Anaphylaxis (Table 10) is a Type I hypersensitivity reaction. Initial exposure to an allergen results in antigen-specific antibody production dominated by the immunoglobulin E (IgE) isotype. Following re-exposure, IgE antibodies bind to mast cells and basophils associated with mucosal and epithelial tissues. The simultaneous binding of an antigen to adjacent IgE molecules fixed to Fc receptors triggers degranulation of mast cells and basophils resulting in the release of histamine, leukotrienes, prostaglandins, chemokines, enzymes and cytokines in target tissues.

Table 10. Anaphylaxis.

  • Identify at-risk patient
    • A negative history of prior anaphylactic reaction does not rule out the possibility of a type I allergic reaction
Signs and symptoms:
  • 1 to 15 minutes following exposure to a specific allergen
    • Pruritus, urticaria, angioedema
    • Coughing, stridor, dyspnea, wheezing,
    • Agitation, flushing, palpitation
    • Unresponsiveness, convulsion,
    • Hypotension, cardiogenic shock
Emergency response:
  • Place patient in a supine position
    • Activate EMS
      • Immediately administer epinephrine 1:1000
        • Adult: epinephrine (EpiPen), 0.3 mg, IM (anterolateral thigh)
        • Child: epinephrine (EpiPen Jr), 0.15 mg, IM (anterolateral thigh)
      • If the patient does not respond to the initial dose of epinephrine and the arrival of EMS will exceed 5 to 10 minutes, a repeat dose may be administered
        • Patients with stridor and wheezing unresponsive to epinephrine should be given O2
          • 4 to 6 L/minute by nasal cannula
        • Monitor vital signs
          • If at any time the patient becomes unresponsive, no normal breathing, and no palpable pulse consider the diagnosis of cardiac arrest
            • Immediate CPR and defibrillation congruent with current recommendations
Nota bene:
  • Signs of recovering: character of respiration returns to normal, vital signs return to baseline values
  • Signs of deterioration: loss of consciousness, breathing unstable, vital signs labile
  • For patients with cardiovascular diseases and/or diabetes mellitus, start treatment with smaller doses of epinephrine
    • Paradoxically, patients taking beta-adrenergic blocking agents may require more epinephrine to reverse the effects of anaphylaxis.