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The Body under General Anesthesia Tracks Closer to Coma Than Sleep

Studying brain waves and physiologic patterns in patients under general anesthesia might help researchers build new neurological models of disorders, such as comas and insomnia
under general anesthesia brain waves look like those of coma patient



ISTOCKPHOTO/SISTER SARAH

Patients undergoing significant operations, such as major cardiac or transplant surgery, typically require general anesthesia. But putting patients to "sleep" might not be the best way to describe the process, argued the authors of a new review paper, published in the December 30 issue of the New England Journal of Medicine.

What anesthesiologists are really doing is closer to putting patients—close to 60,000 each day in the U.S.—into a drug-induced coma. "It's a reversible coma, but it's nevertheless a coma," says Emery Brown, a professor of anesthesiology at Harvard Medical School and coauthor of the paper.

General anesthesia before major surgery dips brain activity (as measured by electroencephalogram, or EEG) down to levels akin to brain-stem death. For the most part, Brown has found that anesthesiologists talk about the process in colloquial terms, telling patients they will be "asleep," rather than "unconscious"—likely in an effort to not make a medical ordeal any scarier than it already needs to be.

That approach is doing both patients and scientists a disservice, he argues.

"It would be nice if your anesthesiologist could explain where drugs are going to be working," Brown says. Many clinicians, however, might be hard pressed to offer detailed neurological explanations for how each compound they administer is working on the nervous system. They are more likely to think of it in terms of "we turn the knob and they go to sleep," says Michael Alkire, an associate professor of anesthesiology at the University of California, Irvine, who was not involved in the new paper.

Inducing a coma-like state does require careful monitoring, breathing and temperature support as well as a delicate balance of "hypnotic agents, inhalational agents, opioids, muscle relaxants, sedatives and cardiovascular drugs," Brown and his colleagues noted in their paper.

The mechanisms behind this concoction, carefully devised though it might be, are not always well comprehended. Long thought of as a "black box," anesthesia now "can be explained and understood—it's not a mystery," Brown says. And researchers can further help to clear the field's fog by expanding the field of anesthesiology to collaborations with experts in other fields, such as sleep and coma research.

Although anesthesiology and research on sleep and coma generally carry on independently of one another, "there's a way to think about them all in the same framework," Brown explains. And that common frame should be neuroscience, he says.

Alkire agrees that the coma model "is more appropriate," and that "shifting toward that view is going to be helpful" in moving the field forward. And bringing the disparate fields, including researchers from sleep and coma work, together makes sense because "it's all the same fundamental neuroanatomy."

A push for more detailed neuroscience in the field might also help drive research toward new, more effective methods. Diethyl ether was a revolutionary tool in the 19th century that could knock people out before surgery, but it had some unpleasant side effects. "Now we need nuance" and more targeted tools like those cropping up in other areas of medicine, such as cancer treatment and screening, Brown notes.

Anesthesia, Alkire says, "is still kind of on the level of 'we have a big hammer, and we hit you on the head, and you get knocked out.'" He and his colleagues have been working to find more "regional brain anesthesia that would change the state of consciousness," he explains. "I think we have a ways to go" he says but notes that they have had some promising leads by zeroing in on the thalamus in animal studies. But even if clinicians might not yet have more delicate tools to dip patients into surgery-ready unconsciousness, Alkire notes, "understanding how it works puts you in a position to do better anesthetics eventually—if not with the agents you have right now."

And taking a deeper look at how drugs are working during anesthesia might also yield helpful models for different neurological disorders, Brown says, noting the similarities between EEGs in patients under general anesthesia and those in comas.

On the more mundane front, advances in anesthesiology might also help with treatments for insomnia—but not in the ways one might think.

Traditional treatments often work on the same mechanisms as the drugs given to anesthetize patients before surgery, thus helping people conk out, but not necessarily replicating normal sleep patterns. By taking a closer look at the mechanisms at work during general anesthesia—and how some of the more widely prescribed sleeping meds behave in the brain—"we can ask 'is that the way we want to [treat insomnia]?'" Brown explains.

And those advances in turn could feed back into the field of anesthesiology, helping to reduce side effects of general anesthesia, such as postoperative cognitive decline. Better understanding of the coma-like state of general anesthesia could also shed light on patients who are in a more permanent vegetative state, who upon waking go through very similar stages as those coming up from general anesthesia—albeit much more slowly. The key, says Brown, is "taking time to understand these mechanisms" and applying them to fine tune the proverbial hammer—a challenge that he and his colleagues hope to announce progress on in the coming months.

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