Modelling propofol pharmacodynamics using BIS-guided anaesthesia.

Using Schnider's pharmacokinetic model, propofol pharmacodynamics were modelled during total intravenous anaesthesia. The method involved adjusting a pharmacokinetic/pharmacodynamic model according to data obtained from 42 patients having operative procedures with remifentanil analgesia. Parameters Ce50 and γ were estimated for induction and maintenance by analysing patients' bispectral index. The pharmacodynamic models were different for induction and maintenance. The mean (95% CI) Ce50 for induction and maintenance was Ce50 = 3.35 (2.79-3.91) mg.l(-1) and 2.23 (1.95-2.51) mg.l(-1) , respectively, with a higher concentration required to achieve the same effect during induction, even during remifentanil co-administration. During induction and maintenance, γ was 1.24 (1.44-2.00) and 1.58 (1.32-1.84), respectively. As γ is related to the concentration-effect slope, patient response is accentuated during maintenance compared with induction. The influence of sex and age on the model was analysed. Sex had no significant influence on the model, although a linear relation was found between age and Ce50 .