Nighttime response for out-of-hospital cardiac arrest (OHCA) was associated with lower odds of sustained return of spontaneous circulation (ROSC), neurologically favorable survival (Cerebral Performance Category of 1 or 2) and postresuscitation survival compared to daytime, even after adjusting for patient and event characteristics and emergency care factors, according to an analysis of 2013-2024 Cardiac Arrest Registry for Enhanced Survival (CARES) data published April 29 in JAMA Network Open.

Of the 874,415 eligible adults (median age, 64; 36% women; 51% White, 21% Black, 17% Hispanic or Latino) identified in the registry, 28% experienced OHCA during the nighttime hours (11 p.m.-6:59 a.m.). Of these, 38% had bystander-witnessed arrests, 82% had suspected cardiac etiology and 83% experienced OHCA at home.

Results showed that OHCA responses during nighttime hours carried lower odds of sustained ROSC (25.8% vs. 30.6%; adjusted odds ratio [aOR], 0.85), neurologically favorable survival (6.7% vs. 9.3%; aOR, 0.84) and postresuscitation survival (aOR, 0.93). Of note, the odds of neurologically favorable survival began to significantly drop as early as 8 p.m. before continuing into the night.

The nighttime disadvantage persisted within subgroups of bystander-witnessed, initially shockable OHCA and 911 responder-witnessed OHCA, and throughout the entire 11 years of the study. Prehospital response time only mediated this by 12.6%.

"Further work should investigate whether AED access, time-to-epinephrine, time-to defibrillation, CPR quality, and other CPR process metrics mediate the disadvantage," suggest study authors Joshua M. Kimbrell, BA, et al. "If [so], then the nighttime survivable disadvantage might be exploited by high-performing prehospital quality improvement leaders and clinicians performing resuscitations."

In an accompanying editorial comment, Sarah M. Perman, MD, MSCE, writes that a potential driver may be "rather as simple as the fact that cardiac arrest at night, when household members are asleep and an individual does not have a dramatic collapse or become acutely unconscious, results in delays in recognition of the arrest event."

"Technological interventions, such as wearable devices that monitor heart rates and rhythms or training artificial intelligence assistants to detect irregular respirations, may one day provide the added resource of early detection that is necessary and be especially useful during nighttime hours," she concludes.