MONDAY, June 10, 2024 (HealthDay News) -- Older adults who avoid surgery because they fear general anesthesia will cause thinking declines need not worry, researchers report.

A study of more than 1,000 patients who had heart surgery at four hospitals in Canada found that the amount of anesthesia used did not affect the risk of delirium after surgery. Post-surgery delirium may contribute to cognitive decline.

How much anesthesia to give requires striking a delicate balance between too much and little. About 1 in 1,000 people wake up during their surgery, unable to move or signal their pain or distress. This can cause lifelong emotional trauma.

"The good news is that the distressing complication of intraoperative awareness can be more reliably prevented," said senior study author Michael Avidan, head of anesthesiology at Washington University School of Medicine. "Anesthesia clinicians can now confidently administer a sufficient dose of general anesthesia, providing a margin of safety for unconsciousness, without being concerned that this will put their patients' brains at risk."

The new study adds to other "compelling" evidence that higher doses are not toxic to the brain, he added in a university news release.

Previous smaller studies have suggested that too much anesthesia could cause postoperative delirium, which affects about 25% of older patients after major surgery. Its hallmarks include confusion, altered attention, paranoia, memory loss, hallucinations and delusions. 

Though it is usually short-lived, this delirium has been linked to longer stays in intensive care, persistent thinking declines and a higher risk of premature death.

"Dispelling the misleading and pervasive message that general anesthesia causes cognitive disorders will have major public health implications by helping older adults make wise choices regarding essential surgeries, which will promote and sustain healthier lives," Avidan said.

The new study included 1,140 patients who had heart procedures with a high rate of complications after surgery. 

Roughly half had anesthesia adjusted based on electroencephalograms (EEG) that monitored electrical activity in their brains. Others, in a control group, received usual care without EEG monitoring.

The monitored patients received almost 20% less anesthesia and had 66% less time with suppressed electrical brain activity than the control group. 

Both had similar rates of delirium -- about 18% -- in the first five days after surgery. They had similar complication rates, length of hospital stays and risk of premature death for a year after surgery. 

Significantly, almost 60% more patients in the lower-dose anesthesia group had undesirable movements during surgery. These could have negatively affected the procedure.

The findings were published June 10 in the Journal of the American Medical Association.

"We can now confidently reassure our patients that they can request and expect to be oblivious, immobile and pain-free during surgical procedures, without worrying about general anesthesia damaging their brains," Avidan said.

More information

There's more about types of anesthesia and their side effects at the Cleveland Clinic.

SOURCE: Washington University School of Medicine, news release, June 10, 2024