Biphasic anaphylactic reactions: occurrence and mortality

Background: Monitoring after complete resolution of anaphylactic reactions is recommended. The aim of this study was to define the occurrence of biphasic - and clinically important biphasic - anaphylactic reactions, the number of transfers to intensive care units (ICU) because of anaphylaxis, and the number of deaths within 10 days of presentation to the emergency department (ED).

Methods: Clinical records of patients visiting the ED of a tertiary care hospital were analysed retrospectively. Hospital databases, direct contact with patients and caregivers, and the Internet were used to obtain mortality rates.

Results: Of 259 557 ED presentations from February 2001 through to August 2013, 1334 (0.51%) episodes of allergic reactions were detected, and 532 (0.20%) episodes in 495 patients fulfilled the definition of anaphylaxis. In 227 (44.8%) episodes, the length of hospital stay was ≥8 h (median 22 h, IQR 16-24). There were 507 uniphasic and 25 (4.5%) biphasic anaphylactic reactions. Twelve (2.3%) were clinically important, including 2 (0.36%) that occurred during hospital stay, one of whom (0.19%) was transferred to ICU for shock. No risk factors for biphasic reactions could be found. Eight patients were lost to follow-up. There were no deaths during the 10-day follow-up.

Conclusion: Biphasic anaphylactic reactions, especially clinically important ones, occurred rarely, and no mortality was found, whether the monitoring was for ≥8 h or for <8 h. Our study could motivate physicians to consider discharging patients after complete resolution of an anaphylactic reaction and to dispense with prolonged monitoring.