Biphasic anaphylactic reactions in pediatrics

Objectives. The objectives of this study were to: 1) determine the incidenc e of biphasic reactions in children with anaphylaxis; 2) establish what ris k factors can predict progression to a biphasic reaction; and 3) assess the utility of inpatient observation for patients whose anaphylaxis appears to have resolved. Methods. We performed a retrospective analysis of all children admitted to Children's Hospital inpatient service between 1985 and 1999 with acute anap hylaxis. Data were collected from the medical records regarding past medica l history, presenting signs and symptoms, treatment, and hospital course. P atients were considered to have resolution of anaphylaxis if they were docu mented to have cessation of all symptoms and needed no therapy for at least 1 hour. Biphasic reactions were defined as a worsening of symptoms requiri ng new therapy after resolution of anaphylaxis. Significant biphasic reacti ons were defined as those requiring oxygen, vasopressors, intubation, subcu taneous epinephrine, or unscheduled bronchodilator treatments. Patients wer e considered to benefit from a 24-hour observation period if they had a sig nificant biphasic reaction within 24 hours of admission. Results. Of 108 anaphylactic episodes, 2 (2%) were fatal, and 1 (1%) was a protracted anaphylactic reaction. Among the remaining 105 children with res olution of anaphylaxis, 6 (6%) [95% confidence (CI): 2, 12] had biphasic re actions, of which 3 (3%) [95% CI: .6, 8] were significant. Of those who had a biphasic reactions, the median time from the onset of symptoms to the in itial administration of subcutaneous epinephrine was 190 minutes, versus 48 minutes for those without a biphasic reaction. Patients with or without bi phasic reactions did not differ significantly in the incidence of initial e pinephrine use, initial steroid use, or serious respiratory or cardiovascul ar symptoms on initial presentation. Two of 105 (2%) [95% CI: .2, 7] patien ts clinically benefitted from a 24-hour observation period. Conclusions. We found an overall incidence of biphasic reactions of 6%, and an incidence of significant biphasic reactions of 3%, among pediatric pati ents admitted with anaphylaxis. Delayed administration of subcutaneous epin ephrine was associated with an increased incidence of biphasic reactions. A pproximately 2% of patients with anaphylaxis potentially benefitted from a 24-hour period of observation after symptoms had resolved.