And that improvement occurred at a time when patients who were undergoing surgery were, in general terms, sicker, and the surgeries increasingly more complex.
The lead author of the study said a variety of factors have contributed to the improvement in surgical survival.
"You can't point to one thing," said Dr. Daniel Bainbridge, an anesthesiologist and associate professor in the department of anesthesiology and peri-operative medicine at the University of Western Ontario.
"I'm sure it's better drugs. It's better training of our residents. It's better operating room environments, cleaner environments. Better equipment. It's an understanding about safety and culture safety and avoiding drug errors."
The study, published in this week's issue of the journal The Lancet, was undertaken to see whether advances in the science of anesthetizing people and improved surgical safety procedures were actually translating into fewer deaths in operating rooms.
With more than 230 million major surgeries occurring annually around the world, the stakes are high.
Bainbridge and his group explored the issue by amalgamating data from 87 studies other researchers had done to try to get a global picture of what had been happening over the past few decades to rates of deaths during or immediately after surgery.
The patient pool in the combined studies represents 21.4 million times people were administered general anesthetic for surgery.
Prior to 1970, 357 people per million surgeries died from receiving anesthetic, according to the study. That dropped to 34 people per million in the 1990s and 2000s. Deaths solely due to anesthesia can be caused by allergic reactions to the drugs or by errors on the part of the doctors administering them.
In terms of deaths during or in the day or two after surgery, before the 1970s, 10,603 people died out of every million surgeries. But by the 1990s and 2000s, deaths during or within 24 to 48 hours of surgery dropped to 1,176 people per million worldwide, the research suggested.
There have been high profile steps taken in recent years to improve the safety record of surgeries, such as the adoption of the safe surgery checklist.
The checklist, which was inspired by a similar and successful safety initiative instituted by the airline industry, standardizes safety checks that operating room teams should make before, during and after every surgery.
But interestingly, this study shows that survival rates began improving before the surgical checklist was designed. "Although we're still improving, we've been improving for 20 or 30 years," Bainbridge said in an interview.
A commentary published with the study issued a note of caution. Before surgical teams become complacent, the authors suggested, they should keep in mind that the followup period was short — two days or less. If the studies Bainbridge and his colleagues pooled had looked at deaths a month out from surgery, for example, the picture might have looked different.
"We know from large epidemiological studies that 30-day all-cause perioperative mortality for patients undergoing a broad range of in-patient surgeries remains between one per cent and two per cent," wrote Michael Avidan and Sachin Kheterpal.
That compares to a rate of 0.12 per cent in the 1990s and 2000s in the Bainbridge study.
Avidan and Kheterpal — who are with, respectively, the anesthesiology departments of the medical schools of Washington University in St. Louis, Mo. and the University of Michigan, at Ann Arbor — said it could be that some deaths that are the result of surgeries are now simply happening further out from the procedure.
"There probably remains an unexpected and poorly measured pandemic of perioperative mortality, which is an unappreciated public health concern," they suggested.
But the way the Bainbridge team did this work — collating data gathered by other researchers — means they can only work with the data those studies contained.
And following surgical patients for longer periods becomes complex, Bainbridge admitted. If a patient who had surgery develops pneumonia from the hospital stay and dies six weeks later, is that a surgical death? A hospital-acquired infection death?
The farther out you go, the harder it is to tease out which deaths were due to surgery and which were due to the health status of the person who had the procedure or some mistake in post-operative care.
"Twenty-four to 48 hours (followup) will give you a pretty good idea whether you had a catastrophic event in the OR that would have been caused by anesthesia, surgery or a combination," Bainbridge said.
While the findings of the study are good news, the picture is more favourable in some parts of the worlds than it is in others.
The declines in deaths were greatest and most consistent in developed countries, Bainbridge and his team found. In fact, rates of deaths due to anesthesia or other surgical complications were two to three times higher in developing countries than in developed nations.
The paper suggested the surgical community worldwide should work to close that gap, either through training programs or donations of operating room equipment such as pulse oximeters, which monitor the oxygen levels in a patient's blood.
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