Define Anaphylaxis. Describe its clinical features, management and pathophysiology.

Definition

Anaphylaxis is a severe, potentially fatal, systemic hypersensitivity reaction (usually IgE-mediated) with rapid onset after exposure to an allergen (foods, drugs, insect stings, latex).

Clinical Features

• Skin/mucosa — urticaria, flushing, angioedema (lips/face).
• Respiratory — stridor, bronchospasm/wheeze, respiratory distress.
• Cardiovascular — hypotension/shock, tachycardia.
• Gastrointestinal — vomiting, abdominal pain; rapid progression is typical.

Management

• Intramuscular adrenaline is the first-line, life-saving treatment — give immediately.
• Remove the trigger; position (supine, legs up; upright if breathing difficulty); high-flow oxygen.
• IV fluids for hypotension; bronchodilators for wheeze.
• Adjuncts (antihistamine, corticosteroid) are secondary; observe for a biphasic reaction.
• Provide an adrenaline auto-injector and allergen-avoidance advice on discharge.

Common Triggers & Biphasic Risk

• Foods (nuts, egg, milk, seafood), drugs (antibiotics, NSAIDs), insect stings and latex.
• A biphasic reaction (recurrence hours later) means patients must be observed after initial recovery.

Pathophysiology

Mast-cell/basophil degranulation releases histamine and other mediators, causing vasodilatation (hypotension), increased vascular permeability (angioedema), and bronchoconstriction — which adrenaline directly reverses.

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