Performance of robust PID and Q-design controllers for propofol anesthesia

Abstract

Control of propofol anesthesia is characterized by large variability in individual responses to drug infusion, relatively simple system dynamics and relatively low performance criteria. Robust PID control can be expected to provide adequate control given these characteristics. While feasibility of robust PID control of propofol anesthesia has been shown in clinical trials, controllers that use an explicit model might provide additional valuable characteristics. This paper examines the performance achieved with a manually tuned robust PID controller and a higher-order Q-design controller. The additional degrees of freedom in the Q-design allow an increase in the robustness margin, at the cost of decreased gain at low frequencies and corresponding increased time to induction of anesthesia. These results indicate that the uncertainty introduced by interpatient variability is an important factor limiting closed-loop performance. Performance improvement from increased controller complexity may therefore be limited, unless strategies aimed at reducing the uncertainty are implemented.