Monitoring the depth of anaesthesia using bispectral analysis and closed-loop controlled administration of propofol

The bispectral index, a univariate dimensionless parameter of depth of anaesthesia, correlates very well with clinical signs of anaesthesia and with hypnotic drug concentrations. Although still in the process of adjustment (several versions have been designed), it is currently one of the best anaesthetic depth indicators. In this chapter we discuss its relative merit versus other methods of assessing depth of anaesthesia. Since several studies have demonstrated its value, it is not surprising that several investigators have incorporated the bispectral index as a controlled variable in closed-loop feed-back control administration systems, especially for propofol. We discuss such systems and emphasize the importance of a model-based approach in the development of these devices.