Safety, constraints and anti-windup in closed-loop anesthesia

Feasibility of closed-loop anesthesia has been shown in a number of clinical studies. Demonstration of patient safety will be essential to convince regulatory authorities of the benefits of such systems. This paper considers safety constraints for closed-loop propofol anesthesia based on its therapeutic range. Simulation scenarios are proposed for evaluation of control strategies in the presence of these constraints. The scenarios reproduce realistic situations encountered in clinical practice. Using the proposed scenarios, the performance of L2 anti-windup is compared to sliding mode reference conditioning and to back-calculation anti-windup. It is concluded that L2 anti-windup might not be appropriate for this problem. The sliding mode solution results in behaviour comparable to the Hanus conditioned controller and there seems to be no need for fast switching. The back-calculation anti-windup performs well in a variety of situations.