EM · Anaphylaxis
Anaphylaxis (the emergency of the IM adrenaline)
Also known as Anaphylactic shock · Allergic emergency · Severe allergic reaction
Anaphylaxis — the rapid, severe, multi-system allergic reaction; the IgE-mediated mast cell degranulation; the clinical diagnostic criteria (the sudden onset with the skin or the mucosal change and the respiratory and/or the cardiovascular involvement); the triggers (the food, the venom, the drug, the contrast, the latex, the exercise); the emergency management (the intramuscular adrenaline 500 micrograms into the anterolateral thigh, repeated every 5 minutes; the high-flow oxygen; the intravenous fluid; the chlorphenamine; the hydrocortisone; the observation for the biphasic reaction); the refractory anaphylaxis (the intravenous adrenaline infusion); and the beta-blocker patient (the glucagon). ACEM-primary, globally tagged.
Checked against its sources on 2 Sept 2026
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Red flags
- The first-line treatment is the intramuscular adrenaline 500 micrograms into the anterolateral thigh — NOT the intravenous, NOT the subcutaneous, and NOT the oxygen first
- The adrenaline is repeated every 5 minutes if the response is inadequate — the under-dosing and the delayed dosing are the recurring fatal errors
- A beta-blocker patient with an anaphylaxis may not respond to the adrenaline — give the glucagon 1 to 5 mg intravenously
- The biphasic reaction occurs in about 5 per cent of patients (median onset 11 hours, range up to 72 hours) — the observation for 6 to 12 hours is the standard
- A layperson's EpiPen delivers 300 micrograms; the emergency department gives 500 micrograms from the ampoule — do not rely on the auto-injector in the ED
Anaphylaxis is the prototype of the time-critical emergency that every emergency physician must manage automatically — the IM adrenaline dose and the route must be as reflexive as the defibrillation for the VF, because the under-dosing, the delayed dosing and the wrong route are the recurring fatal errors. The Fellowship candidate must know the diagnostic criteria, the immediate algorithm with the doses, the refractory-anaphylaxis escalation, and the beta-blocker trap, because these are the decisions that separate the candidate who saves from the one who loses the preventable death.[1][2]
Definition and the mechanism
Anaphylaxis is a rapid, severe, life-threatening systemic hypersensitivity reaction. It is most commonly IgE-mediated — the allergen cross-links the IgE on the mast cells and the basophils, triggering the explosive degranulation and the release of the histamine, tryptase, leukotrienes, prostaglandins and the platelet-activating factor. These mediators produce the vasodilation (the shock), the bronchoconstriction (the wheeze), the increased vascular permeability (the angioedema, the urticaria) and the mucus secretion (the upper-airway obstruction). The non-IgE-mediated (the anaphylactoid) reactions — from the radiocontrast, the NSAID, the opiate, the exercise and the idiopathic — share the same clinical presentation and the same management. [1]
References10ShowHide
- [1]Nasr I, Mahdi AS, Al Shekaili J, et al. Real World Management of Anaphylaxis Versus the National Institute for Health and Clinical Excellence (NICE) Guidelines Cureus, 2022.PMID 36277549
- [2]Srivastava S, Huissoon AP, Barrett V, et al. Systemic reactions and anaphylaxis with an acute serum tryptase ≥14 μg/L: retrospective characterisation of aetiology, severity and adherence to National Institute of Health and Care Excellence (NICE) guidelines for serial tryptase measurements and specialist referral J Clin Pathol, 2014.PMID 24782357
- [3]Wood RA, Camargo CA Jr, Lieberman P, et al. Anaphylaxis in America: the prevalence and characteristics of anaphylaxis in the United States J Allergy Clin Immunol, 2014.PMID 24144575
- [4]Turner PJ, Campbell DE, Motosue MS, et al. Global Trends in Anaphylaxis Epidemiology and Clinical Implications J Allergy Clin Immunol Pract, 2020.PMID 31786255
- [5]Simons FE, Gu X, Simons KJ Epinephrine absorption in adults: intramuscular versus subcutaneous injection J Allergy Clin Immunol, 2001.PMID 11692118
- [6]Lee S, Bellolio MF, Hess EP, et al. Time of onset and predictors of biphasic anaphylactic reactions: a systematic review and meta-analysis of 27 studies J Allergy Clin Immunol Pract, 2015.PMID 25680923
- [7]Kim TH, Yoon SH, Hong H, et al. Duration of Observation for Detecting a Biphasic Reaction in Anaphylaxis: A Meta-analysis Int Arch Allergy Immunol, 2019.PMID 30763927
- [8]Harper NJN, Cook TM, Garcez T, et al. Anaesthesia, surgery, and life-threatening allergic reactions: management and outcomes from the Sixth National Audit Project Br J Anaesth, 2018.PMID 29935569
- [9]Umasunthar T, Leonardi-Bee J, Hodes M, et al. Incidence of fatal food anaphylaxis in people with food allergy: a systematic review and meta-analysis Clin Exp Allergy, 2013.PMID 24118190
- [10]Cardona V, Ansotegui IJ, Ebisawa M, et al. World allergy organization anaphylaxis guidance 2020. World Allergy Organ J, 2020.PMID 33204386