Processed electroencephalogram and depth of anesthesia: window to nowhere or into the brain?

T RY to imagine this: a dozen operating rooms filled with patients having surgery while a lone anesthesiologist, gazing at live data and video feeds on a tablet computer or wall of computer monitors, manages their general anesthetic from a distant location. Far fetched? If you think so, consider that earlier this year an IBM computer dubbed “Watson” beat the best human contestants on the television game show Jeopardy, your iPhone can now talk back, and in some hospitals, the sickest patients are managed remotely by critical care physicians who may not be in the same time zone, let alone same building. Of course, there are many hurdles to clear (e.g., airway management and line placement) before this futuristic scenario could become reality for intraoperative anesthesia. Arguably one of the main ones is that only a trained observer using clinical judgment can determine the adequacy of unconsciousness and make appropriate adjustments in drug dosing to assure adequate surgical anesthesia. The article by Liu et al. in this issue of the Journal provocatively challenges that assumption and moves us a step closer to the future. Liu et al. tested the hypothesis that two machines—an infusion pump running software that calculates effect-site concentrations and a processed electroencephalographic device that analyzes a parameter called entropy—could outperform skilled manual control of drug titration by an experienced clinician during surgery using total intravenous anesthesia with propofol and remifentanil. In this context, entropy is essentially a measure of the disorder in the electroencephalogram signal; the electroencephalogram of an awake person will have high entropy, whereas an isoelectric electroencephalogram will have no entropy. What makes this randomized controlled trial interesting is that it took advantage of the fact that electroencephalogram entropy analysis generates measures of both hypnosis (i.e., state entropy [SE]) and analgesia (i.e., response entropy) and programmed the infusion controller to adjust the corresponding agent (propofol for hypnosis, remifentanil for analgesia) appropriately. Note that this was not a test of electroencephalogram-guided drug delivery per se; both the infusion controller and clinicians had access to the same electroencephalogram data. Rather it was about who or what did a better job using the information. And use the information they did. During the maintenance phase, the dual-loop controller made nearly triple the number of dosing modifications per hour than did the clinicians (21 vs. 8 for propofol and 28 vs. 10 for remifentanil). Performance was rated on how well the machines and skilled clinicians did at keeping patients within predetermined electroencephalogram parameters (e.g., SE 40–60, defined as adequate anesthesia; de-