Researchers at The Picower Institute for Learning and Memory at MIT and Massachusetts General Hospital are finding that combining brain monitoring equipment with drug-dosing algorithms could one day help anesthesiologists give patients just the right dose of anesthetic to stay sedated for the duration of medical procedures. This is called a closed-loop anesthesia delivery (CLAD) system.
Many patients’ biggest fear when undergoing surgery is waking up in the middle of it. Physicians and anesthesiologists do not want this either, as it often leads to more stress and complications in an otherwise easy procedure. Because of this, anesthesiologists will often give more anesthetic than necessary to keep patients sedated during medical procedures or when a patient is on lifesaving care.
While this is normally acceptable, sometimes anesthetics can be harmful to sensitive groups. “The common practice of using constant infusion rates can lead to overdosing,” the researchers wrote. “This observation is particularly relevant for elderly patients who at standard propofol infusion rates readily drift into burst suppression, a profound level of unconsciousness associated with postoperative cognitive disorders.” Studies also point to the idea that long periods of anesthesia in young children may cause behavioral problems.
A new, automated delivery system known as CLAD is being developed to help doctors administer the right dose of medication to each patient. CLAD technology looks at the data directly from the brain while the patient is unconscious, whereas anesthesiologists often rely on indirect markers such as heart rate or blood pressure to determine unconsciousness. The researchers collected these data-collecting brain markers by measuring changes in neural spiking activity while animal subjects were unconscious. They also looked at local field potentials (LFPs) which are large scale rhythms that the spiking produces.
The new device was tested initially by computer simulation to determine how the machinery would work under realistic conditions. After the first tests were run, the CLAD system was performed on rhesus monkeys. The monkeys were administered propofol, a common anesthetic. Over the experimental duration of 125 minutes, the CLAD system was independently allowed to take over for 30 minutes. The goal was to see if the brain monitoring device could bring the animals to a precise level of unconsciousness for 45 minutes, change them to a different level for another 40 minutes, and then bring them back to their original level for 40 more minutes. The doses were automatically adjusted every 20 seconds to ensure this happened. By changing the dosage so rapidly, researchers could ensure that the monkeys received just enough drug to stay sedated for 125 minutes. These findings were posted in PNAS Nexus in late October.
The Picower team acknowledged that there is more work to be done to make this type of anesthesia monitoring more suitable for human use. One of these steps is basing the current system off of an electroencephalogram (EEG), which can be measured from the scalp. The team could then determine markers for unconsciousness based on the data of human brain rhythms rather than monkey LFPs.
It is interesting to note that, while the current technology is trying to maintain unconsciousness, it can also help wake patients up.
