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  • Anaphylaxis is an acute, systemic, and potentially fatal hypersensitivity reaction with variable presentation including cutaneous, respiratory cardiovascular, and/or gastrointestinal manifestations.

  • It is rapid in onset with symptoms developing 5-30 minutes after exposure to allergen, though in some cases it can be as long as few hours.

  • Cutaneous symptoms are common but hemodynamic collapse and shock can occur in the absence of these.

  • The prevalence of anaphylaxis is increasing, as are hospitalizations for anaphylaxis; however, fatality rates are stable.

  • Rapid administration of intramuscular epinephrine is the first-line treatment of choice for both in-hospital and out-of-hospital treatment.

  • The most common triggers for anaphylaxis in the outpatient setting are foods, medication, and insect venom. The majority of anaphylaxis presenting to the emergency room is due to food. Medications are the most common cause of inpatient anaphylaxis.

  • Risk factors for anaphylaxis include asthma, atopy, pregnancy, cardiovascular disease, and other comorbidities.

  • Cofactors including exercise, alcohol, stress, infection, and medications such as nonsteroidal anti-inflammatory drugs, β-blockers, and angiotensin-converting enzyme inhibitors may increase both risk and severity of reactions.

  • Serum tryptase can be helpful in confirming anaphylaxis but careful history and physical examination are the most important factors in the diagnosis of anaphylaxis.

  • Anaphylaxis is the most severe and potentially fatal form of immediate hypersensitivity reaction. Prompt recognition, administration of epinephrine, and intravascular volume replacement are key to preventing potentially fatal outcomes.


Anaphylaxis is an acute and potentially fatal allergic reaction with variable presentation including cutaneous, respiratory cardiovascular, and/or gastrointestinal manifestations.1,2 In the past, reactions mediated by IgE antibody were classified as anaphylactic and those that were non-IgE, mediated as anaphylactoid; however, the term anaphylactoid has fallen out of favor as the varied pathophysiologic pathways involved in anaphylaxis have elucidated.2 Familiarity with the signs and symptoms of anaphylaxis and the differential diagnosis is essential for every urgent and critical care health care provider. Severe anaphylaxis is characterized by potentially life-threatening compromise in breathing and/or circulation, and may occur without typical skin features or circulatory shock being present.1 Although not every case of anaphylaxis is life-threatening, predicting severe reactions is not possible, and there is evidence that early administration of epinephrine may reduce risk, making rapid recognition vital for timely life-saving treatment.1,2 The clinical diagnostic criteria provided by the National Institute of Allergy and Infectious Diseases (NIAID) provides a framework for clinicians to quickly evaluate for anaphylaxis and has a sensitivity of 95% and specificity of 71% (Box 131-1).

Box 131-1 Diagnostic Criteria for Anaphylaxis

Anaphylaxis is highly likely when any of the following two criteria are fulfilled:

  1. Acute onset of an illness (minutes to several hours) with simultaneous involvement of the skin, mucosal tissue, or both (eg, generalized hives, pruritus or flushing, swollen lips-tongue-uvula)


    1. Respiratory compromise (eg, dyspnea, wheeze-bronchospasm, stridor, reduced peak expiratory flow, hypoxemia)

    2. Reduced blood pressure or associated ...

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