Pocket Medicine

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