Steve Bensen, age 32, arrives at the nursing triage station breathing heavily and wheezing audibly. His skin is flushed, eyes and lips are swollen. As you help him into a gown, you see wheals on his upper arms.

Mr. Bensen explains that he was at a dinner party, and after a few bites of salad he became nauseated, anxious, and short of breath, and he felt his lips swelling. He says that on his way to the ED his skin became very itchy and red, his hands swollen, and his breathing more difficult. His vital signs are: T, 100.1[degrees]F; BP, 88/56 mmHg; P, 120; R, 28 per minute. On auscultation, you hear diffuse inspiratory and expiratory wheezes throughout.

You immediately obtain IV access and start infusing normal saline. As you prepare to administer oxygen via nonrebreathing mask, his wife tells you he's had two prior episodes of hives after eating peanuts. Ms. Bensen isn't sure, but thinks the salad had a peanut dressing.

DECIPHERING THE CLUES

You are certain that Mr. Bensen is experiencing an anaphylactic reaction, probably in response to the ingestion of peanuts. Anaphylaxis manifests as sudden onset of allergic responses, including hypotension, tachycardia, dyspnea, laryngeal and bronchial edema, urticaria, and angioedema. If not treated immediately, death can result from airway obstruction (secondary to laryngeal edema) or circulatory collapse.

WHAT CAUSES THE PROBLEM

An anaphylactic reaction is triggered by exposure to an allergen via injection, inhalation, ingestion, or skin contact.

Typically in food allergies, the reaction occurs after exposure to a minimal amount of the food in question. Seafood, nuts, eggs, and fruits are the foods that most often precipitate anaphylaxis.

During the first exposure to an antigen, the body produces immunoglobulin E (IgE) antibodies, which bind to the surfaces of mast cells and basophils. With subsequent exposures, the antigen binds to the IgE, bursting the cells and causing the massive release of histamine, leukotrienes, platelet activating factors, kinins, serotonin, and anaphylatoxins throughout the circulatory system. The release of these chemicals initiates a variety of life-threatening responses: vasodilation, increased capillary permeability, increased mucous secretion, and constriction of smooth muscle. These acute systemic reactions generally begin within minutes of exposure to the allergen.

Hypotension results from the dilation of peripheral vessels and the shift of fluid from the intravascular system into the interstitial spaces. Urticaria (edema and vasodilation of the upper dermis that manifest as pruritis and rash) and angioedema (edema of the deep dermis, such as lip and facial swelling) are caused by the release of histamine and a subsequent increase in capillary permeability. Bronchospasm, laryngospasm, and abdominal cramping result from smooth muscle constriction.

HOW TO INTERVENE

Your priority is to maintain the airway and then to improve Mr. Bensen's respiratory status and prevent circulatory collapse. You place Mr. Bensen on high-flow oxygen at 15L/min.

The physician orders epinephrine 0.5 mL, diluted 1:1,000, which you will repeatedly administer SQ every 10 to 20 minutes as needed to promote peripheral vasoconstriction and to slow release of the chemical mediators. If the drop in blood pressure were profound or continuing, the drug could be given IV as a 1:10,000 dilution.

Volume expansion with normal saline or lactated Ringer's solution is critical to maintaining blood pressure; most adults require 1 to 2 liters in the first hour. In the absence of improvement, or if blood pressure continues to fall, an epinephrine drip would be started as a last resort.

Diphenhydramine is ordered at 50 mg IM or IV to counteract the signs associated with histamine release-edema, bronchoconstriction, vasodilation, and pruritus. Corticosteroids are administered IV for their anti-inflammatory effect. Their action is not immediate, but they can prevent recurrence of symptoms hours later. The physician may order the bronchodilator albuterol by nebulizer.

During treatment you tell Mr. Bensen that sympathomimetics such as epinephrine or albuterol can cause restlessness, palpitations, and increased anxiety. After receiving two doses of epinephrine, 50 mg diphenhydramine, IV corticosteroids, oxygen therapy, and IV fluids, Mr. Bensen requires no further intervention. His BP is 128/88 mmHg; P, 92; R, 20 per minute; and he is no longer wheezing. He feels "shaky" but says his breathing is much improved. The edema has dissipated.

FOLLOWING UP

In preparing Mr. Bensen for discharge, you review the importance of avoiding peanuts. You give him a prescription for a three-day course of prednisone and encourage him to drink plenty of fluids to maintain intravascular volume and to counteract the dryness caused by the diphenhydramine. Mr. Bensen's follow-up with his physician will include discussing obtaining an epinephrine syringe for self-administration and consultation with an allergist. You emphasize that anaphylactic reactions are life-threatening, that Mr. Bensen should seek emergency treatment immediately upon exposure, even if he uses an epinephrine injection kit, and, finally, that he should wear a medic-alert bracelet.