Angioedema: Swelling of the lips, periorbital region, face, hands, or feet. Anaphylactoid reactions: Similar clinical picture to anaphylaxis but not caused by immunologic mechanisms. Anaphylaxis: Syndrome with varied mechanisms, clinical presentations, and severity that is an acute life-threatening reaction resulting from an immunologic IgE-mediated mechanism.
Common causes of anaphylaxis include drugs, hymcnoptera slings, radiographic contrast media (anaphylactoid), blood products, latex in medical products, allergen immunotherapy injections, and foods. The most common cause of drug-related anaphylaxis is (3-lactam antibiotics such as penicillins. The most common cause of food-related anaphylaxis is peanuts, partly because of the frequency with which peanut products are included in other types of foods. However, it is important to note that almost any agent that can activate mast cells or basophils can cause an anaphylactic reaction. Approximately one third of all cases of anaphylaxis are idiopathic.
The clinical presentation of anaphylactic reactions varies greatly, but the following guidelines are a good rule of thumb. Symptoms usually develop within 5-60 minutes following exposure, although a delayed reaction is possible. Symptoms and signs are variable and are listed in Table 48-1. The key fact to remember is that a true anaphylactic reaction is life-threatening. Angioedema may occur with or without urticaria but is not anaphylaxis unless the reaction is associated with other life-threatening processes, such as hypotension or laryngeal edema.
Treatment of anaphylaxis begins with first assessing the ABCs (airway, breathing. circulation). Intubation, if required, should not be delayed. Second, epinephrine should be administered to help control symptoms and blood pressure. Intramuscular epinephrine injected in the anterolateral thigh leads to more rapid and higher peak levels than does either subcutaneous or deltoid intramuscular injection. Additional treatment measures include placing the patient in a recumbent position, elevating the legs, administration of oxygen as needed, normal saline volume replacement and/or pressors as required, and administration of diphenhydramine 50 mg oral or intravenously every 4 hours as needed (Table 48-2).
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