UMEM Educational Pearls

Category: Critical Care

Title: I just gave IM Epi for anaphylaxis, how long do I need to observe the patient?

Keywords: epinephrine, im, anaphylaxis, allergic reaction, observation (PubMed Search)

Posted: 7/29/2014 by Feras Khan, MD
Click here to contact Feras Khan, MD

Observation after giving IM Epi for allergic reactions or anaphylaxis


  • Common practice is to observe patients who receive epinephrine for allergic reactions or anaphylaxis for several hours post-administration
  • This can be from 4-24 hours depending on the institution
  • This is to monitor for a biphasic reaction


  • Do we need to observe these patients?
  • And if so, for how long?


  • 2 urban Canadian EDs
  • 5 year period
  • Primary outcome was the amount of patients with a clinically important biphasic reaction
  • Secondary outcome was mortality


  • 2819 encounters: 496 anaphylactic + 2323 allergic reactions
  • 5 clinically important biphasic reactions (0.18%; 95% CI 0% to 0.17%)
  • No fatalities
  • Biphasic reactions tended to happen several hours (>24hrs) after ED discharge


  • If patients did not return to an ED in the region, then they would not be identified as a possible biphasic reaction

What to do?

  • You can probably discharge most patients whose symptoms have resolved without a prolonged observation period (<4hrs)
  • Patients with ongoing anaphylaxis and allergic reaction, should be observed longer or admitted
  • Biphasic reactions are very rare


Grunau B, et al. Incidence of Clinically Important Biphasic Reactions in Emergency Department Patients with Allergic Reactions or Anaphylaxis. Annals of Emergency Medicine. Vol 63, No 6; June 2014 736-743.