Anaphylaxis

Anaphylaxis

 

Anaphylaxis is an acute, potentially fatal allergic reaction involving the respiratory, skin, circulatory, and immune systems.

Epidemiology

  • Prevalence – 75/100,000 lifetime incidence
  • Age – spans all age groups
  • Sex – M:F; equal

Risk Factors

  • Previous history of anaphylaxis; hives or urticaria following allergen exposure

Pathophysiology

  • Involves activated mast cell release of multiple substances – cytokines, histamine, tryptase, prostaglandins
  • Some forms are IgE mediated; others are not
    • IgE mediated
      • Medications
      • Foods
      • Insect venoms
    • IgE independent
      • Cold, heat
      • Drugs – opioids, muscle relaxants, NSAIDS, ACE inhibitors
      • Exercise
      • Radiocontrast media
  • Interval to anaphylaxis depends on allergen
    • Food – 25-30 minutes after ingestion
    • Drugs – 10-20 minutes after administration
    • Insect stings – 10-15 minutes after sting
    • Blood or blood products in IgA deficient patients (no detectable level)

Clinical Presentation

  • Respiratory – dyspnea, tachypnea, bronchospasm, laryngeal or tongue edema
  • Cardiovascular – tachycardia, hypotension, cardiac arrhythmias, angina, cardiac arrest
  • Gastrointestinal – nausea, abdominal cramps, emesis, diarrhea
  • Cutaneous – erythema, generalized pruritus, urticaria, angioedema
  • Other – rhinitis, cramps, dizziness, syncope

Diagnosis

  • Clinical history and examination consistent with anaphylaxis
  • Laboratory testing
    • Serum tryptase
      • Levels peak 1 hour after onset of anaphylaxis
      • Elevation persists for 4-6 hours
    • Serum or plasma histamine
      • Levels peak 5 minutes after onset of anaphylaxis
      • Return to baseline levels within 30-60 minutes
      • May be elevated in serum due to artifactual basophil activation during clotting
    • Urine histamine
      • Levels of a histamine metabolite, N-methylhistamine, remain elevated in the urine for many hours after anaphylaxis
      • Reflects overall levels of released histamine
    • Appropriate IgE testing
      • Single IgE level may be helpful
      • Multiple allergen IgE testing based on suspicion of allergen
      • No recommendations for broad IgE testing
      • Caution – in vitro IgE detection may not correlate with anaphylaxis potential of an allergen

Differential Diagnosis

  • Vasovagal reaction
  • Panic attack
  • Flush syndrome
  • Hereditary or acquired angioedema
  • Other forms of shock
  • Systemic mastocytosis

Treatment

  • Immediate
    • Epinephrine
    • Antihistamines
    • Corticosteroids
  • Observation after initial treatment, fluid administration

Prevention

  • Avoidance of known allergens
  • Use of epinephrine pens when exposed to known allergen; epinephrine should be available at all times for possible repeat exposures
  • Desensitization for insect stings

See Also