A new University of Pennsylvania study shows that CPR administered at night is less effective than CPR performed during the day. Researchers say lower staffing levels, fatigue, and slower responses times are to blame.

According to the study, nurses and doctors administer CPR compressions more slowly at night. In some cases, the rate of compressions dropped to levels that could put the cardiac patients at risk of oxygen deprivation to the brain.

Dr. Benjamin Abella, senior author of the study and clinical research director at Penn’s Center for Resuscitation Science, said the study could explain why survival rates for cardiac arrest are lower at night.  

"At night, the self-assembly of teams in the hospital in rapid fashion is difficult,” Abella said. “And in addition, a lot of the attention to detail, the precision of care can be more problematic at night."

Abella said the same problems infringe on night-time responses to all kinds of emergencies in hospitals. But because cardiac arrest requires a rapid response and coordinated team effort, there's a smaller margin for error than in treating most other conditions.

Jackie Yates was a night-time nurse at Penn Presbyterian for about 14 years before she switched to days. She says there are fewer nurses on the floor at night, but there aren't necessarily fewer emergencies to attend to.

"You know, it's not like they can take off Christmas,” Yates said. “The patient comes in and he's sick. It can be busy the whole 24/7."