In all patients, standard monitors, and state and response entropy (SE and RE, respectively) based-depth of anesthesia will be applied. Normothermia will be maintained by using forced-air warming blankets. Anesthetic technique will be standardized in all studied patients. Anesthesiologists who give the anesthetic will be not involved in the collection of outcome data. General anesthesia will be induced with propofol (2-3 mg kg-1) and fentanyl (2-3 µg kg-1) to achieve a SE value less than 50 and the difference between RE and SE less than 10.