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Uncovering the neurobiological basis of general anesthesia

The use of general anesthesia is a routine part of surgical operations at hospitals and medical facilities around the world, but the precise biological mechanisms that underlie anesthetic drugs' effects on the brain and the body are only beginning to be understood. A review article in the December 30 New England Journal of Medicine brings together for the first time information from a range of disciplines, including neuroscience and sleep medicine, to lay the groundwork for more comprehensive investigations of processes underlying general anesthesia

"A key point of this article is to lay out a conceptual framework for understanding general anesthesia by discussing its relation to sleep and coma, something that has not been done in this way before," says Emery Brown, MD, PhD, of the Massachusetts General Hospital (MGH) Department of Anesthesia, Critical Care and Pain Medicine, lead author of the NEJM paper. "We started by stating the specific physiological states that comprise general anesthesia – unconsciousness, amnesia, lack of pain perception and lack of movement while stable cardiovascular, respiratory and thermoregulatory systems are maintained – another thing that has never been agreed upon in the literature; and then we looked at how it is similar to and different from the states that are most similar – sleep and coma."

After laying out their definition, Brown and his co-authors – Ralph Lydic, PhD, a sleep expert from the University of Michigan, and Nicholas Schiff, MD, an expert in coma from Weill Cornell Medical College – compare the physical signs and electroencephalogram (EEG) patterns of general anesthesia to those of sleep. While it is common to describe general anesthesia as going to sleep, there actually are significant differences between the states, with only the deepest stages of sleep being similar to the lightest phases of anesthesia induced by some types of agents.

While natural sleep normally cycles through a predictable series of phases, general anesthesia involves the patient being taken to and maintained at the phase most appropriate for the procedure, and the phases of general anesthesia at which surgery is performed are most similar to states of coma. "People have hesitated to compare general anesthesia to coma because the term sounds so harsh, but it really has to be that profound or how could you operate on someone?" Brown explains. "The key difference is this is a coma that is controlled by the anesthesiologist and from which patients will quickly and safely recover."

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