Deaths from anaphylaxis are associated with delayed adrenaline, and the delay usually comes from three habits: reaching for an antihistamine or steroid first, using the subcutaneous or intravenous route, and waiting for hypotension before accepting the diagnosis.
Adrenaline 0.5 mg of 1 mg/mL intramuscularly into the anterolateral thigh, repeated at five minutes if there is no improvement, is the treatment. Antihistamines do nothing for airway or circulation and steroids do not prevent biphasic reactions on current evidence — give them afterwards if at all. Two features are enough to act on: sudden onset with skin or mucosal change plus either respiratory compromise or hypotension, and in a patient with a known allergen, respiratory or cardiovascular compromise alone will do.
Three points catch people out. Lie the patient flat with legs raised and do not sit them up — standing has been associated with sudden cardiac arrest in this setting. Patients on beta-blockers may respond poorly and need glucagon. And a patient who needed more than one dose, or who has asthma, warrants longer observation before discharge, with an adrenaline autoinjector and a written plan if one is available.
- Intramuscular adrenaline into the anterolateral thigh, first, before any other drug
- Repeat at five minutes if there is no improvement — under-dosing by omission is the usual error
- Keep the patient lying flat with legs raised; do not sit them upright
- Consider glucagon in patients on beta-blockers who do not respond
- Observe longer after a second dose or in asthma, and discharge with a plan and an autoinjector where available
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