Anesthetics Analyzed - Sleep Week

ADDITIONAL CONTRIBUTORS Tanya Silverman

By Tanya Silverman

Photo by Martin von Haller Groenback.

It is not uncommon for a surgical doctor to inform a patient that they will be put “to sleep” for an operation. However, research developments indicate that this isn’t necessarily true.

“Anesthesia is not sleep,” says Dr. Emery Brown, an anesthesiologist based in Boston. “We put you in a state where you’re insensate, and very painful things don’t bother you. Which, by definition, is a coma.”

Brown works at Harvard as a professor of anesthesiology, at MIT as a professor of computational neuroscience, and at Massachusetts General Hospital as a practicing physician. He also serves as director of the Neuroscience Statistics Research Laboratory that aims to establish the neurophysiological definition of anesthesia.

The parallel between the suspended state of coma and anesthesia was a conclusion from Dr. Emery Brown’s 2010 study, “General Anesthesia, Sleep and Coma”, which was co-authored by Dr. Ralph Lydic, a Professor of Anesthesiology at University of Michigan, and Dr. Nicholas Schiff, a Medical Doctor at Weill Cornell Medical College.

Over the course of three years, these doctors compiled data to analyze the varying degrees of mental functions in patients that were anesthetized, asleep, or in a coma. A major component of their research involved the comparison of EEG readings (which are electrical readings in the brain activity represented by waveforms) of these three states of consciousness.

Through their research, Brown, Lydic, and Schiff observed the ways that EEG readings of patients under general anesthesia typically produce waveforms that progressively “increase in low-frequency, high-amplitude activity as the level of general anesthesia deepens.” By comparing the waveform reading to EEG measurements of those in comas or sleep states, the researchers determined that most of the brain activity readings of comatose patients “resemble the high-amplitude, low frequency activity seen in patients under general anesthesia” – rather than the waveforms of sleep.

The anesthetized state of being, Brown explains, can be considered a “reversible, drug-induced coma,” as doctors apply anesthetic drugs and hold the power to both actuate patients into this state and take them out of it.

Although using the term “coma” may sound startling to a person about to undergo surgery, Brown describes how he explains the anesthetic process to his patients:

“This is what I tell my patients: ‘I’m going to take care of your anesthesia for your surgery. While you’re having surgery, you’re going to be unconscious. You’re not going to be aware of anything that’s going on, you’re not going to feel any pain, you’re not going to remember anything that’s happening because you’ll be so unconscious, you won’t be able to make memories, and you won’t be moving around while the surgeons are operating.’”

During this explanation process, Brown makes a point to assure patients that he will be monitoring their heart rate, blood pressure, and breathing patterns.

“For patients, when you go into extra detail, they feel more comfortable,” he says.

While the aforementioned study that dissociates sleep from anesthesia is largely based on information collected from EEG readings, using EEG technology and considering brain activity is not currently a typical method that doctors employ to monitor and maintain a patient’s anesthetized state during surgery. The standard measurements that doctors monitor during anesthetized surgery include heart rate, blood pressure, breath, and temperature.

As of today, doctors excel in their understanding of these physical measurements, but Brown encourages them to also utilize EEG to monitor anesthetized patients. On an individual basis, the devices, which are very easy for doctors to apply, offer information on the patient’s brain state and response to drugs to further insure the patient’s confidence in the doctor’s awareness of their physiological state. On a broader basis, incorporating EEG into anesthesiology could supplement clinical and neurological studies.

“Every day, about 60,000 people go through a highly structured process of going in and coming out of general anesthesia and sedation,” says Brown. “Think of all those natural experiments that are occurring. If we start to pay far more attention to those patients, we’re going to learn a lot about the brain.”

One example that Brown points out is the deep state of alpha-coma, in which there are very specific EEG signatures. Certain states of anesthesia-induced unconscious produce very similar patterns.

Following the 2010 publishing of “General Anesthesia, Sleep and Coma,” Brown has worked on another study researching burst suppression, a phenomenon that involves sharp increases in normal, high brain activity which are interrupted by segments of sharply decreased activity. Brown found that the particular EEG pattern indicative of burst suppression can occur in several different planes of consciousness, such as in children with developmental disorders, in procedures involving induced hypothermia, in patients experiencing a coma, and in people who are administered general anesthesia.

By comparing all of the EEG information from these different situations, Brown and his co-authors determined that burst suppression is a similar “highly-structured, metabolic phenomenon” in all of these states that initially appeared very dissimilar from one another.

“Now that we know this, it gives us some insight into what state those patients’ brains are in when they’re in coma,” says Brown.

In addition to exploring coma, Dr. Emery Brown foresees many opportunities in the investigation of anesthetics to understand fields like pain, depression, locked-in syndrome, and brain disorders. Through this integrative approach, anesthesiology research can help contribute to all of these “clinical, neurophysiological phenomena,” which can, in turn, build on the understanding of anesthesia.

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