Brain Effects of General Anesthesia
New research is shedding light on the effects of general anesthesia on the brain and the body.
In the United States, nearly 60,000 patients receive general anesthesia for surgery every day. It causes specific patterns of activity in the brain, which can be viewed on an electroencephalogram (EEG). The most common pattern is a gradual rise in low-frequency, high-amplitude activity as the level of anesthesia deepens.
Emery Brown, MD, of Massachusetts General Hospital believes, “How anesthetic drugs induce and maintain the behavioral states of general anesthesia is an important question in medicine and neuroscience.”
His team investigated general anesthesia versus sleep and coma. They carried out a review of anesthesia studies from a range of areas, including neuroscience and sleep medicine.
“It may sound nitpicky, but we need to speak precisely about what this state is,” Brown says. “This paper is an attempt to start at square one and get clear definitions in place.”
He explained, “We started by stating the specific physiological states that comprise general anesthesia, specifically unconsciousness, amnesia, lack of pain perception and lack of movement, and then we looked at how they are comparable to and different from sleep and coma.”
The team compared the physical signs and EEG patterns of these states. They found significant differences, with only the deepest stages of sleep being similar to the lightest stages of anesthesia. General anesthesia essentially is a “reversible coma.”
“While natural sleep normally cycles through predictable phases, general anesthesia involves the patient being taken to and maintained at the phase most appropriate to the procedure,” they report in the New England Journal of Medicine.