Biphasic anaphylactic reactions: occurrence and mortality

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).

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.

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.

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.