Closed-Loop Control With Enflurane Under Generaland Regional Anesthesia: A Clinical Investiations

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 enflurane under general and regional anesthesia and compared with closed-loop performance was assessed with enflurane in the stability of hemodynamics and the vegetative nerve function, the quality of induction and emergence ,the quality of pastoperative analgesia , and the quantity of enflurane per hour.Methods: Fifty adult ASA I -II patients scheduled to undergo elective abdomen surgery were divided into two groups general anesthesia and general anesthesia combined with epidural anesthesia (n1=35,n2=15): closed-loop control general anesthesia combined with epidural anesthesia received combined inhale intravenous anesthesia after 4-5ml lidocaine was given through thoracic epidural cavity The process of maintenance was general anesthesia combined with epidural anesthesia controlled by the closed-loop target-controlled infusion system and at the same time4-5ml lidocaine was given through thoracic epidural cavity at the interval of 45min. an intra-operative target bispectral index of 55 in all cases;General anesthesia was induced using the low-flow fresh gas technique with enflurane under spontaneous respiration. Fentanyl 0.4 μ g · kg-1 and succinylcholine 100 mg were injected intravenously to facilitate endotracheal intubation after eyelid reflex disappeared. The both process of induction and maintenance was controlled by the closed-loop target-controlled infusion system, an intra-operative target bispectral index of 50 in all cases. Adequacy of anesthesia and change of hemodynamics, heart rate variability 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 wobble of the control variable.Results: The mean wobble (6.91%: 4.26%), the median performance error (-0.24%:2.01%) and the median absolute performance error (8.06%:5.48%) were not statistically difference, respectively. Although there was oscillation of the measured BIS around the set point, no patients reported awareness or recall of intraoperative events. During maintenance of anaesthesia, cardiovascular variables did not differ between two group. Cardiovascular parameters were stable in both groups. The duration of induction, emergence is different with Closed-loop control general anesthesia and general anesthesia combined with epidural anesthesia. The concentration of the end-tidal enflurane increases gradually with time tnen it was stable The curve of end-tidal enflurane concentration is not match with the predicted value by the model.Conclusions: Closed-loop control general anesthesia combined with epidural anesthesia was able to provide clinically adequate anesthesia with enflurane and kept the hemodynamics and vegetative nerve function stable. Closed-loop control generalanesthesia combined with epidural anesthesia show decreases in induction, and emergence time than closed-loop control general anesthesia. The used quantity of enflurane was decreased . Further studies are required to determine whether control performance can be improved by providing adequate vaporization of enflurane.