Automatic control of anesthesia using two feedback variables.

A new controller of an ON/OFF type was implemented for halothane anesthesia. A proportional-plus-integral controller with time-delay compensation proved not to be robust enough for the known clinical situation, as shown both in computer simulations and in animal trials. The ON/OFF controller proved to be less sensitive to parameter mismatches, and repeated animal trials showed a short response time and acceptable steady-state tracking. A method for switching the controlled effect of the drug was also developed, since anesthetic agents have multiple effects. Mean arterial blood pressure and a measure of EEG frequency were chosen as controlled variables, both being depressed by halothane. A coordinator forces the system state as near the desired values of these variables as possible, given that only one drug is used.