We have developed and deployed within our operating rooms a system which provides real-time estimates of effectsite levels of inhalational anaesthetic agents along with forward predictions of end-tidal and effect-site concentrations. The initial aim of this project was to provide users of inhalational agents with tools similar to those available in target-controlled infusion systems. This paper describes the development and implementation of the system and outlines evaluation and uses of the system. The prototype was developed by combining a locally developed data logging and trend display system with a model of uptake developed as a teaching tool in 1982. This uptake model performs as well as contemporary models of propofol uptake and distribution. Following initial evaluation, the system has been deployed in over half our operating rooms and uses data gathered from the Datex/GE Anaesthesia Delivery Unit anaesthetic machines. We have conducted a number of studies of the system itself, explored aspects of the underlying models, and used the system to investigate effect-site guided anesthesia and as a tool for data collection in other studies. The system has been well accepted locally and has been shown to facilitate faster changes in inhalational levels. We have also seen a significant decrease in fresh gas flow rates over recent years and attribute this in part to the predictive system, which simplifies the task of determining the appropriate combination of gas flow and vapour dial setting. The system also provides a useful platform for a range of research projects.

We audited the total number of perioperative epidural techniques performed at Christchurch Hospital, New Zealand, for three years, before and after The Lancet published the MASTER Anaesthesia Trial in 2002. We also looked specifically at the number of epidural anaesthetic and analgesic techniques performed in combination with general anaesthesia for colonic surgery over the same period. In both cases we found a statistically significant fall in epidural rate in the years after the publication (P<0.001). A subsequent survey of local specialist anaesthetists, who have worked throughout this period, revealed the majority (75%) were knowingly performing fewer epidural techniques and that the findings of the MASTER Anaesthesia Trial had influenced their decisions.