Cognitive Changes After Anesthesia

“Everything seemed normal until after the operation.”

I can’t tell you how often I’ve heard some variation on those words. My medical specialty is cognitive and behavioral neurology, which translates into seeing a lot of patients with cognitive impairment. When I’m trying to figure out the cause of a cognitive change, it’s helpful to figure out when the first changes were noticed.

About 14 percent of the United States population is over the age of 65.

At least half of those over the age of 65 will have at least one surgery. That’s not a small number.  

It’s been estimated that about 7 to 15 percent of the elderly who undergo an operation will have some form of neurological adverse outcome. That percentage doesn’t even include cognitive changes such as post-operative delirium, a state of confusion which has been tied to all kinds of health concerns, such as longer hospital stay and functional decline after discharge from the hospital. Estimates of post-operative delirium range from 10 to 50 percent, though the risk varies depending on the type of surgery, age and other medical problems. The statistics above also don’t necessarily include other, more subtle cognitive changes.  

Traditionally, surgeons have concerned themselves with mortality, or the quantity of life, as a primary marker of surgical success. If the patient had a higher risk of dying after the surgery, things had to change.

  But what about the quality of life?  What if patients live for a long time, but lose their mind in the process?

The last several years have seen increased attention spent on cognitive outcomes after surgeries.  There’s been a lot of debate. For one thing, often cognitive functioning has not been well assessed prior to the surgery.

I’ve often found that when pressed, families can describe subtle cognitive changes that predate any operation, which became more obvious after surgery. In that case, surgery isn’t causing cognitive decline, but exacerbating it.

Another argument is what it is about a surgery that increases risk. Certainly some surgeries, such some of those performed on the heart, can increase the risk of strokes which could alter independent functioning after leaving the hospital. Those risks must be weighed against the risks of not having a surgery, which in some cases could mean probable death in a short period of time.

Or maybe it’s not actually the surgery, but the anesthesia given. Certainly there are many surgeries that shouldn’t be done without sufficient anesthesia, but does the amount of drug impact cognitive outcome? 

Anesthesiologists can vary the amount of drug they give. Some patients prefer to be almost awake during surgeries, whereas for others that would be a horror. Even if higher doses of anesthesia does worsen cognitive outcomes afterwards, there are dangers to lighter doses.

The patient may move while under the scalpel. They could have a strong autonomic reaction, with dangerously high blood pressures or heart rates. Or they may suffer psychologically from the memory of being awake during significant surgery.

Anesthesia Dose and Cognitive Outcomes

Doctors have tried to answer the question of how anesthesia dose impacts cognitive outcomes in a variety of different ways.

One technique uses something called bispectral electrocorticography (BIS). This gives a superficial view of brain activity while the patient is in the operating room.  Early studies suggested that a low BIS value was associated with mortality, but other studies have found no such association. 

Rather than looking at mortality, other studies simply study the incidence of post-operative delirium, recognizing that post-operative delirium is also connected with bad outcomes. When looking at post-operative delirium, studies suggest that higher sedation does seem to increase the risk—one study done at the Mayo Clinic found that the post-operative risk of delirium of those in deep sedation was almost twice that of those who underwent lighter sedation. 

Despite the association between delirium and dementia, however, Dijkstra and colleagues found no  relationship between exposure to anesthesia and long term cognitive decline in a 1998 study. Other health complaints were the more important predictor.

What does all this mean? It means there are a lot of unanswered questions. While deeper anesthesia may lead to more post-operative delirium, the consequences of that delirium regarding long-term cognitive outcomes are unclear. This is especially true when one considers that many who have poor outcomes may have already been in the early stages of cognitive decline before surgery ever began.

So what are some practical things for an older person to consider before undergoing anesthesia for surgery? It may be best just to recognize that there is a higher risk of transient confusion afterwards. While this almost always improves, in some people they may not get back to where they were cognitively before the surgery. That may be especially true if there were already some signs of memory problems.  That said, there are some real benefits to anesthesia and these surgeries as well, which will need to be weighed against these potential risks. 


Jacqueline Leung, Anesthetic Depth and Postoperative Cognitive Outcomes, UCSF Memory and Aging Center Grand Rounds, June 26, 2015. 

Jeanette B. Dijkstra PhD, Martin P.J. Van Boxtel MD, PhD, Peter J. Houx PhD and Jellemer Jolles PhD.  An Operation Under General Anesthesia as a Risk Factor for Age-Related Cognitive Decline: Results from a Large Cross-Sectional Population Study. Journal of the American Geriatrics Society, Volume 46, Issue 10, pages 1258-1265, October 1998. 

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