Anaphylaxis
Formal Definition
A severe, potentially life-threatening allergic reaction involving multiple organ systems; characterized by rapid onset (minutes to hours) after exposure to an allergen; involves IgE-mediated mast cell and basophil degranulation causing urticaria, angioedema, bronchospasm, and cardiovascular collapse; requires immediate intramuscular epinephrine as first-line treatment.
How It's Used on the Ward
Anaphylaxis or having an allergic reaction or patient is anaphylactic — a severe systemic allergic reaction that can kill in minutes if not treated.
Example
"Patient eaten shrimp 10 minutes ago: perioral swelling, urticaria on trunk, wheeze, BP 75/40, HR 130. Diagnosis: anaphylaxis. IM epinephrine 0.5 mg (1:1000) into lateral thigh immediately. Patient laid supine, legs elevated. Calling for backup. Second dose in 5 minutes if no improvement. Starting oxygen, preparing for intubation if airway worsens."
Clinical Context
Diagnostic criteria (NIAID/FAAN): involvement of skin/mucosal (urticaria, angioedema) PLUS either respiratory compromise (stridor, wheeze, dyspnea) OR hypotension/end-organ dysfunction → anaphylaxis. Skin findings absent in 10-20% of anaphylaxis — do not wait for rash if other signs present. Epinephrine: 0.3-0.5 mg IM (1:1000) in lateral thigh, repeat q5-15min PRN. IV epinephrine only for refractory hypotension in monitored setting. Adjuncts: antihistamines (diphenhydramine), H2 blocker (famotidine), bronchodilators (albuterol), corticosteroids (delayed benefit). Biphasic reaction: 20% of patients have second reaction hours later — observe for 4-8h, longer if severe.