A new study examined whether survival outcomes after out-of-hospital cardiac arrest (OHCA) differ between daytime and nighttime and to what extent these differences may be explained by patient or emergency care factors. Using data from the Cardiac Arrest Registry to Enhance Survival (CARES), the authors analysed adult OHCA cases from 2013 to 2024 to reassess a previously observed survival disadvantage at night and explore potential mediating mechanisms.
The study included 874,415 adult patients. The median age was 64 years, and approximately 64% were male. Most arrests occurred at home (83.2%), and the majority were presumed cardiac in origin (82.2%). Nighttime cases, defined as those with emergency dispatch between 11:00 PM and 6:59 AM, accounted for 27.7% of all arrests.
The primary outcomes were sustained return of spontaneous circulation (ROSC) and neurologically favourable survival at discharge, defined as a Cerebral Performance Category (CPC) score of 1 or 2. The authors compared outcomes between daytime (7:00 AM to 10:59 PM) and nighttime events.
The results demonstrated a consistent and significant survival disadvantage at nighttime. Sustained ROSC occurred in 25.8% of nighttime cases compared with 30.6% during the day. Similarly, neurologically favourable survival was lower at night (6.7% vs 9.3%). These findings indicate that patients experiencing OHCA at night had approximately 14–15% lower adjusted odds of favourable outcomes.
This disadvantage persisted even among patients who achieved ROSC. In this subgroup, post-resuscitation survival remained lower at nighttime, suggesting that differences extend beyond the initial resuscitation phase and may involve postarrest care.
The authors also assessed whether these disparities have changed over time. Risk-adjusted analyses across individual years showed that the survival gap between day and night remained stable from 2013 to 2024, with no statistically significant interaction between year and time of day. This indicates that, despite overall improvements in OHCA survival, the nighttime disadvantage has not narrowed over the past decade.
Subgroup analyses reinforced the robustness of these findings. Among patients with bystander-witnessed arrests and initially shockable rhythms, nighttime outcomes were still significantly worse. Similarly, in arrests witnessed by emergency responders, survival remained lower at night. These results suggest that patient-related physiological differences alone do not explain the observed disparity.
To investigate potential mechanisms, the authors performed a mediation analysis focusing on prehospital response interval, a modifiable system-level factor. Nighttime cases had longer response times (median 7.0 minutes vs 6.2 minutes during the day). The analysis showed that response interval mediated approximately 12.6% of the total effect of nighttime on survival. While statistically significant, this modest proportion indicates that most of the survival disadvantage is attributable to other, unmeasured factors.
The discussion highlights several plausible explanations for the persistent nighttime disadvantage. These include differences in bystander recognition and response, such as delayed identification of cardiac arrest or lower-quality cardiopulmonary resuscitation (CPR) due to fatigue or reduced vigilance at night. Additionally, inaccuracies in estimating arrest timing may be more common during sleep hours. Prehospital care factors beyond response time, such as access to automated external defibrillators (AEDs), timing of epinephrine administration, and CPR quality, may also vary by time of day but were not fully captured in the dataset.
The study also raises the possibility that hospital-based factors contribute to poorer nighttime outcomes. Among patients who achieved ROSC, survival to discharge with favourable neurological status was lower at night, potentially reflecting reduced staffing, limited access to advanced therapies, or variability in postarrest care practices during overnight hours.
Overall, this study confirms that OHCA occurring at night is associated with significantly lower odds of sustained ROSC, neurologically favourable survival, and post-resuscitation survival compared with daytime events. This disparity has persisted for over a decade and is only partially explained by longer emergency response times. The findings suggest that additional factors, likely related to both prehospital and in-hospital care, contribute to poorer nighttime outcomes. The authors emphasise the need for further research to identify modifiable system-level interventions that could reduce this disparity and improve survival for patients experiencing cardiac arrest at night.
Source: JAMA
Image Credit: iStock
