If you do give steroids, I recommend a single 10 mg dose of dexamethasone in the emergency department, which has the advantage of a long half-life of 53 hours, thus negating the need for prescribing steroids upon discharge.

Some patients who present to the emergency department with anaphylaxis in shock require IV epinephrine. After two IM doses of 0.01 mg/kg (max 0.5 mg) epinephrine five minutes apart, give IV epinephrine:

• Inject 1 mg of epinephrine 1:10,000 into a 1 L bag of normal saline
• Draw up 10 mL from the 1 L bag in a 10 mL syringe

Push dose: 10 mL every two to five minutes (10 mcg)

Dose of epinephrine given via infusion: 1 mL/min (1 mcg/min) and titrate to a maximum of 20 mL/min

Do not underestimate the profound vasodilatory shock that may accompany anaphylactic shock. Aggressive fluid resuscitation is indicated for patients with anaphylactic shock. Consideration may be given to a second vasopressor with alpha properties such as vasopressin.

One of the more common causes of death in anaphylaxis is patients failing to self-administer the epinephrine auto-injector (even if they’re carrying it on their person) or not administering it properly. It is, therefore, imperative to take the time to counsel patients before they leave the emergency department: Carry two epinephrine auto-injectors (many patients will require two doses), be sure that the blue end points away and the orange end points to the thigh (“blue to the sky, orange to the thigh”), and hold the auto-injector firmly in place against the thigh for 10 seconds.

Observation Time in Anaphylaxis

Traditionally, patients with anaphylaxis are observed in the emergency department for four to six hours before discharge. However, there’s no literature to support this practice. Some experts recommend observing patients until they become asymptomatic regardless of time. It may be prudent to observe patients who are at high risk for severe anaphylaxis for a longer time, including patients taking antihypertensive medications, with an early symptom onset/late treatment initiation, with asthma, and with a past history of severe reactions.

Biphasic reactions in anaphylaxis can occur any time between one hour and seven days after the initial anaphylactic episode in approximately 2 to 5 percent of patients. Recent literature has found that the rate of biphasic reactions may be lower than previously thought, biphasic reactions rarely result in death, and the number needed to treat (NNT) with steroids to prevent one ED relapse visit is 176. However, these studies have included not only patients with true anaphylaxis but also those with simple allergic reactions who did not receive epinephrine. Many of these patients would have gotten better by themselves regardless of medications.