Pathophysiology
Clinical meaning
Anaphylactic shock is a severe, life-threatening type I hypersensitivity reaction mediated by IgE antibodies. Upon re-exposure to an allergen, IgE bound to mast cells and basophils triggers massive degranulation releasing histamine, leukotrienes, prostaglandins, and other mediators. Histamine causes rapid vasodilation, increased vascular permeability, bronchospasm, and increased mucus production. Massive vasodilation and third-spacing of fluid cause distributive shock with profound hypotension. Laryngeal edema can cause complete airway obstruction within minutes. The biphasic response occurs in 5-20% of cases where symptoms recur 4-12 hours after initial resolution without re-exposure. Common triggers include medications (penicillin, NSAIDs), foods (peanuts, shellfish, tree nuts), insect stings (bee, wasp), latex, and contrast media. Epinephrine is the ONLY first-line treatment and must not be delayed.