Design: Prospective double blinded two-center randomized controlled trial. Methods: Colonoscopy with CO2 insufflation and water exchange-CO2, water exchange-AI; split-dose bowel preparation; on demand-sedation.
Control method: CO2 insufflation colonoscopy. Study methods: water exchange-CO2 colonoscopy, water exchange-AI colonoscopy.
Population: Consecutive 18 to 80 year-old first-time diagnostic outpatients. After informed consent, assignment to control or study arms based on computer generated randomization list with block allocation and stratification.
