Anaphylactic shock

Anaphylactic shock is life-threatening circulatory failure caused by a severe systemic allergic reaction. Widespread blood-vessel dilation and fluid leakage can sharply reduce blood pressure and impair organ perfusion.

Anaphylaxis: A severe, rapid systemic hypersensitivity reaction that can affect the skin, airways, circulation, or digestive system. Anaphylactic shock is the circulatory-collapse form of this broader reaction.
Epinephrine: A hormone and medication that stimulates alpha- and beta-adrenergic receptors. Intramuscular epinephrine is first-line treatment because it supports blood pressure and opens narrowed airways.
Type I hypersensitivity: An immediate immune reaction in which allergen-specific IgE activates mast cells and basophils. This is the classic immune pathway behind many cases of anaphylactic shock.
Vasovagal syncope: A brief loss of consciousness caused by a reflex drop in heart rate or blood pressure. It can follow injections or distress, but usually lacks the multisystem allergic features of anaphylaxis.
Anaphylaxis diagnostic criteria: Clinical criteria used to identify anaphylaxis from symptom patterns and likely exposure. Shock may be diagnosed from sudden hypotension after a likely trigger, even without skin symptoms.
Mast cell: A tissue-resident immune cell that releases histamine and other mediators during allergic reactions. Mast-cell activation releases mediators that drive vasodilation and vascular leakage.
Intramuscular injection: Delivery of a medication into muscle tissue for absorption into the bloodstream. The outer thigh is the recommended site for initial epinephrine treatment.
Immunoglobulin E: An antibody class involved in allergic responses and defense against some parasites. Allergen-bound IgE can trigger the cell activation that releases allergic mediators.
Septic shock: Life-threatening circulatory and cellular dysfunction caused by a dysregulated response to infection. Both may involve vasodilation and low blood pressure, but infection drives septic shock.
Serum tryptase: A blood measurement of tryptase, an enzyme released mainly by activated mast cells. A timed sample can support diagnosis, but a normal result does not exclude anaphylaxis.

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