Out-of-Hospital Cardiac Arrest Survival at Nighttime: A Nationwide Cohort Study

Studies have demonstrated lower odds of survival from out-of-hospital cardiac arrest (OHCA) during nighttime hours, but this has not been studied in North America since 2013, and it is unclear what factors might explain this survival difference.

To identify whether OHCA survival during nighttime hours remains lower than during daytime hours using contemporary data and whether it can be explained by variable patient physiology or emergency care factors.

This cohort study included adults (aged ≥18 years) with OHCA in the Cardiac Arrest Registry for Enhanced Survival from 2013 to 2024.

Daytime was defined as 7:00 am to 10:59 pm, and nighttime was defined as 11:00 pm to 6:59 am.

Primary outcomes were sustained return of spontaneous circulation (ROSC) and neurologically favorable survival (Cerebral Performance Category score of 2 or more). A multilevel mixed-effects logistic regression model with prehospital agency as a random effect and patient or treatment characteristics as fixed effects was used. A similar analysis of postresuscitation survival was performed among patients with sustained ROSC, adjusting for the time-to-cardiopulmonary resuscitation interval and defibrillation status. A mediation analysis was performed to identify whether the prehospital response interval mediates the association.

Of 1 151 845 patients in the registry, 874 415 were eligible and included in the analysis, and the median (IQR) age in the cohort was 64 (52-75) years with 557 515 males (63.8%) and 181 878 Black or African American patients (20.8%), 146 352 Hispanic or Latino patients (16.7%), and 447 646 White patients (51.2%). A minority of OHCA responses occurred at nighttime (241 967 [27.7%]), and the odds of sustained ROSC and neurologically favorable survival were lower at nighttime than daytime (sustained ROSC: 62 548 [25.8%] vs 193 486 [30.6%]; adjusted odds ratio [aOR], 0.85; 95% CI, 0.84-0.86; neurologically favorable survival: 16 234 [6.7%] vs 58 542 [9.3%]; aOR, 0.84; 95% CI, 0.82-0.86). Among those with sustained ROSC, the odds of postresuscitation survival at nighttime were also lower than daytime (aOR, 0.93; 95% CI, 0.90-0.95). The prehospital response interval partially mediated the nighttime survival disadvantage, with approximately 12.6% of the total effect mediated by the response interval.

In this cohort study of OHCA, nighttime response was associated with lower adjusted odds of sustained ROSC, neurologically favorable survival, and postresuscitation survival. Emergency care factors accounted for only a portion of the decreased odds of survival at nighttime.