The study is performed in order to develop a population pharmacokinetic and pharmacodynamic model of Propofol in morbidly obese patients. A covariate analysis will be performed in order to account for variability in pharmacokinetic and pharmacodynamic parameters. The results will be used to develop individualised dosing schemes for Propofol in morbidly obese patients. This model will take into account patient and procedure bound covariates.