Going without sleep the night before does not affect the performance of doctors doing elective surgery the next morning, according to a new Ontario study that runs contrary to research demonstrating that sleep-deprived physicians pose a hazard to patients.

The odds of having a surgery-related problem were 22.2 percent when the doctor had been treating patients between midnight and 7 a.m. and 22.4 percent when the doctor had, presumably, received sufficient sleep.

The senior author of the study, Dr. Nancy Baxter of the University of Toronto, told Reuters Health in a telephone interview that the new results argue against proposals calling for doctors to inform their patients if they are sleep-deprived.

But the study didn't directly measure how much sleep the doctors actually received, said Dr. Charles Czeisler, chief of the division of sleep and circadian disorders at Brigham and Women's Hospital in Boston. He was not connected with the research.

According a 2009 study that he and his colleagues published in the Journal of the American Medical Association (JAMA), once the actual amount of sleep is taken into consideration, the odds of a serious mistake nearly triple.

"Given the increased risk that we've seen with just one night of insufficient sleep, patients have the right to know if their doctor has been awake for one night, two nights, or even three consecutive nights," he told Reuters Health by phone.

The Baxter study, released Wednesday in The New England Journal of Medicine, was based on data from 147 hospitals in Ontario. It looked at nearly 39,000 cases performed by 1,448 experienced surgeons.

The researchers tracked 12 widely-varying types of operations, from bypass surgery and hip replacement to hysterectomy and angioplasty, done during a five-year period. A billing code database told them whether the doctor had worked from midnight to 7 a.m. the night before the operation.

Thirty days after surgery, the odds of death were 1.1 percent whether or not the doctor had worked during the early morning hours before the operation. The readmission rates were 6.6 percent if the surgeon had been up late and 7.1 percent if he or she had not. The 30-day complication rate was 18.1 percent in the overnight group and 18.2 percent when overnight work was not a factor. In both groups, half the patients went home in three days or less.

The type of hospital, the doctor's age and the type of operation made no difference.

Czeisler said he and his colleagues reported similar results in their 2009 study of 4,471 cases, which is online here: bit.ly/1NBkEkv.

But simply looking at whether a doctor did any work overnight doesn't tell you if the physician was actually sleep deprived, he said. For example, an hour-long procedure might be done at midnight and the doctor may not have to be back at work until late the next morning.

So in their JAMA study, the Czeisler team went further. They calculated the actual time between the overnight procedure and the morning procedure.

When the doctor had only six hours or less to sleep, the complication rate was 170 percent higher than when the doctor had the opportunity to sleep more than six hours.

He said the Baxter study didn't go far enough because, "If you don't know if the person is sleep deprived, you can't evaluate it."

He also faulted the study for assuming that doctors who worked anytime from midnight to 7 a.m. hadn't received a full night's sleep. Surgeons often start their day before seven.

"Physicians who have started their procedure at 6:30 in the morning would be placed in that sleep-deprived group" when they probably don't belong there, Dr. Czeisler said.

Baxter, in a follow-up email, acknowledged that "we do not know how much sleep was lost. However we looked at the subgroup of individuals who performed at least two procedures overnight, assuming they were up for most of the night, and still did not see a consistent signal - certainly nothing like the effect found by the JAMA study."

"The JAMA study was in a single institution and included only a small number of patients and providers. It is possible that the findings were due to chance alone," she said. Alternatively, the doctors in the JAMA study might not have had the flexibility to changes their schedules to avoid sleep deprivation.

Baxter, who is chief of the division of general surgery at St. Michael's Hospital in Toronto, said lack of sleep may not have had an effect because experienced surgeons know how to pace themselves, their experience lets them do an adequate job even when they're tired, and "surgeons tend to be people who deal better with lack of sleep than other physicians" thanks to self-selection.

But the findings should not be considered by doctors to be a license to work without proper rest, she said. "I don't want people to take from this the idea that this is open season on being on call and operating the next day without self-regulation being in place, without understanding your abilities, and potentially canceling cases if you're that tired," she said.

As for patients who might be concerned if their surgeon was up the night before, Baxter said. "It's probably something they don't need to worry about."

Said Czeisler: "They're talking about sleep deprivation without having determined if these doctors were sleep deprived."