Anaphylaxis
Anaphylaxis is a sudden, potentially life‑threatening systemic hypersensitivity reaction causing rapid onset of airway, breathing and/or circulatory compromise. Immediate recognition and prompt treatment - principally intramuscular (IM) adrenaline into the anterolateral mid‑thigh - are essential (RCUK; NICE).
Pathophysiology
- IgE‑mediated (Type I): allergen exposure leads antigen‑specific B cells to produce IgE, which binds FcεRI on mast cells and basophils. Re‑exposure causes IgE cross‑linking, mast‑cell/basophil degranulation and release of histamine, tryptase and other mediators, producing vasodilatation, increased vascular permeability and smooth‑muscle contraction.
- Non‑IgE mechanisms: direct mast‑cell activation or complement activation can produce the same clinical phenotype. Management is identical to IgE‑mediated anaphylaxis.
Common triggers
- Foods (most common in children): nuts, shellfish, milk, eggs.
- Drugs: β‑lactam antibiotics (penicillins), NSAIDs/aspirin, neuromuscular blockers, radiological contrast media and others.
- Venom: wasp and bee stings.
- Latex.
- Idiopathic reactions.
- Exposures with possible prolonged absorption (for example, slow‑release medications or depot formulations).
Recognition - key clinical features Suspect anaphylaxis with sudden onset and rapid progression of illness involving one or more of the following systems:
- Airway: angioedema (tongue, face, upper airway), hoarseness, stridor.