This is the anaesthetic emergency most likely to appear as a clinical judgement scenario, and it rewards decisiveness. The panel is not testing whether you can recite a drug chart — it is testing whether you recognise it early, act without waiting for certainty, and know when to get help.

Why is it harder to spot under anaesthesia?

Every early warning you would normally rely on is unavailable. The patient cannot tell you they feel unwell, the skin is under drapes, and hypotension has a dozen benign explanations in theatre. Say that out loud — it shows you understand the setting rather than the textbook.

  • Cardiovascular collapse is the commonest presenting feature, and often the only one
  • Bronchospasm, or rising airway pressures that will not settle
  • A rash you cannot see until the drapes come down
  • Timing matters: it usually follows induction, and the trigger is usually something given in the last few minutes

What do you do first?

Call for help and stop the likely trigger, then give adrenaline. Do not wait for a diagnosis to be certain — delay is what harms these patients.

  • Stop the probable trigger and stop surgery if you can
  • 100% oxygen, and secure the airway if it is not already
  • Adrenaline — an initial intravenous bolus of 50 micrograms, repeated and escalated by response; 100 micrograms may be chosen where cardiovascular disturbance is severe
  • Large-volume IV fluid: these patients are profoundly vasodilated and need far more than feels reasonable
  • Consider an adrenaline infusion early if repeated boluses are needed

The intravenous dose is the one candidates get wrong, because they carry over the 500 microgram intramuscular dose from community anaphylaxis. In theatre, with a cannula, monitoring and an anaesthetist present, it is 50 micrograms IV.

What investigations, and when?

Mast cell tryptase, timed. Take a sample as soon as the patient is stable, a second at one to two hours, and a third after 24 hours as a baseline. The timing is the point — a single sample proves little.

What happens afterwards?

Every patient is referred to a specialist perioperative allergy clinic for testing, and told clearly what happened. Documentation and a critical incident report follow. Being able to say that the episode does not end when the patient stabilises is what marks a reflective answer.

NAP6 examined every case of life-threatening perioperative anaphylaxis across UK NHS hospitals over a year, against roughly three million anaesthetics. Knowing that it exists, and that it is why UK practice looks as it does, is worth a sentence.