Researchers Develop More Accurate Brain Monitoring Method

It's been long known that anesthesia changes a patient's electroencephalogram readings, even if it has not been certain what the changes indicate. Now researchers at the Massachusetts General Hospital report that they've identified specific EEG patterns that indicate when patients leave and return to consciousness under propofol sedation.

The accuracy of this method, the details of which have been published online in the Proceedings of the National Academy of Sciences, could improve patient safety and anesthetic technique.

"The consequences of this could be huge, because it would mean we have found a brain state where we know patients will be unconscious and could monitor that brain state in the operating room using EEG," says lead author Patrick L. Purdon, PhD, a researcher in Mass General's department of anesthesia, critical care and pain medicine and an anesthesia instructor at Harvard Medical School.

Many of the presently available consciousness monitoring technologies simplify the EEG's complex patterns to deliver their readings, the authors note, which clinical studies say produces results that are about as accurate as monitoring drug concentrations in the blood and lungs - a standard operating procedure for anesthesia providers, along with watching vital signs.

To test out this newer reading - which builds on findings first reported last fall - the researchers closely observed the EEGs of 10 healthy volunteers undergoing propofol sedation. The dosage was slowly increased to a target level over the course of an hour, then slowly decreased. During the sedation, the patients were played a series of recorded words and clicks, which they were asked to identify by pressing buttons. When their responses stopped, the researchers correlated their unconsciousness to their specific EEG patterns.

David Bernard