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Information

  1. Anaphylaxis is a life-threatening allergic reaction. It is initiated by antigen binding to preformed IgE antibodies on the surface of mast cells and basophils, which cause release of vasoactive substances (eg, histamine, leukotrienes, prostaglandins, kinins, and platelet-activating factor). Anaphylaxis is characterized by an acute elevation in tryptase levels.
  2. Anaphylactoid reactions are clinically similar to anaphylactic reactions, but they are not mediated by IgE and do not require prior sensitization to an antigen.
  3. Clinical features of anaphylactic or anaphylactoid reactions may include the following:
    1. Urticaria and flushing.
    2. Bronchospasm or airway edema, which can produce respiratory failure.
    3. Hypotension and shock due to peripheral vasodilation and increased capillary permeability.
    4. Pulmonary edema.
  4. Treatment
    1. Discontinue anesthetic agents if circulatory collapse is present.
    2. Administer 100% oxygen. Assess the need to intubate and support ventilation. Airway edema can persist beyond the acute event.
    3. Begin intravascular volume expansion.
    4. Treat hypotension by giving epinephrine 50 to 100 μg IV. For overt cardiovascular collapse, epinephrine 0.5 to 1.0 mg IV is indicated, followed by an infusion if hypotension persists. Epinephrine is useful for treating hypotension and bronchospasm and for limiting mast cell degranulation. Other catecholamines such as norepinephrine may be added. Vasopressin should be added in refractory causes.
    5. Steroids (eg, hydrocortisone 250 mg to 1.0 g IV, or methylprednisolone 1-2 g IV) may reduce the inflammatory response.
    6. Histamine antagonists (eg, diphenhydramine 50 mg IV and ranitidine 50 mg IV in the adult) may be useful as second-line therapy.
    7. Consider drawing a tryptase level after stabilization of the patient to aid in final diagnosis.
  5. Prophylaxis for drug hypersensitivity reactions
    1. Histamine (H1) antagonists. Diphenhydramine 0.5 to 1.0 mg/kg or 50 mg IV in the adult the night before and morning of exposure.
    2. H2antagonists. Ranitidine 50 mg IV or 150 mg orally in the adult the night before and the morning of exposure.
    3. Corticosteroids.Prednisone 1 mg/kg or 50 mg for adults, four doses every 6 hours before exposure.