Pediatric Anaphylaxis in a Tertiary Pediatric Emergency Department: Observation Duration and Biphasic Reactions

Background/Objectives: Biphasic reactions are an important consideration during post-treatment observation of children with anaphylaxis; however, real-world pediatric data on observation practices and the timing of these reactions remain limited. This study aimed to describe the clinical characteristics, management practices, observation duration, and occurrence of biphasic reactions among children presenting with anaphylaxis to a tertiary pediatric emergency department (PED). Methods: This single-center retrospective observational study included children aged 0-18 years who presented with anaphylaxis to a tertiary PED between January 2014 and December 2024. Potential cases identified through ICD-10 codes and PED intramuscular adrenaline administration records were reviewed to confirm the diagnosis according to established criteria. Demographic and clinical characteristics, suspected triggers, treatments, observation duration, and biphasic reactions were evaluated. Results: Seventy anaphylaxis episodes in 68 patients were analyzed. The median age was 93.5 months (IQR, 50-156). Food (32.9%) and insect stings (28.6%) were the most common suspected triggers, followed by drug/vaccine-related triggers (18.6%) and allergen immunotherapy (11.4%). Adrenaline was administered in 94.3% of episodes, and intravenous fluid therapy in 50.0%. Central nervous system involvement and age-adjusted hypotension were more frequent among episodes receiving intravenous fluid therapy (p = 0.004 and p < 0.001, respectively). The median PED observation duration was 5.5 h (IQR, 2-8). Biphasic reactions occurred in three episodes (4.3%), all within three hours after initial symptom resolution. Conclusions: In this tertiary PED cohort, adrenaline administration was frequent, and biphasic reactions were uncommon and occurred during the early observation period. Given the small number of biphasic reactions, these findings should be interpreted as descriptive and are insufficient to determine the optimal observation duration.