In minimally sedated Asian patients in a community setting the investigators showed that a limited volume of water infusion instead of air insufflation in either the rectal sigmoid colon or the whole colon significantly reduced pain score during colonoscopy. Cecal intubation rate was not compromised. The reduction of pain score ranges from 25% to 32 % in our previous studies.1, 2 In contrast, several US reports described the successful use larger volumes of water infused throughout the entire colon in patients undergoing colonoscopy which result in a greater reduction of the pain score, averaging about 56%.3-5 A recent review suggested that the cause of the difference might lies in the timing of water removal.6 Specifically, the investigators group removed the infused water predominantly during withdrawal phase (water immersion) and the U.S. group removed water during insertion phase (water exchange).

This prospective, randomized controlled trial compared water exchange or water immersion with traditional air insufflation in patients undergoing minimally sedated colonoscopy. The investigators test the hypothesis that water exchange can reduce more pain than water immersion in the investigators clinical setting.

All procedures will be recorded and stored as digital files.

Inclusion Criteria:

• Patients undergoing minimally sedated colonoscopy

Exclusion Criteria:

• Obstructive lesions of the colon, inadequate bowel preparation, allergy to meperidine, massive ascites, past history of partial colectomy, or refusal to provide written informed consent.

patients underwent endoscopy by YHH

Single center; single endoscopist