| Objective: The Bispectral Index (BIS) is an electroencephalogram-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 isoflurane and compared with the traditional manual control inhalation anesthetic technique in the stability of hemodynamics, the quality of induction and emergence, and the quantity of isoflurane per hour.Methods: Thirty adult patients scheduled to undergo elective abdomen surgery were enrolled. All the patients were injected propofol (1.5-2mg ? kg-1 ) intravenously till the eyelid reflex was disappeared ,then Fentanyl(0.4μ g ? kg-1) and pipecuronium(0.08-0.1 mg ? kg-1 ) were injected intravenously to facilitate endotracheal intubation.. The process of maintenance was controlled by the closed-loop target-controlled infusion system. Meanwhile, in the manual control group, anesthesia processes were controlled with isoflurane vaporizer with an intra-operative target bispectral index of 50 in all cases. Adequacy of anesthesia and change of hemodynamics and the concentration of isoflurane 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.
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