Multivariable fuzzy control for the simultaneous administration of the anaesthetic and the analgesic drugs

A multivariable fuzzy controller developed for the simultaneous administration of the anaesthetic drug (propofol) and the analgesic drug (remifentanil), is presented. The controller was designed in order to achieve a steady state level of depth of anaesthesia (DOA) and to reduce the amount of drug infused. The multivariable fuzzy controller is based on linguistic rules that interact with three decision tables, one of which represents a fuzzy PI controller. Optimisation using genetic algorithms was used to determine the scaling factors of the fuzzy PI controller. According to the different possibilities for the DOA level and for the surgical stimuli, the multivariable controller defines the required change in the infusion rates of the two drugs. A patient model remifentanil was used to test the multivariable controller. The controller was able to adjust the remifentanil infusion rate according to the stimulus intensity, and takes advantage of the synergistic interaction to the change adequately the propofol infusion rate. The multivariable fuzzy controller was tested under different simulations, and responded efficiently to different induction profiles, set point changes and disturbances.