There has been a long standing debate about whether undergoing anesthesia can trigger dementia (see article by Roni Jacobson in Scientific American, October, 2014). Despite large, well-publicized studies claiming there is no significant association between anesthesia and dementia, there are too many cases to dismiss the phenomenon as coincidence. The cases appear to be statistical outliers in that they are not the norm.
However, that does not make them any less real just infrequent.

What is widely accepted is that a portion of those who undergo general anesthesia experience what is called “postoperative cognitive decline.” This marked by lapses of memory and attention (mild to severe delirium) that lasts from a few hours to a few weeks before it clears. Most who experience anesthesia do not show these effects for more than a very brief time and do not go on to experience a progressive, irreversible dementia (disability and loss of independence).

The question is whether anesthesia causes or is the first link in those who experience progressive decline after anesthesia. One obstacle to answering this question is that we still do not understand how anesthesia really works. The effects are very diffuse and produced by the deactivation of proteins that modulate sleep, attention, memory, and learning. Anesthesia targets sleep and arousal by deactivating neural networks that allow various brain systems to communicate. Like any drug, anesthetics can trigger unforeseen adverse events or side effects that have nothing to do with anesthesia per se. Drugs are never as specific in action as many might think.

Animal studies have shown that anesthetics can increase the levels of toxic amyloid proteins in the brain. Furthermore, they can also inflame brain tissues. But it is a long way from animal models to human brain function. Epidemiological studies with humans so far have not clearly shown a link between anesthesia and triggering of dementia.

That being said, there are many complicating factors in pursuing answers to the question of casual links between anesthetics and dementia. There may be many individual differences in susceptibility to adverse effects of anesthesia. What are the factors that cause some of us to be more affected? Are there preexisting conditions that put some at risk for dementia? We know that postoperative decline is more likely with cardiac surgery. It is also more likely in the aged, the diabetic, and the hypertensive. Are there medical factors that predispose to dementia after anesthesia? How do we separate the effects of anesthesia from the general effects of the trauma of surgery?

We have few practical answers regarding the link between anesthesia and dementia so far. The best concrete advice given the risks and uncertainty is to avoid elective surgeries. Also, carefully consider the risks and benefits of any surgery.