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The risk of cognitive decline after surgery

New light has been shed on the post-operative cognitive decline common in older people.

Not so long ago, a 70-year-old was considered to be elderly and at high risk of experiencing complications following surgery, such as a heart attack, a stroke, a longer hospital stay or even death. Advances in anaesthetic and surgical techniques mean many older people are now safely having operations that were previously not possible.

A recent study in the British Journal of Surgery found that the number of people aged 75 and older having surgery doubled between 1999 and 2015, and US figures suggest that more than a third of all operations are now carried out on people aged 65 and older.

Common procedures include hip and knee replacements, back surgery and surgery for cancer, which is more likely to affect older people.

But, although surgery is safer for older people than it was a generation ago, it’s not completely without risks. “The older you are the riskier it gets,” says Auckland City Hospital specialist anaesthetist Dr Doug Campbell. “It’s an accelerating pattern as you go from 60 to 70 to 80. The risk doubles approximately every decade. There’s no fighting nature, despite the huge improvements in medical care.”

One common, but – until recently – mysterious complication of surgery in older people is cognitive decline afterwards. “People often say grandad was never the same after he had his surgery,” says Campbell. “Cognitive decline is a known complication following surgery in older patients, but the reason for it has been unclear.”

A new study of 1100 older patients from around the world – including 85 from New Zealand – has now found a possible explanation for this phenomenon. The NeuroVISION study, the results of which were published in the Lancet in August, found that one in 14 of the patients experienced what is called a covert or silent stroke following non-cardiac surgery. Unlike an overt stroke, which has obvious symptoms, a covert stroke can only be detected using a brain scan, such as an MRI.

All the patients in the study were given an MRI within nine days of their operation to look for evidence of covert stroke. A year later, they had cognitive tests, which showed that those who had had a covert stroke were twice as likely as those who didn’t to be experiencing cognitive decline.

Campbell, one of the lead researchers for the trial, says it’s hoped a second study will shed light on how to prevent these strokes following surgery. In the meantime, older patients need to know there is a 7% chance they may have a covert stroke after an operation, which increases their risk of cognitive decline.

“It is a relatively common complication and it has consequences that people need to be aware of.”

Age is not the only factor that increases the risks associated with surgery. Pre-existing health conditions such as high blood pressure, obesity or diabetes also raise the risk. A healthy 75-year-old is much less likely to have complications than an unhealthy one. Campbell recently developed a surgical-risk calculator to help patients and doctors weigh up the risks and benefits of surgery – particularly elective surgery such as joint replacement. NZRisk.com uses New Zealand data to provide information reflecting our unique ethnic mix.

Drs Tim Short, far left, and Doug Campbell. Photos/Supplied
One risk older people no longer have to worry about is dying as a result of being too deeply anaesthetised. Observational studies had suggested that using too much anaesthesia on older patients could slow recovery after surgery and cause heart attacks, strokes and death. However, using too little anaesthesia may mean patients are aware of what is happening during surgery.

A study funded by the New Zealand Health Research Council has now allayed concerns that deep anaesthesia is more risky for patients aged 60 and older. The study, led by Campbell’s colleague at Auckland City Hospital, Dr Tim Short, involved more than 6500 patients and ran over five years in 74 centres worldwide.

The results, which were published in the Lancet in October, showed that patients who had deep anaesthesia were no more likely to die in the year following surgery than those who had lighter anaesthesia.

“We were very reassured by the findings,” says Short. “It means you don’t run the risk of getting a lot of awareness in people if anaesthesia is too light, but it won’t kill you if it’s too deep.”

This article was first published in the January 25, 2020 issue of the New Zealand Listener.

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