Pharmacokinetic-Pharmacodynamic Modelling of Sevoflurane

Patients will be given information and consented. Patients will have arterial line inserted prior to induction. BIS monitoring will be applied prior to induction. Induction of anaesthesia will be done by gaseous induction with sevoflurane as it is a well recognised option for induction. Amount of sevoflurane given to patient will be dictated by the level of anaesthesia required for each patient as it is a normal anaesthetic practice. Normally sevoflurane will be to achieve MAC (Minimal alveolar concentration) of 0.8~1.2. Analgesia will be provided using remifentanil infusion. During the process of the induction, maintenance and emergence of anaesthesia, serial arterial blood samples will be taken at varying intervals. one prior to induction, at 2 min, 4 min, 8 min, 16 min, 32 min and every 15~30 min thereafter. The total volume of blood withdrawn would be about 30mL which would be around 1% of blood volume. These samples will be analysed for arterial concentration of sevoflurane. Other data related this study are automatically collected by comupter recording system of anaesthetic machine. This is a normal part of our anaesthetic practice. Along the anaesthetic process, Bispectral monitoring data will be collected and recorded onto our anaesthetic computer recording system. This will be used to analyse pharmacodynamic aspect of sevoflurane. This is a routine anaesthetic practice.