UW study: Major surgery’s impact on brain is smaller than feared

UW study: Major surgery’s impact on brain is smaller than feared

Drape between patient and surgeons

A patient undergoes carpal tunnel surgery at UW Health. 




Despite fears surrounding major surgery and its potential impact on the brain, new research from UW-Madison shows that surgery is associated with only a minor decline in cognitive ability.

Robert Sanders, UW assistant professor of anesthesiology, said on average people’s cognition is “pretty much the same” after a major operation as compared to before, according to a study he authored that was recently published in the British Medical Journal.

“We should be relieved that the effect of major surgery is probably more subtle than we’ve been fearing,” Sanders said.

After analyzing records of more than 7,500 patients, Sanders and Bryan Krause, UW assistant scientist in anesthesiology, determined that having major surgery is associated with around a five-month decline in cognitive ability.

That five months of aging equates to someone scoring an average of a fifth of a point less on a cognitive test, Sanders said.

“For most people, if you think back cognitively to how you were performing five months ago, most of the time people won’t recognize a big shift in their cognition over that time period,” Sanders said.

The 7,532 patients that Sanders and Krause analyzed were recruited between 1985 and 1988 as part of a large study in the United Kingdom. In that study, participants between the ages of 45 and 69 were given a battery of cognitive tests, including word recall tests and mathematical reasoning tasks, every three to five years for 19 years.

Sanders and Krause linked this detailed cognitive performance data with the participants’ medical records to determine when the participants had major surgery and the impact that had on their test scores.

Robert Sanders


Many types of surgery were included, such as cardiac, thoracic, vascular, orthopedic, neurological, gynecological and general surgery. Major surgery was defined as a procedure that required at least a two-night hospital stay.

Over time, all of the patients’ scores decreased as they aged, but around the time that they had surgery, there was a slightly more dramatic decline, Sanders said. It is even possible that the five months of aging is an overestimate since medical and surgical technology has advanced since the 1980s and ‘90s.

But Sanders said it is impossible to disentangle what exactly caused the slight drop in cognitive performance. There are multiple factors in surgery that could drive changes in the brain, including anesthesia, the body’s reaction to the procedure and pain medications needed post-operation.

In addition, Sanders said needing surgery is associated with a change in health that could also be the cause.

“Since this is an observational study, we cannot identify surgery as the cause of the small change in cognition,” Sanders said.

Still, Sanders said he is confident that the small change researchers were able to uncover really does occur post-surgery, even if they can’t pinpoint the exact cause.

Sanders said because the study looked at a “very large number of subjects,” small changes, such as the fifth-of-a-point difference on cognitive tests, can still be detected. Sanders said other researchers may have overlooked their finding because they did not have a large enough sample size.

Bryan Krause


Another indicator that their finding is accurate is that Sanders and Krause found a large cognitive decline equivalent to 13 years of aging for patients who had a stroke. Sanders said this dramatic cognitive decline is expected for stroke patients, and the fact that their model found it means it’s working properly.

“The stroke is there to tell us, does our model work?” Sanders said. “That’s important because if we’re going to report a very small effect, we need to have confidence in our model that we can detect big changes and that we can detect small changes.”

There are some limitations to the study, Sanders said. The findings may not be applicable to people of color because non-whites were underrepresented in the study sample.

The study’s conclusions also might not apply to people over 70 because clinical diagnoses of cognitive decline, such as dementia, are more prevalent among older populations, Sanders said.

Overall, Sanders said patients should be comforted that undergoing major surgery poses only a “small risk” to the brain.

“We think it is reassuring,” he said.


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