The timing of surgical procedures—afternoon versus morning or Friday versus Monday—doesn't affect the risk of death after surgery, concludes a study in the December issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society.

The findings help to alleviate concerns that fatigue may contribute to an increased rate of safety problems for operations performed later in the workday or workweek. The study also shows no increase in mortality in the summer months, when new residents begin work.

Led by Dr. Daniel I. Sessler of The Cleveland Clinic, the researchers analyzed the outcomes of 32,001 elective surgeries performed from 2005 to 2010. The risk of death within 30 days after surgery was analyzed according to time of day of the procedure (from 6 a.m. to 7 p.m.), day of the week, and month of the year.

The researchers took steps to eliminate emergency surgical procedures from the study, along with certain types of surgeries that are performed commonly on an urgent basis. As a negative control, differences in outcome by phase of the moon were analyzed as well.

The overall risk of death within 30 days after surgery was 0.43 percent. After adjustment for other factors, mortality risk was not significantly different for patients operated on at different times of day. Neither was there any evidence of an increased risk of death for operations performed later in the workweek.

There was also no difference in mortality by time of year. Specifically, risk didn't increase for operations performed in July and August, which is when most new residents start working in teaching hospitals.

As expected, there was no difference by phase of the moon.

A similar analysis found no difference in complication rates for surgeries performed at different times of the day, days of the week, or months of the year. The overall rate of in-hospital complications was 13 percent.

"Human factors such as fatigue, circadian rhythms, scheduling, and staffing may have an impact on patient care across medical specialties," the study says. Some previous studies have raised concerns of a decline in safety for operations performed later in the day.

The findings have important implications for operating room scheduling, according to an accompanying editorial by Drs. Franklin Dexter and Alan P. Marco. The results suggest that facilities can decide whether to add additional operating rooms or run the scheduled operating rooms late on busy days based entirely on the economic tradeoffs, because patient safety is not compromised either way.