December 29, 2010 — Despite what anesthesiologists may tell surgery patients, the brain under general anesthesia is not "asleep," it is placed in a reversible drug-induced coma, according to 3 neuroscientists who reviewed and synthesized the latest research in general anesthesia, sleep, and coma.
Their review, 3 years in the making, appears in the December 30 issue of The New England Journal of Medicine.
"Anesthesiologists use the term 'sleep' so as not to scare patients with the word 'coma,' " Emery N. Brown, MD, PhD, from the Department of Anesthesia, Critical Care, and Pain Medicine at Massachusetts General Hospital and Harvard Medical School, Boston, pointed out in correspondence with Medscape Medical News. In reality, however, general anesthesia is a type of coma.
Dr. Brown's coauthors on the review are Ralph Lydic, PhD, from the University of Michigan, Ann Arbor, whose expertise is sleep medicine, and Nicholas D. Schiff, MD, from Weill Cornell Medical College in New York City, who specializes in recovery from coma.
"This review was prompted by a recognition that common brain circuit mechanisms may underlie aspects of general anesthesia and recovery from coma and that thinking through the links across these phenomena and their distinction from the natural processes of sleep would reveal important insights," Dr. Schiff told Medscape Medical News.
The realization that general anesthesia and coma have more in common with each other than differences "is very exciting," Dr. Schiff said, "because it gives us new ways to understand each of these states.
"Measuring brain circuit mechanisms may lead to greater diagnostic accuracy and targeted therapeutic strategies for predicting and supporting the recovery process from coma after severe brain injuries," he added. Monitoring brain function under general anesthesia may also help in developing new sleep aids.
Nothing Mysterious About the Anesthetized Brain
The scientists note in their article that there is substantial overlap between the electroencephalograms of patients in coma and of patients during general anesthesia. "The [electroencephalogram] of the states of coma recovery can resemble those of the awake, general anesthesia, or sleep state, depending on how extensive the brain injury is and where the patient is in terms of recovery," Dr. Brown noted.
The team also notes that anesthetic drugs induce unconsciousness or alter arousal through actions at multiple sites in the cerebral cortex, brainstem, and thalamus.
Contrary to what is commonly stated, how these drugs create the state of general anesthesia "is not mysterious," Dr. Brown explained, and "there are multiple mechanisms even for a single drug."
General anesthesia, the scientists say, is functionally equivalent to brainstem death, and perhaps explains why some patients do not fully recover consciousness for several hours after general anesthesia, as well as why postoperative cognitive dysfunction could persist in elderly patients for several months afterward.
"One thing which is evident regarding recovery from general anesthesia is that it tracks the return of function in the brainstem from bottom (respiration) to top (eye-movements and arousal centers)," Dr. Brown noted.
Dr. Brown, Dr. Lydic, and Dr. Schiff hope their article will facilitate more informed discussions among anesthesiology, sleep, and coma researchers and lead to new approaches to creating the state of general anesthesia, sedation, and sleep, as well as new approaches to facilitating coma recovery.
They hope it will also lead to better education of the public about general anesthesia.
This research was supported by the National Institutes of Health, the James S. McDonnell Foundation, Massachusetts General Hospital Department of Anesthesia, Critical Care and Pain Medicine, and University of Michigan Department of Anesthesiology.
N Engl J Med. 2010;363:2638-2650.
