General anaesthesia may affect elderly minds

The reason cognitive function in the elderly may be affected after they receive anaesthesia has not been determined, but there seems to be a link between the type of surgery and the risk of injury.
The reason cognitive function in the elderly may be affected after they receive anaesthesia has not been determined, but there seems to be a link between the type of surgery and the risk of injury.PHOTO: ISTOCKPHOTO

For patients over 60, memory and ability to do complex mental tasks may be affected

It is not only the very young who are vulnerable to the long-term effects of general anaesthesia. The elderly are also at risk.

After a three-hour operation to remove her breast cancer four years ago, Madam Lee, a retiree who declined to give her full name, thought the worst was over.

The then 64-year-old continued with her treatment, which included chemotherapy and radiotherapy.

However, as the weeks went by, she felt different. First, she had some strange and vivid dreams. Then, she became more forgetful. Her short-term memory also suffered. "You could tell me to do something and, half an hour later, I would forget. I forgot a lot of appointments," she said.

Slowly - after a few months - her memory improved and her strange dreams stopped. She is largely back to her normal self now, except that her memory is deteriorating and she is becoming more forgetful again.

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Her symptoms paint a classic picture of post-operative cognitive dysfunction (POCD) - a condition in which memory and the ability to do complex mental tasks deteriorate after receiving anaesthesia.

However, she was never diagnosed. POCD is measured using special tests before and after surgery and anaesthesia, said Dr Shariq Ali Khan, a consultant at the Department of Anaesthesiology at Singapore General Hospital.

In routine care, where these tests are not done, POCD remains largely undiagnosed and unrecognised, unless it causes a significant impediment in the daily activities of life, said Dr Khan.

Why POCD occurs is an ongoing subject of research. Based on current evidence, certain factors, such as being older than 60 years and having pre-existing mild cognitive impairment, will increase one's risk of POCD.

It is likely that the brain of an elderly person is more susceptible to injury, said Dr Khan. This is because with age, there is a decline in the body's ability to bear physical stressors and repair itself.

However, the relationship between long-term POCD and general anaesthesia has yet to be proven.

In a study of 1,200 patients aged 60 and above, POCD occurred in 25 per cent of patients one week after surgery, and 10 per cent at the three-month mark.

Even two years after surgery, cognitive problems remained in 1 per cent of the study's subjects.

This suggested that patients with POCD can have different trajectories. Most recover completely while others display signs of dementia, said Dr Khan. Further research needs to be done to predict these trajectories with more certainty, he added.

There also seems to be a link between the type of surgery done and the risk of having POCD. For example, the incidence of POCD is higher after heart surgery, said Dr Khan.

One theory is that in heart surgery, there is excessive inflammation and micro-blood clot production, leading to brain cell injury and POCD. However, there is no conclusive evidence, he said.

Dr Khan tries to avoid exposing his elderly patients to general anaesthesia, whenever possible, by using alternatives such as regional anaesthesia or nerve blocks.

When his patients are under general anaesthesia, he uses monitors to avoid deep anaesthesia.

He also avoids using certain drugs, such as benzodiazepines, in vulnerable patients, as these drugs can increase the risk of post-surgery delirium.

Currently, local studies on POCD are virtually non-existent.

"In the near future, we hope to study the condition in our population in more detail," said Dr Khan.

A version of this article appeared in the print edition of The Straits Times on October 06, 2015, with the headline 'General anaesthesia may affect elderly minds'. Print Edition | Subscribe