Morning may be the safest starting time for surgery, according to a new study.

Researchers found patients anesthetized for surgery in the afternoon were much more likely to develop anesthesia-related complications than those whose surgeries began in the morning.

"This is one of the first studies to show that there is a difference in patient outcomes depending on the start time of surgery," says researcher Melanie Wright, a human factors specialist at the Duke University Human Simulation and Patient Safety Center, in a news release.

"We found that adverse events (or problems) were most common for operations starting between 3 p.m. and 4 p.m.," says Wright. "Furthermore, the predicted probability of an adverse event in the "other" category increased from a low of 1% at 9 a.m. to a high of 4.2% at 4 p.m."

Researchers say only a very small percentage of the anesthesia-related problems harmed the patient. The majority involved serious, but not life-threatening, difficulties with pain management or nausea and vomiting after surgery.

Obesity May Make Anesthesia Riskier

Surgery Start Times May Matter

In the study, published in Quality and Safety in Health Care, researchers compared the risk of complications related to anesthesia in more than 90,000 surgeries performed at Duke University Medical Center from 2000 to 2004.

The results showed the likelihood of anesthesia-related problems was lowest in surgeries that started in the morning and highest among those beginning in late afternoon.

Health Care Varies Greatly at U.S. Hospitals

Types of Trouble

Researchers divided the types of problems into three categories: error (including administration of wrong medications or wrong doses); harm (including prolonged sedation, wound infection, and nausea and vomiting after surgery); and “other adverse events,” such as with pain management.

The results showed 31 cases of error, 667 of harm, and 1,995 in the “other” category.

The researchers say about half the complications in the other category were related to management of the patient’s pain, and about a third of the harm events were due to nausea and vomiting after surgery.

In addition to these problems, researchers also identified more than 9,400 cases of administrative delay, which increased significantly in the afternoon and may have contributed to the rise in anesthesia-related problems found at that time.

The delays included waiting for lab test results, doctors running late, staff not being available to transport patients, and rooms not being ready in time.

Where are the Best Hospitals in America?

Hospitals and Patients May Play a Role

Wright says many factors related to both hospitals and their patients may contribute to the increase in anesthesia-related problems in the afternoon.

For example, some patients may be more susceptible to either pain or nausea in the afternoon.

On the hospital staff side, institutional work schedules that interfere with the body’s natural sleep-wake cycle (circadian rhythm), as well as administrative delays, may play a role.

End-of-day fatigue, a circadian low point, and shift changes in caregivers all occur around 3 p.m. to 6 p.m. and may be interacting in a way that affects patient care, says Wright.

"Health care is a 24-hour-a-day business, and it is not unexpected that factors such as fatigue, circadian rhythms, personnel shift changes, and scheduling may affect patient care over the course of a day," Wright said.

"We believe that identifying the specific periods when problems are most likely to occur is an important step in the overall process of making surgery safer and ensuring that patients have a good experience."

By Jennifer Warner, reviewed by Louise Chang, MD

SOURCES: Wright, M. Quality and Safety in Health Care, August 2006; vol 15: pp 258-263. News release, Duke University Medical Center.