Anaphylaxis: recognition and emergency management — formative SAQs

SAQ 1 (10 marks)

A four-year-old boy with a known peanut allergy develops, ten minutes after eating a biscuit at a party, sudden flushing, lip and tongue swelling, drooling and a wheeze. His mother gives his adrenaline autoinjector into his thigh and calls an ambulance. On arrival he is improving but still has urticaria and mild wheeze. [1]

Question: Outline the immediate and stepwise emergency management of this child, the observation decision, and the discharge package. (10 marks) [3]

Model answer

Recognition and first response (2 marks). This is anaphylaxis under the NIAID/FAAN criteria — acute skin and mucosal involvement (flushing, lip and tongue swelling, urticaria) plus respiratory compromise (drooling suggesting upper-airway oedema, and wheeze). The mother's early adrenaline was exactly right. On arrival, confirm the ABCDE status, continue to lie him flat with legs raised (sit up only if breathing distressed), remove any remaining trigger, and call for the resuscitation team. Up to a fifth of reactions have no skin signs, so the presence of skin signs here makes the diagnosis clear but should never be the reason to delay adrenaline in another child. [1]

Adrenaline — first-line, intramuscular (2 marks). Adrenaline is the decisive drug, given intramuscularly into the anterolateral thigh where absorption is fastest and most reliable. For a four-year-old (under about six years and under thirty kilograms) the dose is 150 micrograms — 0.15 millilitres of the 1 milligram per millilitre concentration, equivalent to the junior autoinjector the mother used. The dose is repeated every five minutes if there is no response. Adrenaline works through its receptor profile: alpha-1 reverses the oedema and the distributive shock, beta-2 bronchodilates and stabilises the mast cell, beta-1 supports the circulation. [3]

Adjuncts (2 marks). Give high-flow oxygen for hypoxia or an oxygen saturation below 94 per cent. Give an intravenous crystalloid bolus of 10 millilitres per kilogram if there is hypotension or poor perfusion, repeating to 20 millilitres per kilogram if needed, because the vasodilation and capillary leak create large fluid deficits. Nebulised salbutamol treats refractory wheeze. An H1 antihistamine relieves urticaria and pruritus; a corticosteroid and an H2 blocker are traditional adjuncts. None of these replaces adrenaline or should delay it — they are for symptom comfort and the historical hope of preventing a biphasic reaction. [3] [4]

Observation and the biphasic reaction (2 marks). Because symptoms can recur one to seventy-two hours after the initial resolution without further allergen exposure — the biphasic reaction — the child cannot simply be sent home. This presentation resolved after a single adrenaline dose with full recovery, so a minimum of around six hours' observation is reasonable, provided the family has good access to emergency care. If the child had needed two or more adrenaline doses, had a refractory or severe course, has asthma, is on a beta-blocker, or has poor access to care, admit overnight. The paediatric repeat-epinephrine cohort evidence supports this severity-graded approach rather than a single blanket duration. [9] [10]

Discharge package (2 marks). Before discharge the child must leave with the prevention package: an adrenaline autoinjector (ideally two), prescribed with a device-matched trainer; a written ASCIA action plan naming the trigger, the dose and the steps, copied to the school or childcare; a referral to the allergy clinic to confirm the trigger with skin-prick and specific-IgE testing and, where indicated, a supervised oral food challenge; and family and school education on strict peanut avoidance, when and how to use the autoinjector, and to call an ambulance immediately and use a second device if there is no response. Sending the child home without this package sets up a recurrent, potentially fatal reaction. [8] [3]

SAQ 2 (10 marks)

Question: A 15-year-old girl with asthma and a peanut allergy becomes dizzy, wheezy and pale in the school yard after shared food. She has no rash. (a) What is the diagnosis and why is the absence of a rash not reassuring? (b) Outline the immediate management and the escalation if she does not respond to two adrenaline doses. (c) Explain the tryptase timing and interpretation. (10 marks) [1]

Model answer

(a) Diagnosis and the no-rash pitfall (3 marks). The diagnosis is anaphylaxis. The acute respiratory compromise (wheeze, dizziness) and the distributive-shock picture (pallor, presyncope) after a likely food allergen in a known peanut-allergic child meet the NIAID/FAAN criteria even without skin signs — two or more systems after a likely allergen. The absence of a rash is not reassuring because up to a fifth of anaphylactic reactions have no skin signs at all, and this is precisely the presentation at highest risk of fatal outcome: the asthmatic adolescent with food anaphylaxis and delayed adrenaline. Waiting for a rash before giving adrenaline is a recognised and avoidable contributor to fatal cases. [1]

(b) Immediate management and refractory escalation (5 marks). Call for help and an ambulance, lie her flat with legs raised (sit up only if breathing distressed, left lateral if she loses consciousness), and give intramuscular adrenaline into the anterolateral thigh immediately. At fifteen years and over fifty kilograms the dose is 500 micrograms — 0.5 millilitres of the 1 milligram per millilitre concentration, repeated every five minutes if there is no response. Give high-flow oxygen for hypoxia, an intravenous crystalloid bolus of 10 millilitres per kilogram for hypotension, and a nebulised bronchodilator for the wheeze; treat her asthma concurrently because the bronchospasm compounds an already reactive airway. [3]

If she does not respond to two intramuscular adrenaline doses and adequate fluid — refractory anaphylaxis — escalate to an intravenous adrenaline infusion starting at 0.1 to 1 microgram per kilogram per minute, titrated to the response, managed in the paediatric intensive care unit with senior support. Check the medication list for a beta-blocker: if she is on one and refractory to adrenaline, give glucagon, which bypasses the receptor blockade. Reserve an intravenous bolus of about 1 microgram per kilogram for the peri-arrest or arrested patient under experienced hands. [4]

(c) Tryptase timing and interpretation (2 marks). Draw serum tryptase as soon as possible after onset, again at one to two hours, and at a baseline point at least twenty-four hours later; a rise exceeding 1.2 times the baseline plus 2 micrograms per litre confirms mast-cell activation. The critical point for the examiner is that a normal tryptase never excludes anaphylaxis — food-triggered reactions are often tryptase-normal — so treatment must never be delayed or denied on the result. Tryptase is a confirmatory tool, not a decision rule for adrenaline. [4]