Out of Hospital Cardiac Arrest Survival: Why Time Matters
A recent study published in JAMA Network Open examined an important question in emergency medicine: Does the time of day when an out-of-hospital cardiac arrest (OHCA) occurs affect a patient’s chances of survival? Researchers found that cardiac arrests receiving a prehospital response at night were associated with significantly lower odds of survival and favorable neurological outcomes compared with those occurring during the day.
The nationwide cohort study analyzed data from 874,415 patients with out-of-hospital cardiac arrest between 2013 and 2024 using information from the Cardiac Arrest Registry to Enhance Survival (CARES). Nighttime was defined as 11:00 p.m. through 6:59 a.m., while daytime included 7:00 a.m. through 10:59 p.m. The researchers found that patients experiencing cardiac arrest at night had 15% lower adjusted odds of neurologically favorable survival and 14% lower adjusted odds of achieving a sustained return of spontaneous circulation (ROSC).
The differences were particularly notable among patients whose cardiac arrest was witnessed by a bystander and who initially had a shockable heart rhythm. In this group, nighttime cardiac arrests were associated with even lower odds of both sustained ROSC and neurologically favorable survival. The study also found that nighttime responses had longer median response intervals of 7.0 minutes compared with 6.2 minutes during the day, as well as longer times to CPR and defibrillation.
Several factors may help explain these differences. At night, cardiac arrests are more likely to occur in residential settings, where immediate recognition and intervention can be more difficult. In the study, nearly 89% of nighttime cardiac arrests occurred at home or in a residence, compared with 81% during the daytime. Nighttime cases were also less likely to be witnessed by a bystander and less likely to involve the application of a public automated external defibrillator (AED).
These findings reinforce a fundamental principle of cardiac arrest care: every minute matters. Rapid recognition, immediate CPR, early defibrillation, and timely emergency medical services can all play a critical role in determining whether a patient survives and, importantly, what their neurological recovery looks like.
For healthcare organizations, the study also demonstrates the value of collecting and analyzing detailed clinical data. Looking beyond overall survival rates can help identify patterns that may otherwise be missed. Examining factors such as response times, location, witnessed status, initial rhythm, CPR, defibrillation, and time of day provides a more complete picture of where opportunities for improvement may exist. The study’s findings serve as another reminder that healthcare quality is not simply about treating patients when they arrive at the hospital. It encompasses the entire continuum of care, beginning with recognition of an emergency and continuing through treatment, resuscitation, and recovery.
Understanding why outcomes differ and using reliable data to identify those differences is an important step toward improving care. As researchers continue to investigate strategies for improving nighttime cardiac arrest survival, healthcare organizations can use data-driven insights like these to better understand their own performance and work toward stronger outcomes for patients, regardless of when an emergency occurs.
