Perioperative Anaphylaxis: An EDAIC Viva Differential
Reason through sudden hypotension and bronchospasm in an original perioperative viva, including absent skin signs, competing causes and follow-up.
Perioperative anaphylaxis can present with cardiovascular collapse, bronchospasm or both, without an obvious rash. In an EDAIC viva, the task is to recognise a dangerous pattern, act on it and test competing explanations in parallel. It is not to wait for every feature of a textbook description.
The NAP6 clinical-features report documents why absent skin signs cannot exclude severe perioperative anaphylaxis. This article uses an original scenario to practise reasoning; emergency treatment should follow the applicable perioperative anaphylaxis algorithm.
The opening scenario
An adult is anaesthetised for elective surgery. Shortly after several perioperative exposures, arterial pressure falls markedly, airway pressure rises and the capnography trace becomes smaller. No skin changes are visible on the uncovered areas. The examiner asks: “What concerns you?”
A strong first answer is short: “This is acute cardiorespiratory deterioration. Anaphylaxis is a leading possibility, but I would immediately assess airway, breathing, circulation and the equipment while calling for help and treating the instability.”
That answer does three useful things. It names severity, offers a working diagnosis and avoids premature certainty. An exhaustive list of rare causes before acknowledging the emergency would be a weaker response.
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Arrange the differential by what would discriminate
| Possible explanation | Information that would help distinguish it |
|---|---|
| Anaphylaxis | Exposure chronology and multisystem deterioration; skin signs may be absent |
| Airway or circuit problem | Tube position, patency, circuit examination and ventilation findings |
| Haemorrhage or major loss of circulating volume | Surgical field, losses and haemodynamic context |
| A mechanical intrathoracic problem | Examination, ventilation changes, procedural circumstances and targeted imaging when appropriate |
| Predominant drug-related cardiovascular depression | Drugs, timing, dose context and absence or presence of other explanatory features |
The table is a way to organise an exam answer, not a rule that one finding proves a diagnosis. For example, high airway pressure has several causes. The useful question is whether there is a coherent explanation for the simultaneous pressure, ventilation and circulation changes.
If the examiner adds that hand ventilation is difficult, that observation increases the importance of the airway and respiratory assessment. It does not remove anaphylaxis from consideration. If major surgical bleeding is then revealed, the differential changes again. Reassessing is a strength when new evidence arrives.
Do not confuse timing with proof of a culprit
The phrase “after the antibiotic” is clinically important, but chronology alone is not a completed allergy investigation. Several agents and materials may have been encountered around the same period, and some exposures are easier to overlook than a recorded intravenous bolus.
For the viva, separate three statements:
- A reaction is suspected and must be managed now.
- An exposure is temporally associated and should be documented.
- A specific culprit and safe alternatives require appropriate specialist investigation.
The distinction prevents an emergency working diagnosis from becoming an unjustified permanent label. A detailed timeline is more useful than retrospectively declaring one agent responsible because it was the most memorable event.
Answer an EDAIC-style question
This is one exam-format Part 1 multiple-true-false question from our bank. Mark each statement true or false, then see the worked answer.
Regarding the pathophysiology of oxygen delivery and consumption in circulatory shock:
Mark each statement true or false:
In healthy adults at rest, systemic oxygen delivery is approximately 1000 mL/min while oxygen consumption is about 250 mL/min, creating a physiological oxygen reserve.
When systemic oxygen delivery decreases, oxygen consumption immediately falls in direct proportion, indicating supply dependency at all levels of DO₂.
Cardiac output is determined by the product of heart rate and stroke volume, with stroke volume being influenced by preload, afterload, and myocardial contractility.
The unifying feature of all forms of shock, regardless of aetiology, is acute circulatory failure associated with inadequate cellular oxygen utilisation.
In septic shock, early goal-directed therapy targeting supranormal oxygen delivery values has been shown to consistently reduce mortality across all patient populations.
The treatment explanation should remain coherent
Anaphylaxis creates problems with vascular tone, vascular permeability and, in some cases, the airway and breathing. That is why its management cannot be explained as merely “give an antihistamine”. The RCUK resources provide separate perioperative guidance for clinicians managing this setting.
In an exam answer, state that resuscitation and the appropriate adrenaline-based algorithm take priority, alongside removing a suspected ongoing trigger where possible. Do not delay urgent treatment for blood tests. Exact routes, doses and escalation belong to the current clinical algorithm and the treating team's setting; they are not reproduced as a dosing recipe here.
An examiner may ask why the response to treatment is also informative. The useful answer is that repeated observations help assess improvement and reveal an alternative or additional cause. A temporary improvement should not end the assessment if instability returns.
After the crisis: what should the candidate remember?
The 2024 perioperative guidance describes appropriately timed acute and baseline tryptase sampling, clear documentation and subsequent investigation. A sample is evidence to interpret in context; it is not a reason to postpone resuscitation or a standalone identification of the responsible allergen.
For an original practice task, write a six-line handover using only information supplied by the scenario: onset time, exposure timeline, observed features, interventions, response and investigation/follow-up plan. Leave missing facts marked as missing. This is better practice than inventing a persuasive but unsupported sequence.
The SOE answer framework can help you keep urgent priorities ahead of detailed explanations. Compare the differential with local anaesthetic systemic toxicity, while remembering that similar instability does not make the underlying mechanisms identical.
Three examiner follow-ups
“There is no rash. Does that reassure you?” Not sufficiently. The absence of visible skin signs cannot rule out severe perioperative anaphylaxis, and drapes may limit observation.
“Should you obtain tryptase before treating?” No. Sampling must not delay resuscitation. Explain when and why samples will be taken once immediate care permits.
“Can you document a confirmed allergy to the last drug given?” You can document a suspected reaction and accurate chronology. Confirmation and future drug recommendations require the appropriate investigation.
Use AnesCORE practice to connect recognition with mechanism, then rehearse the opening answer aloud without looking at the differential table.
Sources
- RCUK and Perioperative Allergy Network: 2024 perioperative anaphylaxis algorithm
- Royal College of Anaesthetists: NAP6 clinical features
- Resuscitation Council UK: current anaphylaxis guidance resources
Prepared with AI assistance for examination revision; sources checked 6 November 2026. These original teaching examples are not official EDAIC questions. Not a patient-care protocol.
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