Although colonoscopy is currently regarded as the gold standard to detect and prevent colorectal cancer (CRC) but post-colonoscopy CRCs (interval cancer, IC) still occur. Recent studies demonstrated that protection by colonoscopy against right-sided colon cancer was lower than that attained in the left colon. Adenoma detection rate (ADR) has been correlated with IC - each 1 % increase in ADR is associated with 3% decrease in the risk of ICs. Hopefully, innovations that improve right colon ADR would reduce the right colon IC. Insertion water exchange (WE), characterized by infusing water to guide the advance of the colonoscope in an airless lumen with its removal mainly during insertion. WE has been shown to improve the overall and right colon ADR compared to traditional air insufflation (Air). Several plausible causes have been proposed to explain the enhanced ADR by WE, including decreased multitasking related distraction, improved bowel cleanness, and flat polyps appearing less flatten and floating up in water Therefore, the adoption of WE in the right colon might be especially beneficial. In addition, WE has been criticized for prolonged insertion time, about 3-5 minutes longer than Air to reach the cecum and required a learning curve of about 50 to 100 cases.In this study, we devise a right colon WE method (RCWE), in which Air will be used to intubate to the hepatic flexure, followed by WE in the right colon. We test the hypothesis that RCWE would increase the right colon ADR without prolonging the insertion time. Consecutive patients undergoing screening, surveillance, or diagnostic examinations performed by participating endoscopists will be stratified for enrollment. Patients will be randomized in a 1:1 ratio (n=207 per group) to either the AI or RCWE group. Demographic data (age, gender, height, and weight), indications for colonoscopy, history of abdominal or pelvic surgery, constipation and chronic use of laxatives will be ascertained before colonoscopy. Quality of bowel preparation, cecal intubation time, withdrawal time, total procedure time, use of abdominal compression, need for change of position, presence and location of polyps and reasons for incomplete colonoscopy will be recorded. In addition, the right colon (from the hepatic flexure to cecum) insertion time and withdrawal time and infused and suction water amount will be recorded separately.

Inclusion Criteria:

• Adults aged 40 to 80 years.
• Patients undergoing screening, surveillance, or diagnostic colonoscopy.
• Colonoscopy performed by participating endoscopists.
• Ability to provide written informed consent.

Exclusion Criteria:

• Inability or unwillingness to provide informed consent.
• Age < 40 years or > 80 years.
• History of colorectal surgery (e.g., partial colectomy).
• Known or suspected colorectal cancer.
• Known inflammatory bowel disease (e.g., ulcerative colitis or Crohn's disease).
• Planned therapeutic colonoscopy (e.g., polypectomy).
• Inadequate bowel preparation.
• Known or suspected colonic obstruction or severe stricture.
• Massive ascites.
• Severe comorbid conditions (e.g., renal failure).
• Emergency colonoscopy.