What happens in a brain under anesthesia? Researchers at the University of Turku, in Finland, are curious to find out, diving into brain waves and dreaming.
In a series of studies—the first batch of which was published in Anesthesiology and the British Journal of Anaesthesia in July—the researchers found interesting patterns of brain activity and responses to stimuli using electroencephalogram measurements in participants under different anesthetics.
In the studies, 47 male volunteers were divided into two groups, one receiving dexmedetomidine (n=23) and the other given propofol (n=24). The researchers tested each participants for his level of responsiveness at standard levels of anesthetic, and then the researchers increased anesthetic levels to 1.5 times that concentration, maintaining unresponsiveness to reach presumed loss of consciousness in the participants. The researchers monitored EEG readings throughout. When participants reached the presumed unconscious state, the team introduced stimuli, playing audio clips of Finnish sentences or “emotional sounds.”
In multiple analyses, the investigators found that whether or not the sentences were logical (e.g., “the night sky was filled with shimmering tomatoes”), the EEG showed responses that indicated the mind heard and processed the phrase in its muddled state (Br J Anaesth 2018;121:260-269). Regarding responsiveness to the “emotional sounds”—described by the university as unpleasant noises—participants under dexmedetomidine recognized the sounds nearly half the time (42%) in postanesthesia interviews, but more than the participants who received propofol (15%). Overwhelmingly in the postanesthesia interviews, participants reported dreaming while under anesthesia (86%) (Br J Anaesth 2018;121:270-280). The EEGs showed that slow-wave power and frontal alpha activity increased as anesthesia deepened, although beta activity decreased. When a stimulus was introduced, alpha and slow-wave activity reversed while beta activity remained the same (Anesthesiology 2018;129:22-36).
Although the research project is continuing and the authors acknowledge limitations, such as the instability of participants’ point of unresponsiveness, the team believes these findings may indicate that the brain maintains a level of consciousness when patients are under.
According to Harry Scheinin, MD, PhD, an anesthesiologist and an adjunct professor of pharmacology at the university, and one of the project leaders, anesthesia might not require full loss of consciousness and that it could resemble normal sleep more than previously thought. This could mean it is sufficient to simply disconnect the participants from the environment, he said.
“I don’t think it’s bad that brains are working more than we had previously thought and that anesthesia would resemble sleep more than we had previously thought,” Dr. Scheinin said in an interview with Anesthesiology News. “But there still is this problem of unintended awareness, so we need better ways to measure really objectively the level of sleep, especially when we are using these muscle relaxants because we are then putting the patients into a situation where they can’t show ‘hey, I’m awake.’”
—Meaghan Lee Callaghan