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August 5, 2019 at 12:54 am
Patient with ongoing symptoms of anaphylaxis or severe symptoms (e.g. angioedema, respiratory distress) concerning for airway compromise, should be admitted for a period of observation, even if they are stabilized in the ED. However, those with more mild symptoms that responded well to initial epinephrine can be discharged with allergist follow-up. There are no clear guidelines as to the duration of this ED observation period, although an anaphylaxis practice parameter recommends observation for at least 4 to 8 hours. The period of observation is meant to identify any biphasic reaction. Biphasic reactions are rare (4%) though. Some risk factors for biphasic reaction are: history of prior anaphylaxis, unknown precipitating trigger, first epinephrine dose > 60 minutes after symptoms started, and possibly symptoms of diarrhea or wheezing.
References:
Campbell RL et al. Emergency department diagnosis and treatment of anaphylaxis: a practice parameter. Ann Allergy Asthma Immunol 2014;113:599-608
Lee S et al. Predictors of biphasic reactions in the ED for patients with anaphylaxis. J Allergy Clin Immunol Pract 2014;2:281-7
Lee S et al. Further evaluation of factors that may predict biphasic reactions in anaphylaxis patients. J Allergy Clin Immunol Pract 2017;5:1295-1301