Chapter 68

High-Yield Facts

• More than 50% of anaphylaxis cases are idiopathic; therefore, a high index of suspicion is needed to make the diagnosis in children.

• Airway compromise can occur rapidly.

• Epinephrine is the first-line medication for the treatment of moderate-to-severe anaphylaxis.

• In severe anaphylaxis if 2 to 3 fluid boluses (20 cc/kg) are given, as well as epinephrine; if hypotension persists, an epinephrine drip is indicated.

Anaphylaxis is a severe, potentially life-threatening hypersensitivity reaction characterized by skin or mucosal manifestations that include a pruritic rash, urticaria, or angioedema, respiratory compromise associated with airway edema and bronchospasm, and/or cardiovascular compromise that can result in distributive shock. It occurs within minutes to hours after exposure to an offending allergen. The estimated risk of anaphylaxis per person in the United States is 0.05% to 2%; this likely is an underestimate of the true severity of the problem due to underdiagnosis and underreporting.1 Food allergy is the most common cause of anaphylaxis and is increasing in prevalence.2 Anaphylaxis from food allergy leads to approximately 150 fatalities in the United States each year, and the more rapid the onset of symptoms, the more likely the reaction will be life threatening.3,4 In over 50% of anaphylaxis cases no precipitating cause is identified, therefore the emergency physician must have a high level of suspicion for the disorder to recognize the symptoms and initiate proper treatment.5 Asthma is known to have a strong association with anaphylaxis which may aid in more rapid diagnosis.2,6,7

Pathophysiology

Anaphylaxis is an immunologic reaction. An initial exposure to an allergen results in the development of a specific IgE antibody to the antigen. The IgE antibody resides on the cell membrane of basophils and mast cells. When a subsequent exposure to the allergen occurs, the allergen binds to the IgE on the basophil and mast cells, and stimulates the release of multiple mediators, including histamine, leukotriene C4, prostaglandin D2, and tryptase. These mediators lead to increased production and release of respiratory secretions, increased bronchial smooth muscle tone, decreased vascular smooth muscle tone, and increased capillary permeability. An anaphylactoid reaction involves the release of similar mediators without involvement of the immune system. Intravenous (IV) contrast allergy is an example of an anaphylactoid reaction.

Allergens

Food is the number one cause of anaphylaxis. More than 90% of food-related anaphylaxis is caused by exposure to nuts and shellfish.8,9 In infants, cow's milk and eggs are the most common causes of anaphylaxis.10 Once the food that caused the anaphylaxis is identified, thorough education of the parents and child is necessary to avoid reexposure. Although there has been an increase in hospital admissions due to food-related anaphylaxis, fatalities have remained stable.2,6

Insect stings are a common cause of a localized allergic reaction and can also ...

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