ERCP is commonly done under sedation with midazolam and meperidine, however some studies showed varying outcomes of this conventional sedation for maintained sedation. Propofol is increasing used for sedation in gastrointestinal procedure owing to its rapid recovery profiles but the complications associated with propofol are not negligible.The investigators prospectively compare the efficacy, induction time, recovery time, patient satisfaction and side effect between propofol based and conventional sedations in patients undergoing ERCP.