Closed-loop control of propofol anaesthesia using bispectral index: performance assessment in patients receiving computer-controlled propofol and manually controlled remifentanil infusions for minor surgery

Background. In a previous study we used the bispectral index(BIS)^TM for automatic control of propofol anaesthesia, usinga proportional-integral-differential control algorithm. As controlwas less than optimal in some patients, we revised the constantsof the control algorithm. The aim of the current study was tomeasure the performance of the revised system in patients undergoingminor surgery under propofol and remifentanil anaesthesia. Methods. Twenty adult patients scheduled for body surface surgerywere enrolled. Anaesthesia was manually induced with target-controlledinfusions (TCI) of propofol and remifentanil. After the startof surgery, when anaesthesia was clinically adequate, automaticcontrol of the propofol TCI was commenced using the revisedclosed-loop system. For patients 11–20, effect-site steeringwas also incorporated into the closed-loop control algorithm.Adequacy of anaesthesia during closed-loop control was assessedclinically, and by calculating the median performance error(MDPE), the median absolute performance error (MDAPE) and themean offset of the control variable. Results. The system provided adequate operating conditions andstable cardiovascular values in all patients during closed-loopcontrol. The mean MDPE and MDAPE were –0.42% and 5.63%,respectively. Mean offset of the BIS^TM from setpoint was –0.2.No patients reported awareness or recall of intraoperative events. Conclusions. The system was able to provide clinically adequateanaesthesia in all patients, with better accuracy of controlthan in the previous study. There was a tendency for more accuratecontrol in those patients in whom the control algorithm incorporatedeffect-site steering. Br J Anaesth 2003; 90: 737–41