Associate Professor Mathew Summers
There is anecdotal evidence, and some research, suggesting that in older adults, exposure to a general anaesthetic may result in activation of cognitive decline and dementia, post-surgery. That’s become an increasing area of interest. The hypothesis is that something is happening during the general anaesthetic, either the chemical or the process of anaesthesia, that’s changing brain chemistry or function, and that’s triggering a development of a dementia, following the exposure to general anaesthetic.
At this stage, the recommendation to avoid general anaesthetic for risk of dementia is not founded. There’s not sufficient evidence to suggest that. There are large scale studies that have shown an increased risk of dementia following general anaesthetic. There’s an equivalent large scale study that found no increased risk of dementia following a general anaesthetic, and there’s a third large study that showed decreased risk of dementia following a general anaesthetic. So again, the research is all over the place. We don’t have very clear randomised control trial evidence in humans that general anaesthetic is negative. The research is based on retrospective correlational studies.
The way we can look at why anaesthesia is being linked as a concern for dementia, comes down to the notion of causality. The research that we have is retrospective, in that we look at people who have developed dementia and we see that there’s a higher rate of those people who have dementia who may have had general anaesthetic in the last five to ten years, than the same age that don’t have general anaesthetic. The difficulty with such retrospective correlational studies is they don’t demonstrate causation. They demonstrate coincidences, two things that happened at the same time. The way that we need to go forward is with much better research, to identify what the underlying mechanisms are. And there are a range of possible explanations. Even if we do find that general anaesthetic has a higher rate of dementia in older people, it still doesn’t mean that anaesthetic is the causal mechanism. The person needed surgery for a reason. They may have had another condition that increases their risk for dementia, independent of general anaesthetic. During the process of general anaesthetic there are changes in brain chemistry and brain function and brain activation. That may be the cause. There are secondary complications that happen because of the medical condition that they suffered from that may cause that. They may have already had dementia, and the reason that we notice when they’re in hospital that they have dementia, is because in the community, with early stage dementia, with all their routines and structures around them, no-one noticed. And it’s when we put that person in an unfamiliar environment such as a hospital, with lots of supervision and monitoring, that people are starting to notice that person’s cognitive functions aren’t quite as sharp as they should be. And medical practitioners start to take notice that their memory’s not working too well, and assessment happens and they’re discovered to have dementia. But that has nothing to do with a general anaesthetic. They always had those symptoms, they just weren’t noticed. So we just don’t know where in that puzzle the anaesthetic comes in.