science notes

Does Anesthesia Cause Dementia?

by T.J. Nelson

Does Anesthesia Cause Dementia?

W e all know that bacteria have become resistant to most of our life-saving antibiotics. The problem is so bad that we now do a risk/benefit analysis before going to a hospital. But there is another epidemic of iatrogenic (doctor-induced) disease that the medical profession is starting to lose sleep over: the growing realization that anesthesia and sedation cause dementia.

Let me start with an anecdote. I know a guy who ran a business doing minor repairs on scientific equipment—incubators, shakers, and so on. He was a lively fellow, an immigrant with many stories. One day we sent him an incubator. The repair took a long time, because unbeknownst to us he was scheduled for open heart surgery. When he finally brought it back he was happier than I'd ever seen him. He seemed deliriously happy to be alive. He showed us his scars and talked for an hour about his operation. One by one my colleagues remembered they had left an experiment running and excused themselves.

Then he brought in the incubator. The rotation was ridiculously slow. The thermometer was still broken. Instead of a shock absorber there was a piece of wood to prop open the door. He seemed proud of it, but it was clear he had had trouble fixing it. I can't say whether he eventually recovered or how long it took, but shortly thereafter he quietly retired.

Scientists call this postoperative cognitive dysfunction, called POCD for short. The literature says it is a common effect of general anesthesia. It lasts for a few weeks in some patients, and up to a year in others. In a few it is permanent. POCD is just as common under regional anesthesia and sedation as general anesthesia. Most practitioners call it a “rare adverse event.”

But is it? It's what the literature doesn't say that's frightening: this is exactly what we used to say about head injury. The problem is that there is no accurate way to measure cognitive function. Our best tool is Stanford-Binet, but patients certainly aren't going to sit down and take an IQ test, and it's not terribly accurate for individuals anyway. The tests we use to assess cognitive function in Alzheimer's patients—ADAS Cog, Mini-Mental, and so forth—are just crude approximations, and not useful in healthy people. So we don't have a reliable way of knowing how widespread the problem is.

Is there a way of avoiding anesthesia-induced dementia? This question will be hard to answer until we find a more accurate way of measuring cognitive function. What we do know is that POCD is not related to oxygenation level, so it cannot be blamed on anesthesiologists.

One question that naturally arises is whether POCD has any connection to Alzheimer's disease. The risk factors are similar: old age, lower education, cardiovascular disease, and comorbidity with other brain dysfunction such as stroke, Parkinson's, or vascular dementia.

Alzheimer's disease was first described in 1906, fifty years after anesthesia started to become widely used. It is tempting to speculate, but so far, there's no evidence of any connection. Finding one would be difficult, because it's tough to distinguish between different types of dementia. They may be confused with each other, or one may contribute to the other.

The current theory about POCD is that inflammation is the culprit. Inflammation, of course, is also present in Alzheimer's, but it could be simply an effect of brain injury, as toxins released from dying cells generate an inflammatory response. POCD also induces aberrations in beta-amyloid processing, but here again the significance is unclear: beta-amyloid in its so-called oligomeric form is toxic to the brain, but we have known for a long time that amyloid plaques are harmless, and we don't know whether amyloid is part of the pathophysiology or the body's way of attempting a repair.

I come in contact with lots of medical residents, and few care much about POCD. They're trained to ignore problems they don't know how to treat. That's understandable, because their time is valuable. The idea among practitioners is that undergoing a life-saving procedure is a good trade-off against a risk of cognitive dysfunction, or even Alzheimer's, later in life. But it's a factor that patients may need to consider, and they need to be informed of the potential risk.

This isn't a problem that only affects a small number of people. Almost everyone gets some form of anesthesia or sedation at some point in their lives. Many non-emergency diagnostic procedures require sedation. I shudder when I think about dentists giving general anesthesia to their patients and people undergoing elective surgery to improve their appearance.

Maybe the anxiety is overstated. But I still remember all the times Ronald Reagan had surgery, including after his attempted assassination, and I can't help wondering: could those procedures, intended to save his life, have actually accelerated his Alzheimer's?

nov 05 2014; updated nov 06 2014

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