  2. [AS4.1] What are the pharmacological differences between depolarising (suxamethonium) and non-depolarising (rocuronium, vecuronium) neuromuscular blocking agents in terms of mechanism, onset, duration, reversal, and contraindications? When is each class preferred?
  3. [AS4.3] What are the steps of rapid-sequence induction, and why is each step necessary? What modifications are made for a patient with haemodynamic instability? What are the absolute contraindications to cricoid pressure?
  4. [AS4.5] What is the clinical significance of the bispectral index (BIS) value of 62? What is the target BIS range for surgical anaesthesia? At what BIS level is there risk of awareness, and what is the estimated incidence of intraoperative awareness under general anaesthesia?
  5. [AS4.4] How do you manage intraoperative hypotension in an anaesthetised patient? Describe a systematic approach using the DR ABC mnemonic (Depth reduction, Restore volume, Address arrhythmia, Blood-vessel tone, Cardiac contractility). When would you escalate to vasopressors?