Remifentanil Effect on Burst Suppression Ratio

The goal of this clinical trial is to determine whether remifentanil has a facilitating effect on the generation of burst suppression by propofol in adult patients (18-60 years) candidates for elective surgery who require remifentanil and American Society of Anesthesiology (ASA) classification I or II. The main question it aims to answer are: • To determine whether remifentanil has a facilitating effect on the generation of burst suppression by propofol. Participants will undergo general anesthesia with remifentanil and propofol sequentially. After loss of consciousness, remifentanil will be adjusted to a medium or high concentration randomly and it will be determined at what concentration of propofol the burst suppressions are generated. Then, the concentrations of propofol that generate burst suppression associated with either a medium or high concentration of remifentanil will be compared.