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Anaphylaxis is a rapidly developing, life-threatening systemic reaction mediated by the release of mast cell and basophil-derived mediators into the circulation. The peak severity is seen usually within 5–30 minutes.
- Allergic IgE-mediated anaphylaxis (type 1 hypersensitivity)
- IgG-mediated anaphylaxis (rare)
Nonimmunologic anaphylaxis. Previously known as anaphylactoid reactions.
Incidence of anaphylaxis is approximately 50–2000 episodes per 100,000 person-years. Fatality is estimated at 0.7%–2% per case of anaphylaxis. In the United States, the lifetime prevalence of anaphylaxis is reported to be 1.6%.1
- Foods, especially peanuts, tree nuts, shellfish, finned fish, milk, and eggs
- Insect stings (bees, wasps, and fire ants)
- Latex rubber
- Blood products
- Radiocontrast media
- Medications (i.e., NSAIDs, opiates, vancomycin, muscle relaxants, rarely ACE inhibitors, and sulfating agents)
- Physical factors (cold temperature or exercise)
- Anaphylaxis is due to sensitization to an antigen and formation of specific IgE to that antigen. On re-exposure, the IgE on mast cells and basophils binds the antigen and cross-links the IgE receptor, which causes activation of the cells with subsequent systemic release of preformed mediators, such as histamine.
- The release of mediators ultimately causes capillary leakage, cellular edema, and smooth muscle contractions resulting in the constellation of physical symptoms.
Nonimmunologic. Non–IgE-mediated anaphylaxis is also mediated by direct degranulation of mast cells and basophils in the absence of immunoglobulins.
- Persistent asthma: increased risk of fatal anaphylaxis if asthma is uncontrolled.
- Cardiovascular disease: increased risk for death in older age.
- Elevated baseline tryptase indicates possible mast cell disorder. Individuals with mastocytosis, a disease characterized by a proliferation of mast cells, are at higher risk for severe anaphylaxis from both IgE- and non–IgE-mediated causes.
- Previous sensitization and formation of antigen-specific IgE with history of anaphylaxis.
- Concomitant use drugs: beta-adrenergic blockers, ACE inhibitors, NSAIDs, alcohol, etc.
- Cofactors such as exercise, fever, acute infection, premenstrual status, and emotional.
- Sensitivity to seafood or iodine does not predispose to radiocontrast media reactions.
- For all types of anaphylaxis, recognition of potential triggers and avoidance are the best prevention.
- Self-injectable epinephrine and patient education for all patients with a history of anaphylaxis.
- Radiocontrast sensitivity reactions
- Use of low-ionic contrast media is strongly suggested.
- Premedication before procedure.
- Prednisone 50 mg PO given 13, 7, and 1 hour before procedure.
- Diphenhydramine 50 mg PO given 1 hour before procedure.
- H2 blocker may also be given 1 hour before procedure.
- Premedication is not 100% effective, and appropriate precautions for handling a reaction should be taken.
- Anaphylaxis can be a presenting sign of underlying mastocytosis.
- Red man syndrome from vancomycin. Symptoms can usually be prevented by slowing the rate of infusion and premedicating with diphenhydramine (50 mg PO) 30 minutes before start of the infusion.