Methods: A multicenter retrospective cohort study was conducted for ED visits from January - December 2010. All visits that satisfied anaphylaxis diagnostic criteria of the NIAID/FAAN were included. We analyzed the predictors of biphasic reaction using univariate analysis and multiple logistic regression.
Results: Out of 1,749 ED records reviewed, 484 visits fulfilled study inclusion criteria. Median age was 4.8 years (IQR 2.1-11.1) and 314 (64.9%) were male. Seventy one (14.7%) patients developed biphasic reactions. Among those who had biphasic reactions, 35 (49.3%) the biphasic reaction was treated with epinephrine. We found five independent predictors of biphasic reaction: age 6-9 years (OR 3.60; 95%CI 1.5-8.58), time from onset of the anaphylactic reaction to ED presentation >90 minutes (OR 2.58; 95%CI 1.47-4.53), wide pulse pressure at triage* (OR 2.92; 95%CI 1.69-5.04), treatment of the reaction with >1 dose of epinephrine (OR 2.7; 95%CI 1.12-6.55), and administration of inhaled Salbutamol in ED (OR 2.39; 95%CI 1.24-4.62).
Conclusions: Biphasic reactions seem to be associated with more severe anaphylactic reactions. We identified five clinical predictors that could ultimately be used to identify patients who would benefit from prolong ED or inpatient monitoring. In agreement with previous literature, we found no benefit of systemic steroids in preventing biphasic reactions. These findings may enable better utilization of ED resources and counseling of patients and families after anaphylactic reactions.