Summary: A recent study published in JAMA shows that higher doses of general anesthesia are no more harmful to the brain than lower doses, providing reassurance for older adults undergoing surgery.

Key Takeaways:

  1. Recent findings from a multicenter clinical trial indicate that higher doses of general anesthesia are no more harmful to the brain than lower doses, challenging previous concerns about its adverse effects, especially in older adults.
  2. The study involving over 1,000 older patients found that the amount of anesthesia used did not impact the risk of postoperative delirium, suggesting that factors other than anesthesia, such as pain and inflammation, may contribute to this condition.
  3. The reassurance provided by these findings could help older adults make more informed decisions about undergoing anesthesia, promoting healthier and more confident choices.


General anesthesia allows millions of patients to undergo pain-free surgeries each year. Despite concerns about its potential adverse effects on the brain, especially at high doses, recent findings published in the Journal of the American Medical Association (JAMA) suggest that higher doses of anesthesia are no more hazardous to the brain than lower doses.

Debunking Anesthesia Cognitive Myths

The new study reports results of a multicenter clinical trial of more than 1,000 older patients who underwent surgery at four hospitals in Canada. Researchers at these hospitals, in partnership with colleagues at Washington University School of Medicine in St. Louis, found that the amount of anesthesia used during surgery did not affect the risk of postoperative delirium—a state that may contribute to long-term cognitive decline.

“Concern that general anesthesia harms the brain and causes both early and lasting postoperative cognitive disorders is a major reason that older adults avoid or delay life-enhancing procedures,” says Michael S. Avidan, MBBCh, the Dr. Seymour and Rose T. Brown Professor of Anesthesiology and head of the Department of Anesthesiology at Washington University.

“Our new study contributes to other compelling evidence that higher doses of general anesthesia are not toxic to the brain. 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 adds.

Ensuring Safe Anesthesia Levels

The dose of administered anesthesia historically has been a carefully calculated balance between too little and too much. Administering an inadequate amount puts patients at risk of experiencing intraoperative awareness. Despite advances in anesthesia care, about 1 in 1,000 people still experience unintended waking during surgery without being able to move or indicate their pain or distress. This can lead to suffering and lifelong emotional trauma.

“The good news is that the distressing complication of intraoperative awareness can be more reliably prevented,” says Avidan, the study’s senior author. “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 practice of general anesthesia should change based on mounting reassuring evidence.”

Other Factors Behind Postoperative Delirium

Previous smaller studies have suggested that too much anesthesia could be to blame for postoperative delirium, a neurological problem involving confusion, altered attention, paranoia, memory loss, hallucinations and delusions, among other symptoms. A common postoperative complication affecting about 25% of older patients after major surgeries, delirium can be distressing to patients and family members. It is typically temporary but has been linked to longer intensive care and hospital stays, other medical complications, persistent cognitive decline and higher risk of death.

To study the impact of minimizing anesthesia on postoperative delirium, Avidan and colleagues previously conducted a similar clinical study in more than 1,200 older surgical patients at Barnes-Jewish Hospital in St. Louis. The researchers used an electroencephalogram (EEG) to monitor electrical activity in the brains of patients during major surgery and adjusted anesthesia levels to prevent brain activity suppression, considered a sign of excessive anesthesia levels. They found that minimizing anesthesia administration did not prevent postoperative delirium.

“Delirium is likely to be caused by factors other than general anesthesia, such as the pain and inflammation associated with surgery. Future research should explore other avenues to prevent postoperative delirium. But 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 says.