Incidence, predictors, and treatment outcomes of biphasic anaphylaxis in the emergency department of a tertiary hospital:A 5-year retrospective study.

Background: Biphasic anaphylaxis despite successful treatment has an incidence of 4-5% based on NIAID/FAAN criteria. Our study aimed to investigate the frequency and predictive factors associated with biphasic reactions within the emergency department (ED) at Siriraj Hospital.

Methods: This observational study assessed medical records of anaphylaxis and anaphylactic shock patients at Siriraj Hospital's ED from January 2015 to December 2019. Of these, a random sample was reviewed and validated by allergists. Telephone interviews were performed to collect more data. Uni- or biphasic response were analyzed descriptively. Prediction modeling was performed.

Results: Among 1888 ED anaphylaxis cases, 601 were randomly sampled; 239 patients completing interviews were analyzed. The incidence of biphasic reactions was 7.1% (17/239) of cases. Common triggers of biphasic responses were foods (57.7%), drugs (31%), other known allergens (5.9%). Shellfish, edible insects, and wheat were the leading food triggers. Biphasic responses were significantly associated with history of drug allergy, any allergic disease, allergic rhinitis, number of prior anaphylactic reactions, angioedema, less generalized erythema, less reaction to shellfish, reaction to NSAIDs, and no epinephrine giving at ED visit (all p < 0.1). From a 3-predictor prognostic model including drug/idiopathic reaction, duration from onset to first epinephrine > 60 minutes, and any cutaneous edema/angioedema with an area under the curve of 0.72 (95%CI 0.54, 0.90).

Conclusion: The incidence of biphasic response was 7.1%. Predictors of biphasic response were drug/idiopathic reac- tion, any cutaneous edema/angioedema, and time from onset to first epinephrine > 60 minutes.