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AS4.3-5 | Induction, Maintenance, Monitoring and Vital Organ Support During Anaesthesia — SDL Guide (Part 3)
Self-Assessment: Procedural Reasoning in General Anaesthesia
To confirm your understanding of the conduct of general anaesthesia at the level expected for AS4.3–AS4.5, work through the following clinical reasoning exercises before your operating theatre observation sessions.
Case 1: You are observing a general anaesthetic for an appendicectomy in a 22-year-old previously healthy male. Fasting status: last ate 7 hours ago. At induction (propofol 160 mg), the patient's blood pressure drops from 125/80 to 78/48 mmHg. Heart rate increases from 72 to 108/min. Identify the likely cause. What is the immediate management sequence? At what BP would you consider intervening and what drug would you use first — ephedrine or phenylephrine? Justify your choice based on the haemodynamic physiology.
Case 2: Thirty minutes into a laparotomy under balanced anaesthesia (sevoflurane 2%, fentanyl infusion, rocuronium), the SpO₂ falls from 99% to 89% and ETCO₂ rises from 38 to 55 mmHg. Breath sounds are absent on the right. List your differential diagnoses in order of probability, and for each, state what examination finding or monitoring change would confirm it. What is the most immediately reversible cause and how do you treat it?
Case 3: At the end of a 3-hour abdominal surgery, you give neostigmine 2.5 mg with glycopyrrolate 0.5 mg. Five minutes later, the TOF ratio is 0.74. The surgeon wants to start closing. What does TOF 0.74 mean clinically? Is it safe to extubate? What do you do next?
For each case, write out your clinical reasoning — not just the answer, but the physiological mechanism behind your decision. This is the level of understanding that AS4.3–AS4.5 require you to demonstrate in your portfolio and clinical assessments.
CLINICAL PEARL
Capnography is the stethoscope of anaesthesia. In the modern operating theatre, the end-tidal CO₂ waveform (capnograph) provides more continuous, quantitative information about ventilation, circulation, and metabolism than any other single monitor. A flat capnograph trace immediately after intubation means oesophageal intubation until proven otherwise — the SpO₂ will not drop immediately (pre-loaded oxygen in FRC buys time) but CO₂ will not appear. A suddenly flat trace during maintenance means cardiac arrest or massive PE. A steadily rising EtCO₂ with a 'shark fin' waveform is bronchospasm or COPD with air-trapping. A rapidly rising EtCO₂ with rising temperature is malignant hyperthermia. Learn to read capnography — one trace, many diagnoses.