Under Anesthesia, Where Do Our Minds Go?

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To better understand our brains and design safer anesthesia, scientists are turning to EEG.

BY JACKIE ROCHELEAU

After experimenting on a hen, his dog, his goldfish, and himself, dentist William Morton was ready. On Oct. 16, 1846, he hurried to the Massachusetts General Hospital surgical theater for what would be the first successful public test of a general anesthetic.

His concoction of sulfuric ether and oil from an orange (just for the fragrance) knocked a young man unconscious while a surgeon cut a tumor from his neck. To the onlooking students and clinicians, it was like a miracle. Some alchemical reaction between the ether and the man’s brain allowed him to slip into a state akin to light sleep, to undergo what should have been a painful surgery with little discomfort, and then to return to himself with only a hazy memory of the experience.

Monitoring patients’ brains still isn’t something that medical boards require.

General anesthesia redefined surgery and medicine, but over a century later it still carries significant risks. Too much sedation can lead to neurocognitive disorders and may even shorten lifespan; too little can lead to traumatic and painful wakefulness during surgery. So far, scientists have learned that, generally speaking, anesthetic drugs render people unconscious by altering how parts of the brain communicate. But they still don’t fully understand why. Although anesthesia works primarily on the brain, anesthesiologists do not regularly monitor the brain when they put patients under. And it is only in the past decade that neuroscientists interested in altered states of consciousness have begun taking advantage of anesthesia as a research tool. “It’s the central irony,” of anesthesiology, says George Mashour, a University of Michigan neuroanesthesiologist, whose work entails keeping patients unconscious during neurosurgery and providing appropriate pain management.

Mashour is one of a small set of clinicians and scientists trying to change that. They are increasingly bringing the tools of neuroscience into the operating room to track the brain activity of patients, and testing out anesthesia on healthy study participants. These pioneers aim to learn how to more safely anesthetize their patients, tailoring the dose to individual patients and adjusting during surgery. They also want to better understand what governs the transitions between states of consciousness and even hope to crack the code of coma.

Your brain on anesthesia

Today’s anesthetic arsenal eschews Morton’s original formula for newer, safer drugs. These include ether-based inhalants such as sevoflurane and isoflurane, and the widely used, intravenous anesthetic propofol, all of which wear off faster than early ether-based anesthetics, enabling quicker recovery. (They are also less likely to cause fires and explosions in the operating room, a regular occurrence through the first half of the 20th century.) Despite these improvements, the risks associated with excessive sedation remain high. Depending on the complexity and length of surgery, between 17 and 43 percent of patients may have cognitive problems, typically in memory and executive functions.1 These typically last only one to two weeks after surgery, but few rigorous studies have examined changes in cognitive function in the general population beyond six months after surgery. For adults over 65, the most common surgical complication is post-operative delirium, which manifests as inattention and either disorganized thought or altered levels of consciousness. Delirium can last from a few hours to several months and may be an independent risk factor for longer-term cognitive decline.2  Delirium is also preventable in 4 out of 10 patients with pre-surgery cognitive evaluations and monitoring of blood biomarkers and EEG during surgical procedures, according to the American Society of Anesthesiologists’ Perioperative Brain Health Initiative, a national nonprofit that aims to promote brain health for older adults during and after surgery.

COUNT BACKWARD: General anesthesia redefined surgery and medicine, but over a century later it still carries risks, including the experience of “accidental awareness” on the operating table, reported by about 1 in 2 of 1,000 patients. Photo by Sergey Mironov / Shutterstock.

Some studies have shown that the risk of long-term cognitive damage and post-op delirium is highest for those who already have underlying cognitive vulnerabilities, such as Alzheimer’s or mild cognitive impairment, says Paul García, associate professor of anesthesiology at Columbia University, but so far there is no consensus. The risk factors remain unclear at least in part due to varying definitions of post-operative cognitive dysfunction used in studies.

A tiny subset of patients3 (about 1 or 2 in 1,000, although estimates vary) have reported “accidental awareness,” recalling some experience of their medical procedure during general anesthesia. For many patients, researchers point out, the experience is strange but inconsequential. However, about 50 percent of those patients have reported traumas that stick with them years later and have been shown to cause long-term psychological damage and even post-traumatic stress disorder…

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