Blood Propofol Measurement During Anaesthesia Using Propofol Target Controlled Infusion

Propofol is a commonly used agent for sedation and anaesthesia in the intensive care unit and the operating room. The pharmacokinetics of propofol are difficult to predict in patients not conforming to the norms in which the original pharmacokinetic research was based. Such patients, including the critically ill, and morbidly obese, are increasingly being encountered. The investigators group have been involved in the development of a device which can measure blood propofol concentrations, and hope for this to be available to use in the operating room in a clinically useful timeframe in the future. Data will be collected on patients undergoing propofol based general anaesthesia. The Marsh target controlled algorithm in effect site mode (commonly used by anaesthetists) will be assessed for accuracy using the propofol monitor. A new proportional correction method will be developed using this data, designed to enable recalibration of the TCI algorithm in near real time in order to achieve a more accurate estimated propofol concentration in these identified patient groups. The research will investigate the effectiveness of a correction of estimated propofol levels based on a one off measurement early on in the anaesthetic, and will take subsequent samples to measure propofol levels without modifying the TCI algorithm. Additionally, data on anaesthetist choice of TCI model, and method of administration in this relatively unselected group of patients will be analysed.