Low air pressure insufflation during insertion phase of colonoscopy

Interventions: We use low pressure air insufflation instead of high pressure during insertion phase of colonoscopy. Air insufflation is usually needed during colonoscopy. There are 3 air pressure level of air pressures on the control panel: high, median and low. Traditionaly, high pressure (0.05 MPa) is used. In this study, we use low pressure (0.0075-0.015 MPa) during insertion phase of colonoscopy to minimize loop formation. Before the colonoscopy is started, the air pressure was switched to low level on the control panel. Primary outcome(s): to reduce cecal intubation time by one minute[At the end of colonoscopy] Study Design: Purpose: Diagnosis; Allocation: Randomised controlled trial; Masking: Open (masking not used);Assignment: Parallel