Automated System Controls Medically Induced Coma

A new brain-machine interface (BMI) could automate the process of putting patients into a medically induced coma, opening the door to more advanced control of anesthesia.

Researchers at Massachusetts General Hospital (MGH; Boston, USA) and the Massachusetts Institute of Technology (MIT, Cambridge, USA) used software developed to analyze the activity of neurons to create algorithms to analyze electroencephalogram (EEG) patterns in real time and determine a target level of brain activity; for induced coma, that stage is burst suppression. Based on that target, they built an automated BMI that adjusts the flow of an anesthetic to achieve optimal feedback control, with real-time analysis of the continuous EEG readings fed back to the system to insure maintenance of the burst suppression target.

The burst suppression level is derived using burst suppression probability (BSP), an instantaneous probability measure of being in the suppressed state, representing the effect of the anesthetic propofol using a two-dimensional linear compartment model adjusted for experimentation. The researchers computed the BSP in real time from the EEG, segmented into a binary time-series by deriving a two-dimensional state-space algorithm. The resulting BMI device can promptly change the level of burst suppression without overshoot or undershoot, maintaining precise control of time-varying target levels of burst suppression.

Among the benefits of such a system would be the ability to maintain medical coma at a more precise, consistent level than can be done manually, as well as using lower doses of anesthetic drugs, a reduction possible with the computer-assisted technology. Additionally, by eliminating the need to devote one intensive care unit (ICU) nurse on each shift to the continuous monitoring of just one single patient, hospitals could significantly change staffing needs. The study describing the new system was published on October 1, 2013, in PLOS Computational Biology.

“To use an analogy that compares giving anesthesia to flying a plane, the way it's been done is like flying a direct course for hours or even days without using an autopilot,” said senior author Emery Brown, MD, PhD, of the MGH Department of Anesthesia, Critical Care and Pain Medicine. “Imagine that you’re going to fly for two days and I’m going to give you a very specific course to maintain over long periods of time, but I still want you to keep your hand on the stick to fly the plane. It just wouldn’t make sense.”

Burst suppression is an EEG marker of profound brain inactivation and unconsciousness consisting of bursts of electrical activity alternating with periods of isoelectricity (suppression). Burst suppression is targeted in medical coma to help recovery after brain injuries and to treat epilepsy refractory to conventional drug therapies. The induced coma often needs to be maintained for several hours or even days.

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Massachusetts General Hospital
Massachusetts Institute of Technology