Since the mid-1800s, doctors have used drugs to induce general anesthesia in patients undergoing surgery. Despite their widespread use, little is known about how these drugs create such a profound loss of consciousness.
In a new study that tracked brain activity in human volunteers over a two-hour period as they lost and regained consciousness, researchers from MIT and Massachusetts General Hospital (MGH) have identified distinctive brain patterns associated with different stages of general anesthesia. The findings shed light on how one commonly used anesthesia drug exerts its effects, and could help doctors better monitor patients during surgery and prevent rare cases of patients waking up during operations.
Anesthesiologists now rely on a monitoring system that takes electroencephalogram (EEG) information and combines it into a single number between zero and 100. However, that index actually obscures the information that would be most useful, according to the authors of the new study, which appears in the Proceedings of the National Academy of Sciences the week of March 4.
“When anesthesiologists are taking care of someone in the operating room, they can use the information in this article to make sure that someone is unconscious, and they can have a specific idea of when the person may be regaining consciousness,” says senior author Emery Brown, an MIT professor of brain and cognitive sciences and health sciences and technology and an anesthesiologist at MGH.
Lead author of the paper is Patrick Purdon, an instructor of anesthesia at MGH and Harvard Medical School.
Last fall, Purdon, Brown and colleagues published a study of brain activity in epileptic patients as they went under anesthesia. Using electrodes that had been implanted in the patients’ brains as part of their treatment for epilepsy, the researchers were able to identify a signature EEG pattern that emerged during anesthesia.In the new study, the researchers studied healthy volunteers, measuring their brain activity with an array of 64 electrodes attached to the scalp. Not only did they find patterns that appeared to correspond to what they saw in last year’s study, they were also able to discern much more detail, because they gave the dose of propofol over a longer period of time and followed subjects until they came out of anesthesia.
As the subjects became less responsive, distinct brain patterns appeared. Early on, when the subjects were just beginning to lose consciousness, the researchers detected an oscillation of brain activity in the low frequency (0.1 to 1 hertz) and alpha frequency (8 to 12 hertz) bands, in the frontal cortex. They also found a specific relationship between the oscillations in those two frequency bands: Alpha oscillations peaked as the low-frequency waves were at their lowest point.
When the brain reached a slightly deeper level of anesthesia, a marked transition occurred: The alpha oscillations flipped so their highest points occurred when the low frequency waves were also peaking.
The researchers believe that these alpha and low-frequency oscillations, which they also detected in last year’s study, produce unconsciousness by disrupting normal communication between different brain regions. The oscillations appear to constrain the amount of information that can pass between the frontal cortex and the thalamus, which normally communicate with each other across a very broad frequency band to relay sensory information and control attention.
The oscillations also prevent different parts of the cortex from coordinating with each other. In last year’s study, the researchers found that during anesthesia, neurons within small, localized brain regions are active for a few hundred milliseconds, then shut off again for a few hundred milliseconds. This flickering of activity, which creates the slow oscillation pattern, prevents brain regions from communicating normally.
Better anesthesia monitoring
When the researchers began to slowly decrease the dose of propofol, to bring the subjects out of anesthesia, they saw a reversal of the brain activity patterns that appeared when the subjects lost consciousness. A few minutes before regaining consciousness, the alpha oscillations flipped so that they were at their peak when the low-frequency waves were at their lowest point.
“That is the signature that would allow someone to determine if a patient is coming out of anesthesia too early, with this drug,” Purdon says.
Cases in which patients regain consciousness during surgery are alarming but very rare, with one or two occurrences in 10,000 operations, Brown says.
“It’s not something that we’re fighting with every day, but when it does happen, it creates this visceral fear, understandably, in the public. And anesthesiologists don’t have a way of responding because we really don’t know when you’re unconscious,” he says. “This is now a solved problem.”
Purdon and Brown are now starting a training program for anesthesiologists and residents at MGH to train them to interpret the information necessary to measure depth of anesthesia. That information is available through the EEG monitors that are now used during most operations, Purdon says. Because propofol is the most widely used anesthesia drug, the new findings should prove valuable for most operations.
In follow-up studies, the researchers are now studying the brain activity patterns produced by other anesthesia drugs.
The research was funded by the National Institutes of Health, including an NIH Director’s Pioneer Award, New Innovator Award and K-Award, and the Harvard Clinical and Translational Science Center.
Written by: Anne Trafton, MIT News Office
Sarah McDonnell | EurekAlert!
Staying in Shape
16.08.2018 | Max-Planck-Institut für molekulare Zellbiologie und Genetik
Chips, light and coding moves the front line in beating bacteria
16.08.2018 | Okinawa Institute of Science and Technology (OIST) Graduate University
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur
What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...
08.08.2018 | Event News
27.07.2018 | Event News
25.07.2018 | Event News
16.08.2018 | Life Sciences
16.08.2018 | Earth Sciences
16.08.2018 | Life Sciences