Development of a Pharmacodynamic Model for Propofol in Older Adults

The goal of this pharmacodynamic study is to develop a model for Propofol administration for older adults (\>65 years). The main objective is to create a model based on a new pharmacodynamic parameter, derived from frontal electroencephalogram (EEG), to admininster Propofol in older adults. With this new model, the investigators aim to: * Evaluate the relationship between the plasmatic concentration, described by the Eleveld pharmacokinetic model, versus the effect of the drug represented with a new parameter derived from the intraoperative frontal EEG. * To validate the predictive ability of Eleveld's pharmacokinetic-pharmacodynamic model, based on the bispectral index (BIS), compared to the new model based on a parameter derived from intraoperative frontal EEG. Participants will be asked to answer preoperative questionnaires, receive a Propofol intravenous infusion concomitantly with continuous BIS and EEG monitoring, and to be evaluated for clinical sings of loss and return of consciousness.