According to research from a 5 year study, presented at the World Congress of Anesthesiologists, patients are more likely to die if they undergo a surgical procedure at night.

Researchers, led by Michael Tessler, M.D of Montreal’s McGill University Health Center, found that patients were 2.17 times more likely to die during nighttime surgeries than during daytime procedures.

Those undergoing procedures later in the day 1.43 times more likely to die than those undergoing it during regular daytime hours.

The research analyzed all surgical procedures over a five-year period at Montreal’s Jewish General Hospital. This included an evaluation of surgical outcomes with the work day divided into day, evening and night blocks, with the start time of the anesthetic marking the time the procedure began.

Researchers initially found that among 41,716 elective and emergency procedures, 226 deaths occurred in the day compared to 97 in the evening and 29 at night, similar to the breakdown of procedure performed during the three blocks.

There are numerous potential reasons for the increased risk, according to the researchers.

For example, provider fatigue as the day wears on is a major concern. Treatment is also delayed in some cases due to lack of room availability or patients being too sick to be postponed prior to treatment.

Despite these risks, research indicates providers are increasingly hiring doctors to work overnight shifts.

The authors of the study feel that awareness of these risks is a valuable step towards lowering the risk of death during surgery.  “Analysis of each of these possibilities is important to understand the reasons for this increased mortality and to direct any remedial action in an effort to reduce postoperative mortality.”