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Older adults who undergo elective surgeries, such as hip or knee replacements, commonly experience “silent” strokes (strokes with no obvious symptoms) that double their risk of cognitive decline a year later, researchers have found.

Cardiologist and co-lead researcher P.J. Devereaux, a senior scientist at the Population Health Research Institute of McMaster University and Hamilton Health Sciences.

The Canadian Press

In a study published in The Lancet on Thursday, an international team led by Canadian researchers found 7 per cent of patients, or one in 14, aged 65 or older had a silent stroke after elective, non-cardiac surgery. These silent strokes, also called covert strokes, can occur without patients noticing them but are detected in brain scans.

And, as the researchers discovered, they can have serious consequences. Compared with those who did not have a silent stroke, participants who had silent strokes had more than double the risk of experiencing delirium, a condition characterized by severe confusion, soon after surgery. They also had a twofold increase in probability of experiencing cognitive decline and a fourfold increase in probability of having an overt stroke (with recognizable symptoms) or ministroke (a temporary lack of blood flow to the brain) a year later.

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“What we demonstrated was consistent across all non-cardiac surgeries – so in all types of surgeries, we saw these strokes – and across all centres [involved in the study],” said co-principal investigator P.J. Devereaux, director of the division of perioperative care at McMaster University. “This establishes that it’s not infrequent.”

While family members sometimes notice cognitive or behavioural changes in loved ones after surgery, these changes tend to be dismissed as a consequence of the patients’ advanced age and exposure to anesthesia, and are expected to resolve over time, Dr. Devereaux said. What his study suggests, however, is in some patients, these changes may, in fact, be due to silent strokes, which do not improve on their own, but may lead to further problems.

The study was partly funded by the Canadian Institutes of Health Research and was led by researchers at the Population Health Research Institute of Hamilton Health Sciences and McMaster University. It followed 1,114 patients at 12 academic centres in nine countries, including Canada and the United States.

The researchers compared the results of patients’ cognitive assessments taken before surgery and a year after surgery. Patients also underwent magnetic resonance imaging (MRI) of their brains between two to nine days after surgery, using a technique that allowed researchers to determine whether the patients had experienced a recent silent stroke.

The research team did not include patients who had cardiac surgery in the study, since these procedures involve additional factors that can contribute to the risk of stroke, Dr. Devereaux said. It also focused on those who had elective surgeries, since acute conditions requiring emergency surgery would not have allowed researchers to take cognitive assessments. Nevertheless, Dr. Devereaux said, silent strokes are likely an issue for patients who undergo these other types of surgeries as well.

Dr. Devereaux said these findings pave the way for more research into how to tackle these strokes and prevent cognitive decline, such as potentially giving patients anti-coagulants.

“We certainly just want to make sure we avoid the scenario where someone’s loved one is different after surgery, and make sure we minimize any chance of that happening,” he said.

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Amy Yu, a stroke neurologist at Toronto’s Sunnybrook Health Sciences Centre who was not involved in the study, said the research sheds light on an issue that has received relatively little attention to date.

“Most research has focused on patients with overt strokes, and the study findings help draw attention to covert strokes,” she said in an e-mail. “The findings highlight the importance of more research into prevention and detection of covert strokes in the post-operative period.”

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