Overview
Definition
A severe, potentially life-threatening, systemic hypersensitivity reaction.
Epidemiology
Lifetime prevalence of 1-2%. Common triggers include foods (peanuts, shellfish), insect stings, and medications (Penicillin).
Etiology & Risk Factors
- Type I Hypersensitivity reaction: Allergen cross-links IgE on the surface of mast cells and basophils.
- Massive, sudden degranulation releases histamine, leukotrienes, and prostaglandins, causing systemic vasodilation and increased capillary permeability.
Clinical Symptoms
- Dermatologic: Hives (urticaria), pruritus, flushing, angioedema (swelling of lips, tongue, face)
- Respiratory: Wheezing, stridor, shortness of breath, throat tightness
- Cardiovascular: Tachycardia, severe hypotension, shock
- Gastrointestinal: Nausea, vomiting, crampy abdominal pain
Clinical Approach
Diagnosis
- Clinical diagnosis. Requires acute onset (minutes to hours) with involvement of the skin/mucosa PLUS either respiratory compromise or hypotension.
Management
- Epinephrine (IM into the anterolateral thigh): THE FIRST AND MOST IMPORTANT TREATMENT. Stimulates alpha-1 (vasoconstriction) and beta-2 (bronchodilation) receptors.
- IV Fluids: Aggressive resuscitation for hypotension
- Adjuncts: Antihistamines (H1/H2 blockers like Diphenhydramine/Famotidine) and Corticosteroids (Methylprednisolone) to prevent a biphasic reaction (recurrence of symptoms hours later). These DO NOT save lives in the acute phase; only Epinephrine does.
- Albuterol nebulizers for bronchospasm
Complications
- Anaphylactic Shock (cardiovascular collapse)
- Asphyxiation (due to severe laryngeal edema)