Five patients (0.18 percent) were identified as having clinically important biphasic reactions (95% confidence interval [CI], 0.07% to 0.44%). Two of these reactions occurred during the ED visit and three postdischarge (28 hours, 35 hours, and 143 hours). There were no fatalities (95% CI, 0% to 0.17%).

EBM Comments

This was a very well-done retrospective chart review of consecutive adult patients presenting to the ED with allergic reaction or anaphylaxis (see Table 1). They followed the methods described by Gilbert et al and Worster et al.^4,5

The study is limited by the retrospective nature. There was no defined protocol for managing allergic reactions. Some patients may have been missed if they presented to their primary care provider or left the province. There also could have been patients miscoded as shock on their second presentation rather than allergic reaction.

Bottom Line

Prolonged observation is likely unnecessary in patients whose symptoms resolve with therapy in the ED. Biphasic reactions are rare and can occur anywhere from 10 minutes up to six days after an initial reaction.

Case Resolution

The woman is observed for three hours after being treated for her anaphylactic reaction. She is doing well, with no vomiting, no shortness of breath, and resolving hives. She is discharged home with an epinephrine auto injector and oral corticosteroids, told to avoid triggers, and given an allergic reaction tool kit.⁶

Thank you to Anand Swaminathan MD, MPH, assistant program director in the department of emergency medicine at NYU/Bellevue Hospital for his help with this review.⁷

Remember to be skeptical of anything you learn, even if you learned it on The Skeptics Guide to Emergency Medicine.

Dr. Milne is chief of emergency medicine and chief of staff at South Huron Hospital, Ontario, Canada. He is on the Best Evidence in Emergency Medicine faculty and is creator of the knowledge translation project the Skeptics Guide to Emergency Medicine (www.TheSGEM.com).

References

1. Guidelines for the diagnosis and management of food allergy in the United States. J Allergy Clin Immunol. 2010;26:S1-58.
2. Simons F, Ardusso L, Bilò, M, et al. World Allergy Organization Guidelines for the assessment and management of anaphylaxis. Curr Opin Allergy Clin Immunol. 2012;12:389–99.
3. Tole JW, Lieberman P. Biphasic anaphylaxis: review of incidence, clinical predictors and observation recommendations. Immunol Allergy Clin N Am. 2007;27:309-26.
4. Gilbert EH, Lowenstein SR, Koziol-McLain J, et al. Chart reviews in emergency medicine research: where are the methods? Ann Emerg Med. 1996;27:305-8.
5. Worster A, Bledsoe RD, Cleve P, et al. Reassessing the methods of medical record review studies in emergency medicine research. Ann Emerg Med. 2005;45:448-51.
6. Anaphylaxis tool kit. Available at: https://www.allergicreactiontoolkit.com. Accessed Nov. 18, 2014.
7. Rezaie S. Episode 1. REBEL-EM Cast. Available at: http://rebelem.com/rebelcast-episode-1. Accessed Nov. 18, 2014.