Anaphylaxis

Definition

• Life-threatening IgE-mediated allergic reaction affecting multiple organ systems

Pathophysiology

• Allergen epitopes interacti with IgE on mast cells of basophils
• This causes degranulation and the release of tryptase, TNF-alpha, and histamine

NIAID/FAAN Criteria

• Any one of the three following criteria:
  • Acute onset of illness with involvement of (with or without an allergen):
    • Skin/mucosa (pruritus, flushing, hives, angioedema)
    • And either:
      • Respiratory compromise (dyspnea, decreased PEF, stridor, hypoxemia)
      • Hypotension or end-organ dysfunction (collapse, syncope, incontinence)
  • Two or more of the following occurring after a likely allergen exposure:
    • Skin/mucosa (pruritus, flushing, hives, angioedema)
    • Respiratory compromise (dyspnea, decreased PEF, stridor, hypoxemia)
    • Hypotension or end-organ dysfunction (collapse, syncope, incontinence)
    • Persistent GI symptoms (vomiting, crampy abdo pain, diarrhea)
  • Hypotension after exposure to a known allergen

Clinical Presentation

• History
  • Co-factors that augment anaphylaxis:
    • Exercise
    • NSAIDs
    • Alcohol
    • URTI
    • Premenstruation
• Signs & Symptoms

Investigations

• Serum tryptase

Management

Acute

• IV, O2, monitor
• Remove allergen, including any IVs that might be running allergen
• Intramuscular epinephrine 1:1000 0.01mg/kg (max 0.5mg) IM q5-15min for 3 doses, if needed
• Large-volume IV fluids
• Add vasopressors or glucagon if persistent hypotension
  • Start epinephrine infusion 2-10mcg/kg/min
  • Reverse beta-blocker if necessary with 1-5mg IV glucagon
• Place supine (or left decubitus if pregnant)
• Supplemental oxygen; consider airway management
• Consider salbutamol for bronchospasm

Subacute

• Ranitidine 50mg IV; diphenhydramine 25-50mg IV
• There is a risk of biphasic reaction 8-72 hours after resolution
  • Methylprednisolone 125mg IV
• Observe for 4-8 hours
• Prescribe epinephrine autoinjectors
• Arrange follow-up with allergist

Chronic

• Epi-Pen
• Desensitization, when appropriate