ABSTRACT
Objective@#The characteristics and prognosis of out-of-hospital cardiac arrest (OHCA) patients can vary due to a variety of factors, including the time of the day. We tried to identify the characteristics and prognosis of OHCA in a Korean metro city based on the time of the day. @*Methods@#This citywide retrospective observational study was conducted from January 1, 2015, to November 31, 2020, in Daegu, Korea on patients over 18 years of age who were suspected of having a medical etiology of OHCA. We evaluated the characteristics and outcomes of OHCA, according to the time of day, divided into dawn (00:00-05:59), morning (06:00-11:59), afternoon (12:00-17:59), and night (18:00-23:59). The outcome variables were survival to hospital discharge and favorable neurological outcomes. @*Results@#The median age of the total of 4,783 OHCA patients in the study was 72.0 years of which 3,096 (64.7%) were males. The number of patients who survived was 317 (7.8%) and 301 (6.3%) were discharged with favorable neurological outcomes. There were 672 (14.0%) patients admitted at dawn, 1,607 (33.6%) in the morning, 1,379 (28.8%) in the afternoon, and 1,125 (23.5%) at night. After adjusting for the possible confounding variables, compared with the morning group, the survival to hospital discharge was low in the afternoon and the night (adjusted odds ratio [aOR], 0.69; 95% confidence interval [CI], 0.48-0.98 and aOR, 0.48; 95% CI, 0.32-0.74). In addition, favorable neurological outcomes were also low in the afternoon and the night compared with the morning (aOR, 0.59; 95% CI, 0.40-0.85 and aOR, 0.62; 95% CI, 0.41-0.93). @*Conclusion@#Diurnal differences in OHCA outcomes were observed. Identification of the diurnal OHCA characteristics will be necessary to devise an appropriate regional emergency medical services strategy.