Water exchange method has been shown to reduce medication requirement and pain experienced during colonoscopy. It may increase the adenoma detection rate (ADR). Water exchange provides salvage cleansing and the refractive index of water (n equals about 1.3) is larger than that of air, which creates optical distortion that likely contributes to objects appearing larger underwater, making smaller lesions easier to visualize and it may help draw attention to those smaller lesions during withdraw. These principles facilitate to the higher adenoma detection rate.

There is a large number of literature on the adenoma detection rate during water exchange colonoscopy, but most studies have been conducted in only one centre, simple-size, and under sedation patients, the influence of adenoma detection rate under unsedation patients was unclear.

The aim of this study is to compare the ADR of colonoscopy by using the water exchange method versus the conventional air method in unsedation patients in multiple centers in China.

Inclusion Criteria:

• age 18-80 patients with intact colon and rectum

Exclusion Criteria:

• prior finding of severe colorectal stricture;
• solid fetus contained in the last stool before colonoscopy
• no bowel preparation or cleansed by enema/lavage
• without the requirement of reaching cecum
• known colorectal polyps or polyposis syndrome without complete removal previously
• pregnant women
• hemodynamically unstable
• patients who cannot give informed consent