Patients who undergo painless colonoscopy from May 1, 2019 to December 30, 2019.Inclusion Criteria: Age 18 years; ASA grade I - III level; Obtain informed consent. Exclusion Criteria:Age < 18 years; Allergic to the medicine used; Poor control of hypertension; Patients with hypovolemic or hypotension (systolic blood pressure < 80mmHg, or mean arterial pressure < 50mmHg); Severe sinus bradycardia (HR < 50 times/min) or atrioventricular block; Severe limited left ventricular function (EF<30%); Impaired renal function (GFR< 15ml/min) or requiring dialysis; Impaired liver function or drug abuse; Withdrawal criteria: patients required to withdraw. After inclusion, patients will be randomized to two groups: Propofol group: propofol is used as a sedative strategy: 2-5 mg/kg.h propofol during the whole colonoscopy; Dexmedetomidine group: Dexmedetomidine as a sedative strategy: 0.1mcg/kg continuous infusion for 15min, 0.7-1mcg/kg.h during the whole colonoscopy. The primary outcomes: 1. Patient's comfort score; 2. the incidence of adverse events. The secondary outcomes: 1. Patient's pain score; 2. Satisfaction score of endoscopists. This study aims to investigate whether dexmedetomidine is effectively and safely in Painless Colonoscopy, and improve the comfortable and safety of Painless Colonoscopy.
50 patients who undergo painless colonoscopy from May 1, 2019 to December 30, 2019 will be randomized to two groups: Propofol group: propofol is used as a sedative strategy; Dexmedetomidine group: Dexmedetomidine as a sedative strategy. Compared of comfort and pain score of patients, the occurrence of adverse events and the satisfaction score of endoscopists between two groups. This study aims to investigate whether dexmedetomidine is effectively and safely in Painless Colonoscopy, and improve the comfortable and safety of Painless Colonoscopy.