The Bispectral Index (BIS) is an electroencephalogram-derived measure of anesthetic depth. A closed-loop anesthesia system can be built using BIS as the control variable, two proportional-integral-differential control algorithms, a propofol and a remifentanil target-controlled infusion systems as the control actuators. Preliminary results show that this system can be used during surgery. We propose a prospective randomized study to evaluate the effectiveness of such a closed-loop anesthesia system during the postoperative period. Two groups of patients are compared: one in which propofol and remifentanil are administered by the anesthesiologist using target-controlled infusion systems, and one in which propofol and remifentanil are administered automatically by the combined closed-loop anesthesia system. In both groups, the goal is to maintain BIS between 40 and 60, the recommended range during anesthesia by the manufacturer. We expect the combined closed-loop system group to do similar or better.