9. Anaphylaxis

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Anaphylaxis is an acute-onset, potentially fatal systemic allergic reaction. It is usually triggered by an agent such as an insect sting, food, or medication, through a mechanism involving IgE and the high-affinity IgE receptor on mast cells or basophils. Less commonly, it is triggered through other immunologic mechanisms, or through nonimmunologic mechanisms. It often occurs in community settings. Anaphylaxis episodes range in severity from those that are mild and resolve spontaneously to those that are fatal within minutes. The clinical diagnosis is based on a meticulous history and physical examination, sometimes, but not necessarily, supported by a laboratory test such as an elevated serum total tryptase level. Sensitization to allergen triggers suggested by the history needs to be confirmed by skin testing and measurement of allergen-specific IgE. In some sensitized individuals, additional tests are needed to assess the risk of future anaphylaxis episodes. Prompt injection of epinephrine is life-saving. H1-antihistamines and inhaled β2-adrenergic agonists cannot be depended on to prevent fatality. Long-term risk reduction is an integral part of management.

Section snippets

Pathogenesis

In many individuals with anaphylaxis, IgE plays a pivotal role. Synthesized in response to allergen exposure, it becomes fixed to FcɛRI on the surface membranes of mast cells and basophils. Aggregation of receptor-bound IgE molecules on re-exposure to the allergen results in cell activation, mediator release, and the immediate hypersensitivity response. IgE also contributes to the intensity of anaphylaxis through mechanisms that go beyond sensitizing, priming, activation, and mediator release;

Diagnosis

Diagnosis of anaphylaxis depends primarily on a meticulous clinical history: ascertaining exposure to potential triggering agents or events, time elapsed between exposure and symptom onset, and evolution of the episode over minutes or hours. Among individuals recognized as having anaphylaxis, target organs include skin (90% of episodes), respiratory tract (70%), gastrointestinal tract (30% to 45%), cardiovascular system (10% to 45%), and central nervous system (CNS; 10% to 15%; Fig 1, A).

Management

When anaphylaxis occurs in a healthcare facility, rapid assessment of airway, breathing, circulation, and orientation is mandatory; in addition, the skin should be examined and body weight (mass) should be estimated. This should be followed by prompt intramuscular injection of epinephrine, administration of supplemental oxygen, establishment of an airway, placing the individual in the supine position, and insertion of 1 or more large-bore intravenous lines for fluid replacement and infusion of

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    Disclosure of potential conflict of interest: The author has declared that she has no conflict of interest.

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