The diagnosis of anaphylaxis is usually apparent from the acute and often dramatic onset of multisystem involvement of the skin, respiratory tract, and cardiovascular system. Sudden cardiovascular collapse in the absence of cutaneous symptoms suggests vasovagal collapse, seizure disorder, aspiration, pulmonary embolism, or myocardial infarction. Laryngeal edema, especially with abdominal pain, suggests HAE. Many patients with anaphylaxis are initially thought to have septic shock (see Chapter 40).
Avoidance of triggering agents is important in the management of urticaria and angioedema. The mainstay of pharmacologic treatment is H1 antihistamines. Second-generation H1 antihistamines, such as cetirizine, desloratadine, fexofenadine, levocetirizine, and loratadine, are preferred because they have fewer adverse effects. If a second-generation H1 antihistamine, by itself, does not provide adequate relief, the next step is to add a sedating H1 antihistamine at bedtime or H2 antihistamines, such as cimetidine or ranitidine. Tricyclic antidepressants, such as doxepin, exhibit potent activity at both H1 and H2 receptors. Corticosteroids are effective in treating urticaria and angioedema, although adverse effects from long-term use mandate the lowest dose for the shortest time. When urticaria is resistant to treatment, the leukotriene receptor blocker montelukast has been used in several case studies. Other immunomodulating agents, such as cyclosporine, hydroxychloroquine, methotrexate, cyclophosphamide, and intravenous immunoglobulin, have been used; however, data supporting their use are limited, and they require laboratory monitoring due to potential adverse effects.
Anaphylaxis is a medical emergency; prompt recognition and immediate treatment are crucial (Fig. 81-2). Early administration of intramuscular epinephrine is the mainstay of therapy and should be given at the same time that basic measures of cardiopulmonary resuscitation are being performed. If the child is not in a medical setting, emergency medical services should be called. Supplemental oxygen and intravenous fluid should be administered with the child lying in supine position. An airway must be secured; intubation or tracheotomy may be required. Additional pharmacologic therapies, such as corticosteroids, antihistamines, H2-receptor antagonists, and bronchodilators, may be given to improve symptoms. Up to 20% of people with anaphylaxis have biphasic or protracted anaphylaxis.
A person with biphasic anaphylaxis has both earlyandlate-phase reactions. The biphasic reaction is a recurrence ofanaphylactic symptoms after an initial remission, occurringwithin 8 to 72 hours after the initial reaction. A person with protracted anaphylaxis has signs and symptoms that persist for hours or even days despite treatment, although thisis rare.
Prevention of urticaria, angioedema, and anaphylaxis focuses on avoidance of known triggers. A referral to an allergy specialist for a thorough history, diagnostic testing, and recommendations for avoidance is suggested for patients following severe reactions or anaphylaxis. Skin testing and serum IgEspecific testing are available for foods, inhalants, insect venoms, drugs (penicillin), vaccines, and latex. Educating the patient and family members about the signs and symptoms of anaphylaxis and using self-administered epinephrine early result in better outcomes. Fatal anaphylaxis has occurred despite timely and appropriate treatment. A MedicAlert bracelet with appropriate information should be worn. Medications such as β-blockers, angiotensin-converting enzyme inhibitors, and monoamine oxidase inhibitors should be discontinued because they may exacerbate anaphylaxis or interfere with its treatment.