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A Closer Look at Anesthesia and the Brain

Over 40 million people have surgery in the US each year so most people will have at least one general anesthetic during their lifetime, and many will have multiple anesthetics.

Patients have many different concerns about anesthesia, and hundreds of these questions have been published in the form of questions and answers on the NetWellness website. Common concerns include what I call the “big question” (“will I wake up after the surgery?”), and also its near-opposite (“will I wake up during the surgery!?”) It’s good to know that, while never risk-free, anesthesia has definitely become safer over the years. Although fatalities (about 1 in 20,000 to 1 in 200,000) or complications still occur as a direct result of anesthesia, anesthesiology has often been held as an example of an area of medical practice in which there has been a deliberate, and successful, attempt to improve safety.

Another concern, paraphrased and summarized, is this: “Doc, will I lose my mind?” With the administration of anesthesia being so common, the issue of whether there are persistent, long-term effects on the brain, deserves attention.

Revisiting the Effects of Anesthesia

Until recently, anesthetic gases were thought to produce no long term effects on the central nervous system. New studies have changed this view quite substantially. About a decade ago, we discovered that as many as 40% of elderly patients (over 65 – 70 years of age) experience a decline in mental function immediately after surgery. Most of these patients recover fully within 3 months but a small portion seems to have dysfunction that persists longer – for 6 months or more. Patients with problems that persist for longer than 6 months are even more likely to die before those who recover without brain dysfunction. This “syndrome” is now known as postoperative cognitive dysfunction (POCD) and is the subject of ongoing research in the lab, on experimental animals, and in people.

General anesthesia is not the same as ordinary sleep and is more like a kind of carefully controlled coma, with profound effects on the brain and other vital organs. The anesthetic drugs that cause this controlled coma are eliminated from the body over a period of hours to days. After general anesthesia, short-term (hours) impairment of cognitive (thinking) and psychomotor (movement associated with mental processes) performance is common and expected. However, until recently we have assumed that there are no long term effects on the brain after the disappearance of measurable amounts of the anesthetic drugs from the body. Instead, we have learned that anesthetics can have prolonged effects on brain function through alteration of receptors or of the expression of DNA (genes). There is even a phenomenon known as apoptosis or “programmed cell death”, which has been shown in animal experiments to occur after the administration of gas anesthetics during certain vulnerable periods of brain development.

Easy to See, Hard to Study

One of the main difficulties with POCD research is that patients who have general anesthesia are patients having surgery! Major surgery has major effects – on the cardiovascular system, and on the immune system, for example. The body is flooded with the chemical mediators of stress as it responds to the injury of surgery and mobilizes its resources for healing and recovery. Nobody is volunteering for surgery without anesthesia these days, so how can we possibly differentiate between the impact of surgery and the impact of anesthesia when we decide on the causes (and prevention) of the POCD syndrome?

Perhaps the most serious concern is that elderly patients with mild or undiagnosed dementia, a common disorder in our aging population, will somehow be “pushed over the edge” into full-blown dementia as a result of anesthesia and surgery. There are many anecdotal reports that suggest this is possible, but again we do not know whether anesthesia is the cause or whether it is simply an inevitable accompaniment of surgery.

One study that compared the incidence of POCD in patients who had regional anesthesia (i.e. nerve blocks and the like) versus those who had general anesthesia did not find a difference. This study makes it hard to believe that it is the anesthesia and not the surgery that is the culprit.

So far it has not been possible to determine whether there is a particular anesthetic drug that is worse (or better) in respect of POCD than others. This would allow us to modify the technique we use and limit any harmful effects. There is some evidence that the group of drugs called benzodiazepines – Valium and Versed are examples – are not a good choice in the elderly, however there are no clear best choices when it comes to drugs used for the induction and maintenance of anesthesia (a newer drug called dexmedetomidine is one possibility).

Finding the Cause of POCD

POCD is a problem with more questions than answers. The cause of POCD remains unresolved, but it is clearly an unfortunate and real outcome after surgery in a significant number of elderly patients. Fortunately, most people do recover. What is not clear is whether there is a connection between POCD and general anesthesia, how to predict those most at risk of a persistent decline in mental function (though age is clearly a factor in POCD, as is a previous stroke), and how to prevent it, other than by avoiding the surgical procedure altogether. Finally, in terms of POCD, there is currently no recognized limit to the number of properly conducted anesthetics that a healthy younger person may safely receive over a lifetime, or over any specified period of time. We simply do not know whether the same applies to mentally impaired elderly people.

Similar concerns have emerged with regard to the effects of anesthesia on the immature, developing brain (i.e. young children). Again, the evidence from clinical studies is hard to interpret and we await more answers from ongoing research. However this is a topic for another day.

Anesthesia arrived on the scene in 1846. Today we sometimes forget the enormous benefits and alleviation of suffering it provides, focusing only on possible harm. Anesthesia is a necessary accompaniment of surgery and the risks (and benefits) of anesthesia need to be considered every time a surgery, minor or major, is embarked upon. Patients should be sure to consult with their anesthesiologist and their surgeon prior to their operation and explain all of their concerns. The more information these doctors have about your medical history and about your concerns, the more likely your procedure will lead to successful short and long-term outcomes, and the more likely you are to awake and be fully returned to normal function.

For more information:

Go to the Anesthesia health topic.