Emery Brown, MD, PhD

Emery Brown, MD, PhD, speaks at the annual Research Institute Symposium.

Emery Brown, MD, PhD, and a team of collaborating investigators from Massachusetts General Hospital are hoping to make a fundamental change in the way anesthesiologists think about the process of sedation—one that changes the focus from the body to the brain.

According to Dr. Brown, this shift in thinking is crucial when it comes to treating elderly patients (those over 60), who are statistically more likely to undergo medical procedures that require sedation, and more likely to suffer negative cognitive side effects as a result of being anesthetized.

Nearly 100,000 patients in the United States undergo anesthesia each day, and many of these patients are elderly. While under sedation, elderly patients run a higher risk of lapsing into a coma-like state called burst-suppression, which has been associated with poor cognitive outcomes after surgery. These post-operative disorders can persist for years, with devastating effects on patients and their families.

Brown and his team believe that many of these poor outcomes are due in part to elderly patients receiving more drugs than necessary to achieve and maintain sedation.

Speaking at the annual Mass General Research Institute Symposium last month, Brown said it has been a well-known fact for years that the elderly require smaller doses of anesthetic than average adult patients. Explanations for this difference have previously focused on age-related declines in cardiovascular, respiratory, liver and kidney function.

However, Brown and his colleagues believe the changes in neurobiology and neuroanatomy that occur during aging also play a key role in the processing of anesthetic drugs.

Brown explained that anesthetic drugs take control of the brain in a highly structured way by creating brain wave oscillations that interrupt normal communication between different parts of the brain.

In a normal brain state, there is free communication between neurons in the thalamus and the cortex, a connection that assists the brain in the processing of pain. When this communication is disrupted by the oscillations created by anesthetic drugs, the neurons cannot spike and therefore cannot transmit information back and forth.

Previous research conducted by Brown and Patrick Purdon, PhD, demonstrated that different classes of anesthetic drugs (such as propofol, ketamine and sevoflurane) produce different patterns of wave oscillations in the brain.

These brain wave patterns not only change based on the type of drug being used, but they also change in a significant way with age. “This is just the neurons getting older and not being driven by the drugs the same way,” Brown said.

By closely monitoring these brain waves over the course of a procedure, Brown has been able to limit the anesthetic dose that is needed to keep elderly patients under sedation.

In one case study involving an 81-year-old woman who underwent a six-hour procedure to have a large mass removed from her chest, Brown was able to maintain sedation with only 30 percent of the recommended dose for someone her age by monitoring her brain waves during the procedure.

In addition to their work with elderly patients, Brown and his colleagues have been monitoring the brain waves of pediatric patients, who also process anesthetic drugs differently than the average adult.

Patrick Purdon, PhD, in the laboratory

Patrick Purdon, PhD, and Emily Stephen, PhD, analyze brain activity during anesthesia-induced unconsciousness.

Brown is confident that the scientific evidence supports the use of brain waves as a key indicator of sedation, but he acknowledged there is plenty of work to be done to convince the medical community to adopt this method.

“I think the biggest block is a conceptual one,” he said, noting that anesthesiology has been traditionally viewed as a field of pharmacology. Anesthesiologists are trained to monitor the levels of sedatives in the blood and the lungs, he said, so it will require a large paradigm shift to get them thinking about anesthesia in terms of the brain.

Brown and his team are up to the challenge; however, and he believes they are starting to gain some traction. “We’re working specifically to set up guidelines for the elderly first. The need to take better care of the elderly right off the bat is compelling,” he said.

“We can change the way you manage the care of all these patients instantaneously if you adopt the ideas we’re talking about. Education is a key piece.”

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