In ambulatory surgery, anesthetic drugs must be administered at a suitable rate to prevent adverse reactions after discharge from the hospital. To realize more appropriate anesthesia, we have developed a hypnosis control system, which administers propofol as an anesthetic drug to regulate the bispectral index (BIS), an electroencephalography (EEG)-derived index reflecting the hypnosis of a patient. This system consists of three functions: 1) a feedback controller using a model-predictive control method, which can adequately accommodate the effects of time delays; 2) a parameter estimation function of individual differences; and 3) a risk control function for preventing undesirable states such as drug overinfusion or intraoperative arousal. With the approval of the ethics committee of our institute, 79 clinical trials took place since July 2002. The results show that our system can reduce the total amount of propofol infusion and maintain the BIS more accurately than anesthesiologist's manual adjustment.
For the purpose of maintaining hypnosis level of patients during general anesthesia appropriately, we have developed a hypnosis control system with a function of online identification of individual parameters. As the control strategy, model predictive control, which can take the dead time included in the bispectral index (BIS) response to propofol infusion into account rigorously, is used. The online identification function obtains pharmacodynamic parameters and the dead time for each individual patient from the BIS response for the first few minutes of anesthesia induction. With the approval by the Ethics Committee of Kyoto University Hospital, the system was applied clinically, and its effectiveness in maintaining hypnosis level accurately and reducing the amount of propofol infusion was confirmed.
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