Anaesthesia has been one of the greatest gifts of science and use of general anaesthesia is a routine part of surgical operations at hospitals and medical facilities around the world. However precise biological mechanisms of the drugs’ effects on the brain are only now being analyzed. In a review article published this week in the New England Journal of Medicine, scientists have tried to analyze a range of disciplines, including neuroscience and sleep medicine to understand how anaesthesia actually works.
Lead study author Dr. Emery Brown, an anaesthesiologist at Massachusetts General Hospital and professor at Massachusetts Institute of Technology said, “The biggest concern among patients is, “Am I going to wake up?” That happens extremely rarely but it’s a fear everyone has. I think the way to assuage the fear is to know what we are doing. But we can’t continue to comfort people if it’s a black box and I assure you it’s not going to go wrong.” Brown explained that general anaesthesia is reversible coma and not sleep adding, “From a laymen’s standpoint, you want to come in to surgery and basically know you are going to be well taken care of… We try to give patients the impression we understand what is going on, but we say you are going off to sleep when it turns out it’s not sleep, it’s more like a state of coma.”
Brown and his team comprising of Ralph Lydic, a sleep expert from the University of Michigan, and Dr. Nicholas Schiff, a coma expert from Weill Cornell Medical College in New York for the study compared the physical signs and electroencephalogram (EEG) patterns of general anaesthesia to those of sleep. They found significant differences between the states, with only the deepest stages of sleep being similar to the lightest phases of anaesthesia induced by some kinds of agents. While natural sleep normally cycles through a predictable series of phases, general anaesthesia involves the patient being taken to and maintained at the phase most appropriate for the procedure, and the phases of general anaesthesia at which surgery is performed are most similar to states of coma. Brow said, “People have hesitated to compare general anaesthesia to coma because the term sounds so harsh, but it really has to be that profound or how could you operate on someone? The key difference is this is a coma that is controlled by the anaesthesiologist and from which patients will quickly and safely recover.”
Brown went on to explain, “There are six areas of the brain where one drug is working.” It goes to the arousal centers in the brain stem, decreasing the levels of excitatory neurons; in the thalamus, the neural control center; in the cortex, the part of the brain that controls memory and consciousness; and then down the body to suppress action in the muscles and respiratory center. Only about 0.1 to 0.2 percent of all patients are aware of what is happening during the procedure, according to the Joint Commission, a regulatory committee that monitors safety at hospitals. Co-author Dr. Nicholas D. Schiff added, “Consciousness is a very dynamic process… And now we have a good way of studying it.”
This knowledge of the workings of anaesthesia may help in more ways than one. Brain disorders show similar neurological shutdowns on EEGs as those created by anaesthesia, suggesting this research may help discover new treatments. “If we can turn the brain on and off, maybe we can also turn off chronic pain syndrome,” Brown said.
The study was supported by National Institutes of Health grants as well as a National Institutes of Health Director’s Pioneer Award, and by grants from the James S. McDonnell Foundation.
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