What, Me Worry? I Can’t Remember What I Was Worried About!
For those of you looking for something else to worry about, here’s fodder for your next dose of Valium. For the past several years persistent rumors have been swirling about a possible connection between anesthesia and dementia. No, not demented anesthesiologists, although I could think of a few. There has been a recently flurry of activity in the caves in which neurobiologists roost, and the results are contradictory.
In June of last year the Mayo Clinic Proceedings published a study that found no association between anesthesia and dementia (http://www.mayoclinicproceedings.org/article/S0025-6196(13)00124-9/fulltext). Great! Then a study out of Taipei (http://bjp.rcpsych.org/content/204/3/188) published in July of last year suggests that having anesthesia for a procedure can double your risk of developing dementia within 3-7 years. Yipes! So who is right, and why such different results?
Let’s start with the study designs. Both used a case-control design, in which each identified “case” is paired with a person who did not develop the disease in question, matched by age and gender. In the Mayo Clinic study, the researchers started with identifying cases of dementia, then matched those with patients who didn’t get dementia, and looked for how much anesthesia each group had received. In the Taipei study the researchers started with identifying cases of anesthesia and then prospectively looking for dementia. Prospective means that you look for an outcome as it occurs, as opposed to looking at what has already occurred, as in a retrospective study. The Taipei study’s inclusion of a prospective component arguably strengthens it’s validity.
The main outcome measure in both studies is dementia, approached from different angles. Therefore, it would behoove both sets of researchers to have a darn good definition of dementia. I have no idea how the Chinese researchers defined dementia, since the British Journal of Psychiatry doesn’t let you look at the full article. The Mayo Clinic does:
“Information from the REP [Rochester Epidemiology Project, a large EMR database] was used to identify patients with primary dementia or AD [Alzheimer’s disease} in Olmsted County during the study period through the screening use of diagnostic codes followed by abstraction of relevant information from the medical record. Using this information, 1 of 3 behavioral neurologists who had wide experience in dementia and epidemiologic research reviewed the abstracted information to confirm the diagnosis of dementia, classify the type of dementia, and determine the year of onset. Diagnostic and Statistical Manual of Mental Disorders(Fourth Edition) (DSM-IV) criteria were used to define dementia. Each element of the DSM-IV criteria was documented separately, and a diagnosis of dementia was made only if all 3 criteria were present. Alzheimer disease was distinguished from other types of dementia based on available clinical and laboratory data using DSM-IV criteria (dementia with gradual onset and continuing decline and absence of any other conditions that could explain the deficits) and National Institute of Neurological and Communicative Disorders and Stroke and Alzheimer’s Disease and Related Disorders Association criteria.”
OK then. Pretty good definition I’d say. Here’s the problem: there are a million things that can cause dementia. The list is as long as your arm and includes (according to, guess who? the Mayo Clinic!):
vascular disease (problems with blood flow to the brain)
Huntington’s disease or Lewy Body Disease
heart and lung problems (a little broad there, but includes circulation and oxygenation issues)
infections, immune disorders, metabolic disorders, and endocrine problems
nutrition, medications, heavy meal poisoning
brain injury, hydrocephalus (water on the brain), or undiagnosed subdural hematoma (bleeding in the brain)
So now let’s look at our inclusion criteria for these studies again. Mayo Clinic: dementia, controls matched by age and gender. Taipei: anesthesia, controls matched by age and gender. Does age or gender appear anywhere in the above list of causes of dementia? They do not. Do any of the causes of dementia listed above show up in the control group criteria? They do not. We actually have no idea, based on these two studies, if the onset of dementia has anything at all to do with anesthesia. There are too many uncontrolled variables.
Why is this even a question? Why do we worry about anesthesia and dementia? Well, we have no idea how anesthesia drugs work so we have no idea what the long-term effects are, other than that we’ve been doing anesthesia for 150 years. So there’s that. But the real reason researchers have asked the question about a possible relationship between anesthetic agents and dementia is something that we’ve recognized for a long time but have recently invented a phrase for: post operative cognitive decline (POCD)
Post operative cognitive decline is a temporary decline in the ability to think and reason that is seen after major surgery, usually in the elderly. POCD is not, I repeat not, dementia. Dementia is a permanent and progressive condition. POCD, while it can last months and be debilitating, is not dementia. Again, there are a million reasons why patients might be cognitively impaired after major surgery, including all of the causes of dementia listed above. It is important for patients and families to be aware of the possibility of POCD, but please do not worry that the anesthesia for your loved-one’s heart surgery or femoral bypass is going to cause dementia. There is no evidence that it will.