A Low Dose Dexmedetomidine in Sedation Colonoscopy

104 patients who undergo painless colonoscopy from January 20,2024 to February 29,2024 will be randomized to two groups: propofol group and dexmedetomidine group. In the dexmedetomidine group,dexmedetomidine is infusion intravenously with a loading dose of 0.5 μg kg-1 for 10 min, then infusion at 0.3 μg kg-1 h-1 according to the ideal body weight of the patient until the end of colonoscopy. In the propofol group, Propofol is administrated 1 mg kg-1 intravenously, then titrated given by 0.5 mg kg-1 during the whole process.