Anaesthesia simulator: intelligent monitoring and control of depth of anaesthesia

Abstract

A system has been developed for monitoring the anaesthetic state of patients during surgical interventions under general anaesthesia using propofol for unconsciousness and fentanyl for analgesia. This subject has received much attention from the research community especially since the advent of balanced anaesthesia, which has made the detection of awareness much more difficult. Mid-Latency Auditory Evoked Potentials (MLAEPs) obtained during general anaesthesia are being used within the design of a neuro-fuzzy system for the determination of the level of unconsciousness after feature extraction using multiresolution wavelet analysis. A second measure for depth of anaesthesia is based on the cardiovascular system status, e.g. blood pressure and heart rate. The 2 measures are fused and a final depth of anaesthesia is assessed. Based on the classified Depth of Anaesthesia (DOA), a target concentration is decided by a rule-based fuzzy logic controller which feeds the set-point to a Target Controller Infusion algorithm (TCI) for maintaining automatic drug infusion. The patient is simulated using a 3 compartment mathematical model of the drug infusion and effect. The system provides a closed-loop architecture that can automatically provide the drug profile necessary to maintain the patient at a safe level of anaesthesia. Subsequently, the system can be used as an on-line advisory system (training simulator) designed for guidance on the target of propofol concentration to be used. This open-loop system includes the anaesthetist within the loop controlling the final target concentration for TCI system, thereby maintaining overall control over the system. Here, a patient simulator is described for use with DOA measurements and a control system. The simulator runs on a separate PC in order to provide a realistic simulation environment. The same system (including the patient simulator) is being implemented on a single laptop computer with a user interface capability (Windows based) which is used as a training simulator for anaesthetists.