Author: Meaghan Lee Callaghan
A brain under anesthesia might actually closely resemble a sleeping brain, according to a series of studies from a Finnish research group.
Study participants reported dreaming and recalled sounds played while they were under anesthesia, and EEG measurements recorded brain activity in reaction to stimuli. The researchers believe these findings could add to a growing body of research demonstrating that a brain under anesthesia is closely related to a bedtime brain.
“I think the main finding in our study is that the brains are working more than we had previously thought during anesthesia, and also maybe that this ‘anesthesia dream’ … resembles more normal sleep than we had previously thought,” said Harry Scheinin, MD, PhD, an anesthesiologist and adjunct professor of pharmacology at the University of Turku, a two-hour drive west of Helsinki.
The main experiment consisted of 47 male volunteers who were split into two groups: those who received dexmedetomidine (n=23) and those who received propofol (n=24). The researchers tested each participant for their level of responsiveness, and then used medication levels to a maximum of 1.5 times the original concentration to attain a state of presumed loss of consciousness. The participants were not under clinical anesthesia, noted Dr. Scheinin, and were not given any analgesics or muscle relaxants that would normally be used in a surgical setting.
While hooked up to an EEG machine, the volunteers were monitored and then exposed to stimuli including “emotional sounds,” described as unpleasant by the researchers, and Finnish sentences, both “congruent” and “incongruent”—for example, “the night sky was filled with shimmering tomatoes.” Immediately afterward, participants were awaken by voices and gentle shaking so that the researchers could question them immediately—all while still under the same drug concentration.
Overall, the EEG results showed that slow-wave power and frontal alpha activity increased as anesthesia deepened, although beta activity decreased. When roused, alpha and slow-wave activity reversed while beta activity remained the same.
After anesthesia, post-testing showed recognition of the emotional sounds that the volunteers had heard when they were under anesthesia—more often for those under dexmedetomidine (42%) than propofol (15%). With this, post-test results also found large amounts of brain activity regardless of whether the stimuli sentences were logical, which makes the researchers believe the brain is attempting to process the information even when under anesthesia. Also, nearly 90% of participants had “subjective experiences during unresponsiveness,” Dr. Scheinin said, which could possibly equate to dream states.
The researchers believe the findings, especially the high incidence of dreaming, are due to the study design. The quick rousing was key, said Dr. Scheinin, as was the maintained medication levels. “That enabled us to separate the effects of consciousness and the other effects of drugs, which could be specific or nonspecific. We had the same concentrations but different states of consciousness.”
Other researchers also credit the experiment’s unique findings to the study design. Kane O. Pryor, MD, the vice chair for academic affairs in the Department of Anesthesiology at NewYork-Presbyterian/Weill Cornell Medicine, in New York City, agreed that immediate rousing was crucial. “Normally it’s very difficult to assess this because you only ask people after they’ve woken up, and that relies on them having remembered,” said Dr. Pryor, who was not involved with the study.
Goal Is Consciousness Measurement System
Although Dr. Scheinin admitted that the thought of some semblance of consciousness while under anesthesia could be a scary thought, this work and that of others, he believes, could mean a safer experience when patients go under the knife. “Is it possible that all patients put to anesthesia are really conscious but they just don’t remember it afterwards?” he wondered. Studying levels of consciousness under anesthesia could one day lead to a measurement system, a “fingerprint,” Dr. Scheinin said, to recognize when someone is safely sedated and ready for surgery.
It’s a goal throughout the field, Dr. Pryor agreed. “This is part of a lot of interest in trying to have better methods to measure brain activity that might predict that somebody is having a conscious experience or that they may.”
Dr. Scheinin pointed out that, unlike in the studies, patients receive a mix of medications during surgery, which in rare instances can fail, such as when the amount of muscle relaxant successfully paralyzes a person but the anesthetic agent doesn’t lead to proper sedation.
“Awareness during anesthesia is still a problem. A minority of patients really are not sleeping, and they can recall what has happened—and that is really bad. So I think we need better ways to objectively measure the depth of anesthesia or the level of consciousness,” 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. 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.’”