Invited Commentary 

Emergency Medicine

Is Poor Recognition of Out-of-Hospital Cardiac Arrest to Blame for Worse Rates of Survival at Night?

Sarah M. Perman

JAMA Netw Open 2026;9;(4):e269837.

doi:10.1001/jamanetworkopen.2026.9837

Emergency care is a 24 hours-a-day, 7 days-a-week, and 365 days-a-year operation. Those of us in emergency medicine, prehospital medicine, and acute critical care staff departments and agencies care for any patient with any condition any day of the week, any hour of the day, through blizzards, hurricanes, and pandemics. To that end, there is reason for alarm when differences in outcomes are compared between nighttime and daytime, given that emergencies can happen at any time of day. In this article entitled “Out-of-Hospital Cardiac Arrest Survival at Nighttime” by Kimbrell et al,¹ the authors conducted a secondary analysis of the Cardiac Arrest Registry to Enhance Survival (CARES) dataset to explore achievement of return of spontaneous circulation and neurologically intact survival after resuscitation at night (11:00 pm to 6:59 am) vs day (7:00 am to 10:59 pm). The authors determined that fewer of the resuscitation events in the registry occurred during the 8 nighttime hours (27.7%) and that both primary outcomes were worse for persons who arrested at night compared with day (sustained ROSC: aOR, 0.85; 95% CI, 0.84-0.86; neurologically favorable survival: aOR, 0.84; 95% CI, 0.82-0.86).¹ The authors corroborate previous findings on this topic, which have found differences in survivability by time of day, including 2 large meta-analyses looking at outcomes after OHCA.^2,3 Even when accounting for patient and event characteristics and prehospital interventions, differences in outcomes persisted. Kimbrell et al¹ presented 2 additional analyses—first, a sensitivity analysis to explore differences in ROSC and neurological survival in individuals with OHCA with witnessed OHCA due to shockable rhythms and second, a mediation analysis to explore the role of EMS response time on outcomes. Despite these subanalyses, nighttime outcomes remain worse. Given these additional analyses to augment the primary study question, one must ask: what is the driver of differences in outcome between night and day? Are there unmeasured factors that contribute to these differences, or potential patient characteristics, such as diurnal variability, that predispose nighttime arrests to being more devastating? Or maybe there is a third reason that seems too obvious to be true—is it possible that our measure of a bystander witnessed arrest at night is inherently different than during the day? These multiple analyses include an unmeasured factor: our poor recognition of OHCA during nighttime hours, which results in prolonged downtimes and worse neurologic recovery.

In cardiac arrest outcomes research, we have identified factors that contribute to improved outcomes, including witnessed arrest, bystander cardiopulmonary resuscitation (CPR), and early deployment of automated external defibrillation. These measures are abstracted and recorded from prehospital run sheets and cardiac arrest code sheets into registries, such as CARES or Get With the Guidelines (GWTG). Data dictionaries exist to ensure that these data elements are abstracted uniformly. CARES defines witnessed arrest as “one that is seen or heard by another person.”⁴ This seems a natural measure when, for example, your tennis partner collapses on the court or your spouse becomes unconscious at the dinner table. But how is this defined during nighttime hours when patients and their cohabitants are asleep? Is it the first time someone in the home awakens and realizes that the individual is not breathing right, or is it when a member of the household checks on another member to find them in some state of extremis? Those of us who work in emergency and prehospital medicine have heard these stories frequently, where abnormal sounds (irregular snoring or gasping) or movements have woken others, but is this a true witnessed arrest? Are they truly witnessing the time of arrest at night, or could their recognition of the actual arrest event be delayed, and we are just capturing when the event was noticed? To that end, I suggest that a potential driver to worse outcomes at night is not the time from when EMS is dispatched to when they arrive on scene, nor is it the notion that maybe our resuscitations aren’t as sharp, but 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. To further this point, Kimbrall et al¹ presented a forest plot indicating worse outcomes between 1:00 am and 5:00 am, which I might suggest is when even night owls are prone to rest. To summarize, could outcomes be worse at night due to delayed recognition of the arrest event? And is it possible that a variable like witnessed arrest could be prone to inaccuracies when measured during nighttime hours?

This study reinforces prior literature^2,3 that has identified nighttime as a very vulnerable time for patients with OHCA, and Kimbrell et al¹ included additional sensitivity and mediation analyses that failed to isolate the reason for the differences measured. These differences may be attributed to delayed recognition of cardiac arrest at night, and the usual measure of witnessed arrest may be a flawed estimation of recognition of arrest. There is a growing cohort of scientists and engineers dedicated to early recognition of cardiac arrest. Technological interventions, such as wearable devices that monitor heart rates and rhythms or training artificial intelligence (AI) assistants to detect irregular respirations, may one day provide the added resource of early detection that is necessary^5,6 and be especially useful during nighttime hours. The phenomenon recognized in nighttime cardiac arrest might even be compared with Sudden Infant Death Syndrome, another devastating event similar to cardiac arrest where more than of 80% of deaths occur between 12:00 am and 6:00 am.⁷ Clearly, outcomes are poor, and major contributing factors, such as immature central nervous systems leading to poor arousal mechanisms, are higher during nighttime sleep; the high prevalence of nighttime SIDS deaths goes unrecognized until morning. Again, a devastating disease with poor outcomes that is most likely driven by recognition challenges at nighttime and not necessarily a commentary on the provision of care or response at night vs day.

Is OHCA at night vs the day different? Probably not. Do we resuscitate OHCA at night differently than during the day? I would also argue, probably not, given how we have designed our emergency care systems to be 24 hours a day, 7 days a week, and 365 days a year. But is it possible that our recognition at night is different than during the day? I think so. One unmeasured factor that has not been integrated into the numerous analyses of outcomes difference in rates of ROSC and neurologic recovery, is how delayed we are in recognizing nighttime arrest, and is our categorization of a witnessed event a gross underestimation of the duration of physiologic low- or no-flow states. While we cannot advocate for telemetry and pulse oximetry monitors in every private household, it is possible that the role for advanced technologies, such as wearable smart watches and smart speakers, might raise nighttime recognition of OHCA in higher risk patients and result in more rapid response from household members to alert emergency services. This could result in more rapid responses and improved outcomes.