Anaphylaxis

18 Anaphylaxis



Anaphylaxis is an acute, rapidly progressive, potentially life-threatening systemic allergic reaction. Traditionally, anaphylactic reactions were caused by an immunoglobulin E– (IgE-) mediated mechanism, and “anaphylactoid” reactions were caused by non-IgE mediated mechanisms. More recently, definitions have changed. Anaphylactic reactions are caused by any immune-mediated mechanism (IgE, IgG, or immune complex), and nonallergic anaphylaxis refers to nonimmune-mediated reactions. Regardless of the mechanism, the reactions are indistinguishable. Clinically, patients typically present with varying degrees of dermatologic (e.g., hives), respiratory (e.g., wheezing), gastrointestinal (e.g., vomiting), and circulatory (e.g., hypotension) manifestations. Reactions can range from mild to severe and may be fatal. The most common causes of anaphylaxis in the pediatric population include foods, drugs, venom, and latex. The true incidence of anaphylactic reactions is unknown because of underdiagnosis and underreporting. In the United States, the potential risk of anaphylaxis approximates 1% of the general population. Currently, it is approximated that the death rate of anaphylaxis is 1 to 3 per million people per year.



Etiology and Pathogenesis


IgE-mediated anaphylaxis, a type I hypersensitivity reaction, is the most understood form of anaphylaxis (Figure 18-1). A person is exposed to an antigen, and upon reexposure, cross-linkage of IgE occurs followed by an immediate release of potent mediators from tissue mast cells and peripheral basophils. These mediators include histamine, leukotrienes, nitric oxide, and neutral proteases, which all lead to vasodilatation, increased vascular permeability, bronchoconstriction, and additional inflammation. At times, the reaction occurs with the first known exposure.



Other mechanisms include direct stimulation of mast cells and basophils, as is observed with morphine and exercise- and cold-induced anaphylaxis. Blood products and radiocontrast media may lead to activation of complement and subsequent reactions. Anaphylaxis to aspirin and nonsteroidal antiinflammatory drugs (NSAIDs) may result from the interference of the arachidonic acid pathway. Other agents may act through one or more of the above mechanisms.


The most common IgE-mediated reactions occur with food, drugs, venom, and latex. The leading cause of anaphylaxis in children is food. In the United States, the most common foods implicated in anaphylactic reactions include milk, eggs, soy, wheat, peanuts, tree nuts, and fish (although almost any food can cause a reaction). Children often develop tolerance and outgrow reactions to milk, egg, soy, and wheat; this is less likely to occur with peanuts, tree nuts, and fish. Drug allergy is another common cause of IgE-mediated anaphylaxis, with penicillin and other β-lactam antibiotics being the most commonly implicated agents. Other medications, such as aspirin and NSAIDs, may also lead to reactions. Fire ants and hymenoptera (e.g., honey bees, yellow jackets, hornets, and wasps) are common causes of anaphylaxis in both children and adults. Children with spina bifida and health care workers are at higher risk for latex allergy. Although latex allergy had been on the rise, current use of latex precautions, latex-free gloves, and health care provider awareness have stabilized the incidence of latex reactions. There is also an entity known as exercise-induced anaphylaxis. Three groups of patients present with anaphylaxis after exercising: some of whom have known specific food triggers, others in whom any food ingestion may lead to symptoms, and a third group in which there is no known food trigger. Those with a food trigger have symptoms when they exercise within 4 hours of a meal. Other causes of anaphylaxis include immunizations, radio contrast material, blood products, allergy immunotherapy, and those that remain unknown (idiopathic).



Clinical Presentation


Patients with anaphylaxis may have different clinical manifestations (Table 18-1). Anaphylaxis is often underdiagnosed or misdiagnosed because of clinicians’ failure to recognize symptoms. There has been a recent attempt to standardize the diagnostic criteria to help clinicians to better recognize anaphylaxis (Box 18-1 and Figure 18-2). Approximately 90% of children with allergic reactions have skin manifestations, which include hives, angioedema (see Chapter 20, Figures 20-1 and 20-2), pruritus, or flushing. Although the remainder may not have skin involvement, they are still having a reaction, and that reaction may be more severe than those that occur with skin findings present. Tongue and throat swelling, dysphagia, and choking are manifestations of upper airway edema. Lower respiratory tract symptoms, such as coughing and wheezing, are the next most common symptoms. Vomiting, diarrhea, and abdominal pain are often seen, especially in food-induced anaphylaxis. Cardiovascular manifestations include tachycardia, hypotension, shock, and (rarely) bradycardia. Children may also be lethargic, and some have described a “feeling of impending doom.”


Table 18-1 Signs and Symptoms of Anaphylactic Reactions



























Systems Signs and Symptoms
Cutaneous






Respiratory Upper Respiratory










Lower Respiratory






Cardiovascular




Gastrointestinal



Neurologic




Jun 19, 2016 | Posted by in PEDIATRICS | Comments Off on Anaphylaxis

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