Validation of a Pharmacokinetic Pharmacodynamic Model to Administer Propofol in Obese Patients

General anesthesia will be induced administering propofol by effect site TCI system using our previously derived model, the target plasma concentration initially will be set at 4 mcg/ml. After loss of consciousness, rocuronium 0.6mg/kg, and remifentanil 0.2mcg/kg/min will be given to facilitate tracheal intubation. After intubation propofol target will be decreased to 3 for 10 minutes and then adapted to the needs of each patient to maintain stable BIS values between 40 and 50. At the end of surgery propofol infusion will be stopped, and patients will be transferred to the recovery unit extubated. Samples of 2.5 ml of arterial blood will be taken at 2, 5 and 10 min after every new target is set. Thereafter samples will be taken at 2, 5, 10, 15, 30, 60, 120 min after stopping drug infusion. Blood samples will be immediately centrifuged and then stored until analysis.