Acute management of anaphylaxis

This is anaphylaxis: the rapid onset after a known allergen of airway, respiratory and circulatory compromise with skin changes. The diagnosis is clinical and the treatment begins immediately.^[1]

Call for help and assess the airway, breathing and circulation. The first and decisive treatment is intramuscular adrenaline, 500 micrograms of 1-in-1000, into the anterolateral aspect of the middle of the thigh, repeated every five minutes if there is no response.^[2] Position the patient lying flat with the legs elevated to maximise venous return (sitting up if breathless), give high-flow oxygen, and establish intravenous access for a rapid crystalloid bolus — the capillary leak can cause profound volume depletion. Remove the sting if it is still present.

Reassess continuously and repeat the adrenaline; a second dose is needed in a substantial minority. Once stable, add the adjuncts: a nebulised bronchodilator for the wheeze, an H1 antihistamine (with or without an H2 blocker) and hydrocortisone — these relieve the skin and may modulate the late reaction, but they are not first-line. Take a mast-cell tryptase (now and at one to two hours) to confirm the diagnosis retrospectively. Observe the patient for the biphasic reaction, particularly given the hypotension, and on recovery discharge with two adrenaline auto-injectors, a written action plan, and an allergy clinic referral.^[1]

If he does not respond to two doses of intramuscular adrenaline, the escalation is an intravenous adrenaline infusion, titrated by an experienced clinician; if he is on a beta-blocker, give glucagon.^[1]