Title: 410: Incidence of Biphasic Reaction and Need for Hospitalization In Patients Admitted to an Emergency Department Observation Unit After Evaluation for Anaphylaxis
Abstract: Anaphylaxis is a potentially life-threatening allergic reaction commonly managed in the emergency department (ED). Biphasic reactions have been reported to occur in 1-23% of patients. Guidelines recommend patient observation after anaphylaxis, but very little data is available describing patient outcomes. We sought to determine the incidence of biphasic reactions and need for interventions or hospital admission in patients admitted to the ED observation unit (EDOU) after evaluation for anaphylaxis. A retrospective cohort study was conducted from April 2008-March 2010 in an academic ED setting with approximately 80,000 ED visits per year. Adult patients admitted to the EDOU after ED evaluation for anaphylaxis were included. All patients met National Institutes of Allergy and Infectious Diseases/Food Allergy and Anaphylaxis Network (NIAID/FAAN) criteria for anaphylaxis. Data was collected on patient demographics, inciting allergens, symptoms, management, length of stay, incidence of biphasic reactions and disposition. A total of 174 patients met NIAID/FAAN criteria during the study period. Of these 58 (33%) patients were admitted to the EDOU and were included. Median age was 37.3 years (IQR 29-51) and 34 (59%) were female. The inciting allergens were food in 17 (29.3%), medications in 14 (24.1%), insect stings in 9 (15.5%), unknown in 10 (17.2%), and other in 8 (13.8%). Median length of stay during the initial ED evaluation was 1.8 hours. In the ED, 30 patients (51.7%) received epinephrine, with repeat dosing in 2 patients. H1 blockers were given to 57 (98%) patients, 44 (76%) received H2 blockers, 57 (98%) received steroids, and 22 (38%) received bronchodilators. In the EDOU, median length of stay was 5.3 hours (IQR: 3.8 - 7.9), where 36 (62%) patients received additional H1 blockers, 8 (13.1%) received H2 blockers, 7 (12.1%) received steroids, and 2 (3.4%) patients had bronchodilators. Medications were given for symptom recurrence or as continued therapy for the initial reaction. Hospital admission occurred in 4 (6.9%) patients, with one requiring intensive care. Eight (13.8%) patients had a biphasic reaction. Six (75%) of the patients who had a biphasic reaction, had onset of the biphasic symptoms while in the EDOU with time of onset ranging from 1.5 - 5.2 hours after initial symptom resolution. Ultimately, 4 of the 8 patients received epinephrine for the biphasic reaction. Two received epinephrine in the EDOU. The third patient had multiple mild recurrent symptoms in the EDOU that had resolved prior to EDOU dismissal. The patient returned to the ED 4.5 hours later, received epinephrine and was admitted. The fourth patient had no symptoms in the EDOU, but had a multi-day reaction requiring epinephrine on day 3 and was admitted. No evidence currently predicts a biphasic reaction. The utilization of the EDOU after evaluation for anaphylaxis allows observation time without impeding patient flow and avoids unnecessary hospitalizations. In our study, 75% of biphasic reactions occurred within 1.5-5.2 hours during the EDOU stay. This is within the recommended 4-6 hours observation guideline. Our study is limited by the retrospective design but suggest that EDOU utilization after evaluation for an anaphylactic reaction is effective. Prospective studies are needed.