Riskiest time for non-cardiac surgery patients is after they leave the operating room

Canadian-led research identifies bleeding, injury to heart muscle and septic infection as main causes of post-operative death.

Non-cardiac surgery patients are at most risk for serious complications and death during the days and weeks after their surgery, not when they are on the operating table, according to new research published in the Canadian Medical Association Journal.

Researchers from around the world, including the University of Alberta, followed 40,000 patients in 14 countries for a month after surgery. They found that 715 people died in that time. Of those, only five died during surgery, 500 died in hospital and 210 died after being sent home.

Bleeding, heart damage and severe infection were responsible for nearly 45 per cent of the deaths, leading the researchers to recommend better prevention, early identification and management of these three complications.

Though researchers knew that surgery patients are generally older and sicker than in previous generations, this is the first time such a large study has been done to track the cause of death in non-cardiac surgery patients.

"We came to the realization that we needed a broader database to determine why people were dying after surgery, how frequently it was happening and what was leading to it," said Michael Jacka, associate professor of critical care medicine, anesthesiology and pain medicine at the U of A, and principal investigator for the 2,000 participating patients at the University of Alberta Hospital.

"We wanted it to be large enough that we could use population-based statistics to determine attributable risk with confidence," he explained.

The patients were 45 years or older and had at least one risk factor such as diabetes, high blood pressure or kidney trouble, but no current symptoms of heart disease. They stayed in the hospital for at least one night and an average of four nights. They underwent a range of surgeries including orthopedic, vascular, gynecological and joint replacement between 2007 and 2011. Ten per cent had emergency surgeries.

Jacka said surgery can be likened to an extreme cardiac stress test on a treadmill, in which changes to blood pressure, oxygen levels and the release of hormones can lead to blood clots in the brain and heart.

Risk assessment tools

The same research team developed a number of risk assessment tools to predict which surgery patients might face deadly complications, including a preoperative lab test for a hormone called brain natriuretic peptide (BNP), which is produced when the heart muscle is damaged, even without symptoms, and a post-operative test for the chemical troponin, another sign of heart injury.

Jacka said those with elevated levels should receive more intensive post-operative monitoring of their blood pressure and other vital signs to ensure they avoid further heart damage.

He added that next steps for the research team include testing the effectiveness of a medication called tranexamic acid to optimize clotting after surgery, and an investigation into the link between permanent cognitive damage and post-operative delirium.

The research team estimates that 100 million people over age 45 undergo non-cardiac surgery each year. While surgery has the potential to improve and save lives, and surgical techniques have improved, Jacka said the research will help patients understand the risks of undergoing surgery.

"You want to be sure your doctors and nurses are operating with the best information, giving you the best information, from which you can make your own decisions," he said. "You don't want to rely on guesswork."

The research was funded by the Canadian Institutes of Health Research and the Population Health Research Institute.