PULMONARYQ
ANAPHYLAXIS
Definition and pathophysiology (Ann Emerg Med 2006;47:373)
• Severe, rapid-onset (mins to hrs), potentially life-threatening systemic allergic response
• IgE-mediated mast cell degranulation with release of histamine, tryptase and TNF
• Precipitates systemic reactions (bronchospasm, tissue swelling, fluid shifts, vasodilation)
• Common triggers: penicillins, cephalosporins, shellfish, nuts, insect stings, IV contrast (not truly an IgE-mediated mechanism, but clinically similar)
Diagnosis: any of the three following criteria
1) Acute illness with skin ± mucosal involvement (rash, flushing, hives), AND at least one of:
• Respiratory compromise (wheeze, stridor, dyspnea, hypoxemia)
• Hypotension or hypoperfusion (syncope, incontinence)
2) Two or more of the following after exposure to a likely allergen: skin/mucosal involvement, respiratory compromise, ↓ BP or hypoperfusion, GI symptoms
3) Hypotension after exposure to known allergen for that Pt
Treatment
• Epinephrine: IM or SC 0.3–0.5 mL of 1:1000 dilution (1 mg/mL) q5–20min; if HoTN or cardiac arrest, IV (or via ETT) 2.5–10 mL of 1:10,000 dilution q5min ± gtt
• Airway management: suppl O2 ± intubation (or cricothyroidotomy if laryngeal edema) β2-agonists (stacked or continuous nebulizers) for refractory bronchospasm
• Fluid resuscitation w/ lg volume of crystalloid (may extravasate up to 35% of blood volume)
• Antihistamines relieve hives & itching, no effect on airway or hemodynamics H1RA (diphenhydramine 50 mg IV/IM) ± H2RA (eg, ranitidine 50 mg IV)
• Corticosteroids have no immediate effect but may help prevent relapse: methylprednisolone 125 mg IV q6h if severe or prednisone 50 mg PO
• Glucagon (1–5 mg IV over 5 min) if inotropic or chronotropic support needed in Pt taking bB
• Avoid unopposed a-adrenergic vasopressors
Disposition
• Mild rxn limited to urticaria or mild bronchospasm can be observed for ≥6 h; admit all others
• Watch for biphasic reaction; occurs in 23%, typically w/in 8–10 h but up to 72 h
• At time of d/c: education re: allergen avoidance, instruction and Rx for EpiPen, allergist f/u