General Medical Information

Management of Allergic Emergencies

Richard L. Mabry

Knowing how to manage anaphylaxis is important for all physicians, even those who do not administer immunotherapy, because the same steps are involved in the proper diagnosis and management of reactions caused by drugs such as penicillin and by insect stings. The physician must first differentiate early anaphylaxis from vasovagal syncope or needle reaction. If syncope is present, placing the patient in a recumbent position and administering an ammonia ampule usually suffices, although oxygen inhalation can afford both physical and psychologic benefit. The use of a flow sheet helps to speed proper treatment and makes omission of important steps less likely. For personnel likely to be involved in assisting with an allergic emergency, drills and training in cardiopulmonary resuscitation are recommended. Expiration dates of drugs and availability of properly operating equipment must be checked regularly.

More deaths of anaphylaxis are caused by airway obstruction than by cardiovascular collapse. After the diagnosis is established, help is summoned, and epinephrine, the mainstay of treatment of anaphylaxis, is administered. The priorities are (a) establishing and protecting an airway, (b) establishing an intravenous line, and (c) administering more epinephrine if needed followed by an antihistamine, a glucocorticoid, and possibly an H2 histamine receptor blocker, all of which further alleviate acute and late symptoms. Heparin has a high capacity for binding histamine and has been shown to have a life-preserving effect in animals given lethal doses of histamine releasers, such as polymyxin, snake venom, or compound 48/80. Slow, intravenous administration of 10,000 U heparin to a patient with otherwise refractory anaphylaxis is appropriate, although not to the exclusion of more conventional measures.

Special circumstances dictate alteration in treatment. Patients taking b-adrenergic blockers appear to be at greater risk of allergic reactions of all causes (immunotherapy, drugs, insect stings). When such reactions are managed with epinephrine, an unopposed a-adrenergic effect can cause extreme hypertension. The physician should not give larger doses of epinephrine to patients taking b-blockers to “break through” unresponsiveness to the drug. Instead, epinephrine should be administered with caution and more dependence placed on other treatment measures. Tricyclic antidepressants and MAO inhibitors also potentiate the a-adrenergic effects of epinephrine. Patients taking these drugs should be treated cautiously.