As the investigators know, postoperative cognitive dysfunction (POCD) is a fairly well-documented clinical phenomenon, which affect patients' short-term and long-term outcome. Most patients will receive general anesthesia and cardiopulmonary bypass (CPB) during cardiac valvular surgery. Inhalation sevoflurane based and propofol based anesthesia are most commonly used strategy for general anesthesia. At present, it was unknown that which one is better in providing cerebral protection effect for patients undergoing cardiac valvular surgery with CPB. The current study aimed to explore the possible difference.