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Mental Deficits After Surgery

Posted by medconsumers on April 1, 2002

Mental Defecits After Major Surgery: The Search For Explanations
by Maryann Napoli

It took about ten years for the rumors to surface after coronary-artery bypass surgery was first introduced in the late 1960s. Some people had mental deficits that persisted long after they had been discharged from the hospital. The initial recipients of bypass surgery were primarily men in early middle age, so it should have been difficult for surgeons to dismiss the reports as unrelated to the operation. But dismiss they did, and the researchers would not take on the subject for another 10 years. Now there is mounting evidence that cognitive decline can occur at any age, not only as a result of coronary-artery bypass surgery but other major operations as well. Those most likely to be afflicted, however, seem to be elderly people who undergo an operation of long duration.

Had coronary-artery bypass surgery not rapidly become one of the most common major operations in the U.S., we might never have learned about its adverse cognitive effects that include memory problems and difficulties processing information. But, in time, the research could not be ignored. By the 1990s, several studies with long-term follow-ups found the incidence of cognitive decline to be highest right after the operation, but decreasing over time. At discharge, 50-80% of the people showed cognitive dysfunction, 20-50% at six weeks, and 10-30% at six months. These studies were conducted at a time when the age of a person undergoing coronary-artery bypass surgery had been slowly rising to the current average of 66 years.

Last year, a study conducted at Duke University Medical Center provided even longer follow-up information on 172 people (mostly male with an average age of 61 years) with much more sobering results. Five years after surgery, 42% still showed cognitive dysfunction (New England Journal of Medicine, 2/8/01).

These adverse effects had long been attributed to the use of the machine that takes over the function of the heart during all major chest operations. The heart-lung machine not only cools the heart, but also temporarily paralyzes it so that the surgeons can operate. The patient’s blood is diverted to the heart-lung machine, where oxygen is introduced and carbon dioxide removed, before the blood is returned to the body. Tiny air bubbles obstructing the blood flow to the brain were identified as a suspected main cause of cognitive deficits. Consequently, some surgeons have been experimenting with what they call the off-pump version of coronary-artery bypass surgery, now used in 20% of all such operations performed in the U.S.

Last month, the largest randomized clinical trial to compare both techniques published discouraging results in the Journal of the American Medical Association. The 420 participants (mean age 61 years) were facing their first coronary-artery bypass surgery. All had been randomly assigned to either on-pump (the standard procedure) or off-pump surgery. Psychologists had tested the participants before and after the operation.

The off-pump group did better at three months, but by one year after surgery, the rate of cognitive dysfunction was about the same for both groups (32%). The trial’s authors speculate that the off-pump technique itself might be just another source of cognitive deficits. Or, factors other than the heart-lung machine could be the cause of cognitive decline. And general anesthesia had already been identified as a possible explanation for the delirium, confusion, and cognitive dysfunction commonly observed in elderly people immediately after undergoing any form of major surgery. Research dating back to the 1950s showed that these symptoms may persist in some elderly people for months and even years after major surgery.

To fill a large information gap about cognitive decline in the elderly after non-cardiac major surgery, an international team of researchers looked at a range of possible causes-not just general anesthesia. Among them were low blood pressure and postoperative infection. The 1,218 study participants, aged 60 years and older, were given neuropsychological tests pre- and postoperatively.

“We confirmed unequivocally that anesthesia and surgery cause long-term postoperative cognitive decline in the elderly and that the risk increases with age,” concluded the authors of this study that was published in the Lancet (3/21/98). Of the 10% whose cognitive dysfunction continued three-months after surgery, advanced age was the only relevant factor. The authors noted that their findings could actually understate the problem because the participants were not especially ill, physically or mentally, before surgery. They also believe that more research must be conducted to determine whether postoperative cognitive dysfunction is a permanent disorder.

What you can do

-Make sure the operation is necessary by getting a second opinion. Coronary-artery bypass surgery, for example, is notoriously overdone. No major operation has been subjected to so many large-scale clinical trials, often comparing it to drug therapy. Results consistently show that a huge percentage of people who undergo this operation can be just as effectively—and more safely—treated with drug therapy. For a second opinion consultation, consider a trip to the Lown Cardiovascular Center in Brookline, Massachusetts (617/ 732-1318).

-It is not known how many people are informed that mental deficits are a possible risk of major surgery, or how many people are given an option of other forms of anesthesia when possible. The subject is worth a pre-surgical conversation with the surgeon and the anesthesiologist.

(April 2002)

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