The quest for real time propofol monitoring: a review

Propofol-based total intravenous anaesthesia (TIVA) is being increasingly used for maintenance of general anaesthesia due to benefits over volatile anaesthetic-based anaesthesia. An ongoing concern with the use of TIVA is the increased incidence of unintended awareness. The bispectral index (BIS) monitor has been proven to reduce the risk of awareness in relaxant general anaesthesia; however, it does not directly measure or ensure adequate anaesthesia delivery. Volatile anaesthetic delivery is confirmed by end-tidal gas monitoring; however, there is no comparable monitoring in TIVA. Recent research has thus focused on the development of technologies supporting the real-time monitoring of propofol levels, which could allow TIVA to operate with the same direct feedback that end-tidal monitoring provides for the volatile anaesthetics. It would not replace pharmacodynamic effect monitoring such as BIS, as inter-patient variability in anaesthesia doses required for an adequate depth of anaesthesia remains. It could, however, complement it, allowing TIVA to operate with the same level of real-time monitoring, and overall risk of awareness, as volatiles. There are currently no technologies for this in use in the clinical setting. This review provides an overview of the various propofol measuring technologies that have been or are being developed, as well as some of the key ongoing attempts at applying these technologies in clinical settings. We discuss challenges that have impeded the implementation of promising innovations, and outline future directions for making real-time propofol monitoring a clinical reality.