Anaphylaxis is common in the ED. These patients are treated and then usually watched for 4-6 hours.
Biphasic happens in patients that have a complete resolution of their anaphylaxis for at least an hour, but then have a recurrence that requires pharmacologic intervention. Most of the time this happens 3-6 hours later, but can happen more than 10 hours later.
More commonly happens in patients that have a delayed presentation, a wide pulse pressure, need multiple doses of epi, require the use of a beta agonist, or are ages 6-9 years old.
Educate patients about the possibility of Biphasic anaphylaxis before discharge.