Closed-Loop Control Of Anesthesia With Enflurane: A Clinical Investiations

Object: The Bispectral Index (BIS) is an electroencephalogran-derived measure of anesthetic depth. A closed-loop anesthesia system was built using BIS as the control variable, a proportional-integral-differential incorporated with adaptive control algorithm, and a target-controlled infusion system as the control actuator. Closed-loop performance was assessed with enflurane and compare with the traditional manual control inhalation anesthetic technique in the stability of hemodynamics, the quality of induction and emergence, and the quantity of enflurane per hour.Methods: Thirty adult patients, scheduled for the selective abdomen operation, were randomly divided into 2 groups(n=16, 14). General anesthesia was induced using the low-flow fresh gas technique with enflurane under spontaneous respiration. Fentanyl 4 ug/kg and succinylecholine 100mg were injected intravenously to facilitate endotracheal intubation after eyelid reflex disappeared. The control group, the all process of induction and maintenance was controlled by the closed-loop target-controlled infusion system. Meanwile, in the manual controll group, anesthesia processes were controlled with enflurane vaporizer with an intra-operative target, bispectral index of 50 in all cases. Adequacy of anesthesia and change of hemodynamics and the concentration of enflurane during closed-loop control were assessed clinically and by calculating the median performance error, the median absolute performance error, and the mean offset of the control variable.Results:The median performance error(1.6%; 3.97% ), the median absolute performance error(5.90%: 8.48%), were not statistically difference, respectively. The mean wobble(5.91%; 9.74%) and the mean offset of the BIS from the set point(0.91%; 2.15% ) were lower than manual group(P=0.01). Although there was oscillation of the measured BIS around the set point, no patients reported awareness or recall of intraperative events. Cardiovascular parameters were stable in both groups during maintenance of anesthesia. The duration of induction, emergence and responses is not different with manual group. The concentration of enflurane increases gradually with time and the curve of end-tidal enflurane concentration is not match with the predicted value by the model.Conclusions: The system was able to provide clinically adequate anesthesia with enflurane and kept the hemodynamics stable. But closed-loop control did not show any decreases in induction, emergence and respond time than the manual group. The used quantity of enflurane was not decreased either. Further studies are required to determine whether control performance can be improved by providing adequate vaporization of enflurane or advancing the method.