anaphylactic shock
Summary
Anaphylactic shock is a severe, life-threatening systemic allergic reaction characterized by rapid onset of cardiovascular collapse, respiratory distress, and multi-organ dysfunction. It results from massive mast cell and basophil degranulation releasing inflammatory mediators, particularly histamine and leukotrienes, leading to vasodilation, increased vascular permeability, and bronchoconstriction.
Detail
Anaphylactic shock is a Type I (IgE-mediated) hypersensitivity reaction that occurs within minutes of exposure to an allergen in previously sensitized individuals. The pathophysiology involves cross-linking of allergen-specific IgE antibodies bound to mast cells and basophils, triggering massive degranulation and release of preformed mediators (histamine, tryptase, heparin) and newly synthesized mediators (leukotrienes, prostaglandins, platelet-activating factor). This leads to profound vasodilation and increased capillary permeability causing distributive shock, severe bronchoconstriction causing respiratory failure, and potential cardiovascular collapse. Clinical manifestations include urticaria, angioedema, bronchospasm, laryngeal edema, hypotension, tachycardia, and GI symptoms. Common triggers include foods (peanuts, shellfish), medications (penicillin, NSAIDs), insect stings, and latex. Diagnosis is clinical, supported by elevated serum tryptase levels. Treatment requires immediate epinephrine administration, IV fluids, corticosteroids, and H1/H2 antihistamines. Without prompt treatment, anaphylactic shock can be fatal within minutes due to respiratory failure or cardiovascular collapse.
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
- Harrison's Principles of Internal Medicine
- Janeway's Immunobiology
- UpToDate: Anaphylaxis
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