This nationwide study examined whether survival after out-of-hospital cardiac arrest (OHCA) is worse when emergency response occurs at night compared with daytime. Using data from over 874,000 adult cardiac arrests in the U.S. Cardiac Arrest Registry for Enhanced Survival (2013–2024), researchers compared outcomes between nighttime (11:00 pm–6:59 am) and daytime (7:00 am–10:59 pm) events, focusing on return of spontaneous circulation (ROSC) and neurologically favorable survival.
The study found that nighttime cardiac arrests were consistently associated with worse outcomes. Patients who experienced OHCA at night had lower odds of both ROSC (about 26% vs 31% during the day) and neurologically favorable survival (about 6.7% vs 9.3%).
The authors suggest that important factors likely contribute to these differences, particularly related to early bystander response. One key consideration is the quality and timing of bystander recognition and CPR before emergency responders arrive. The CARES registry defines a “witnessed arrest” as one that is seen or heard by a bystander—for example, a family member who wakes up after hearing abnormal breathing and finds the person unresponsive. However, even when an arrest is classified as witnessed, recognition and initiation of chest compressions may be delayed or less effective at night due to sleep, fatigue, or confusion. In addition, key data points such as estimated time of arrest may be harder for bystanders to accurately report during nighttime events. These factors suggest that differences in early recognition and response may help explain why survival is lower at night.
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SOURCE: JAMA