Statistics and Neuroscience Can Improve Anesthesiology
Anesthesia is believed to act on the brain, but the standard protocol among anesthesiologists for monitoring and dosing patients during surgery is to rely on indirect signs of arousal, like movement and changes in heart rate and blood pressure. Research in brain science and statistical modeling has allowed Emery N. Brown, MD, PhD, an anesthetist at Massachusetts General Hospital in Boston, to safely give patients less anesthesia, which can be beneficial.
Dr. Brown has developed a theoretical (ie, neuroscientific) and analytical (ie, statistical) understanding of EEG brain wave measurements of patients under general anesthesia. Anesthesia’s effects in the brain produce specific patterns of brain waves, and monitoring them via EEG data can improve care.
“We should use neuroscience and neuroscience paradigms to try to understand what is happening in the brain under general anesthesia,” said Dr. Brown. “It is a neurophysiologic process that affects the brain and CNS, so how can it be that what is being developed in the neuroscience field is not being brought to bear on the question of the brain under anesthesia?”
In numerous papers over more than a decade, Dr. Brown has examined how various anesthesia drugs such as propofol, dexmedetomidine, and sevoflurane interact with various neuronal receptors, affecting circuits in different regions of the brain. Those neurophysiologic effects ultimately give rise to a state of unconsciousness—essentially a reversible coma—characterized by powerful, low-frequency brain waves that overwhelm the normal rhythms that synchronize brain functions such as sensory perception, higher cognition, or motor control.
Understanding anesthesia to this degree allows for practical insights. In a study published in October 2016 in Proceedings of the National Academy of Sciences, for example, Dr. Brown and colleagues showed how stimulating dopamine-producing neurons in the ventral tegmental area of the brain could wake mice up from general anesthesia. The study suggests a way that human patients could be awakened as well, which could lessen side effects, recover normal brain function more rapidly, and help patients move more quickly out of the operating room and into recovery.
In parallel with illuminating the neuroscience of general anesthesia, Dr. Brown has developed statistical methods to analyze EEG measurements in a way that anesthesiologists can apply to patients. Dr. Brown has shown that EEG readings of level of unconsciousness vary in characteristic ways based on the drug, its dose, and the patient’s age.
“The deciphering of how these drugs are acting in the brain turns out to be an important signal-processing question,” said Dr. Brown. “The drugs work by producing oscillations, these oscillations are readily visible in the EEG and change systematically with drug dose, class, and age.”
During every surgery, Dr. Brown uses real-time EEG readings to keep a patient adequately dosed without giving too much anesthetic. While treating an 81-year-old patient with cancer, Dr. Brown was able to administer about one-third of the dose considered necessary. This dose reduction can be especially important for older patients. “We already know you do not have to give older people as much, but it turns out it can be even less,” said Dr. Brown.
Older patients are especially susceptible to problematic side effects when they wake up, including delirium or postoperative cognitive dysfunction. Neuroscientifically informed ways to prevent giving too much anesthesia can help prevent such problems, said Dr. Brown.
As more anesthesiologists acquire knowledge and EEG equipment, the field can move to a model where doctors have a direct view of the patient’s brain when monitoring and maintaining their consciousness during surgery, said Dr. Brown.