Anaphylaxis
A rapidly developing systemic hypersensitivity reaction in which mast-cell mediator release obstructs the airway, closes the small airways and empties the circulation, reversed by intramuscular adrenaline given within minutes.
Definition
A severe, usually rapid-onset systemic hypersensitivity reaction that can kill through life-threatening compromise of the airway, breathing or circulation. Typical skin features and frank circulatory shock may both be absent.
First principles
Anaphylaxis is life-threatening airway, breathing or circulation compromise, not a rash
Anaphylaxis is likely when someone exposed to a trigger develops sudden illness with rapidly progressing airway, breathing or circulation problems. Skin or mucosal changes usually accompany it, but are subtle or absent in 10 to 20% of reactions. Skin changes on their own are not anaphylaxis. Waiting for urticaria before giving adrenaline is a diagnostic error, not caution.
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.