“General anaesthesia is pharmacological coma, not sleep,” said Dr. Nicholas Schiff of Weill Cornell Medical College in New York, who worked on the study with Dr. Emery Brown of Massachusetts General Hospital and Dr. Ralph Lydic of the University of Michigan.
Their findings, published in the New England Journal of Medicine, represent a three-year exploration of the similarities and differences of sleep, anaesthesia and coma.
They said while doctors and patients commonly describe general anaesthesia as going to sleep, there are significant differences between the states, with only a bit of overlap between the deepest states of sleep and the very lightest phases of anaesthesia.
While sleeping usually involves moving through a series of phases, in general anaesthesia, patients are typically taken to a specific phase or state and kept there during the surgery. This phase most closely resembles a coma.
“The brain is becoming very, very quiet. The activity of the neurons is being dampened dramatically,” Schiff said in a telephone interview. “That is also true in coma.”
Schiff, an expert in coma recovery, said while no two brain injuries are alike, studying the way people come out of anaesthesia could be used as a model for predicting the stages of emerging from a coma.
“Although recovery from anaesthesia is much faster, there are hints that some of the circuit mechanisms have some overlap,” he said.
That could lead to monitoring tools and diagnostics to assess what stage of recovery a person with a coma is in, and it could be used to develop new strategies to help doctors bring patients back to consciousness.
Knowing more about the brain circuit mechanisms may also help researchers develop drugs to tweak specific brain circuits, Schiff said.
And the study should lend new insight into understanding general anesthesia, Brown, an expert in general anaesthesia, said in a statement.
“Anaesthesiologists know how to safely maintain their patients in the states of general anaesthesia, but most are not familiar with the neural circuit mechanisms that allow them to carry out their life-sustaining work,” he said.