General Anaesthesia and Airway Management
This domain tests how you assess, secure and maintain the airway, and how you conduct a general anaesthetic from preoxygenation through to safe emergence. Questions usually arrive as a scenario stem - a predicted difficult airway, an aspiration risk, or a sudden desaturation after induction - and reward a structured, algorithmic answer rather than a list of drugs.
Preoxygenation and rapid sequence induction
- Three minutes of tidal-volume breathing through a tight-fitting mask, or eight vital-capacity breaths, achieves end-tidal O2 above 0.9 and gives roughly 8 minutes of safe apnoea in a healthy adult; obesity, pregnancy and small children reduce this to 2–3 minutes.
- Nasal apnoeic oxygenation at 15 L/min extends the safe apnoeic period and should be routine whenever difficulty is predicted.
- RSI means a pre-calculated hypnotic plus rocuronium 1.2 mg/kg (intubating conditions in about 60 seconds) or suxamethonium 1.5 mg/kg; sugammadex 16 mg/kg is the rescue after a failed RSI with rocuronium.
Assessment and the failed airway
Predictors include Mallampati III–IV, thyromental distance under 6.5 cm, mouth opening under 3 cm, reduced cervical mobility and previous difficulty. Work through the DAS-style sequence: Plan A laryngoscopy (video laryngoscope first in predicted difficulty), Plan B supraglottic airway, Plan C face-mask ventilation, Plan D front-of-neck access with scalpel and bougie. Continuous waveform capnography - not auscultation - confirms tracheal placement.
Worked example
A 45-year-old woman, BMI 38, diabetic, Mallampati IV, needs emergency laparotomy. You sit her up 25 degrees, preoxygenate to end-tidal O2 above 0.9 with nasal oxygen running, give ketamine 1.5 mg/kg and rocuronium 1.2 mg/kg, and intubate with video laryngoscopy at the first attempt. If that fails you insert a second-generation supraglottic airway; if oxygenation still fails you proceed to scalpel–bougie cricothyroidotomy without further attempts at laryngoscopy.
Traps
Oesophageal intubation recognised late because capnography was not applied from the moment of intubation; failing to reduce the induction dose in shock; giving suxamethonium in hyperkalaemia, burns beyond 24 hours or prolonged immobility; and describing a difficult airway plan that stops at Plan B with no Plan D stated.