The goal of this trial is to evaluate whether water exchange colonoscopy and CO2-insufflation colonoscopy with an abdominal compression device (Maxbelt me3 type, Nippon Sigmax Co., Tokyo, Japan) can achieve a significantly lower proportion of patients requiring manual abdominal pressure during colonoscopic insertion compared with CO2 insufflation alone.

This will be a three-arm multicenter parallel randomized controlled trial (RCT) designed to compare the frequency of ancillary manual assistance (abdominal pressure and/or position change) between CO2-insufflation colonoscopy with Maxbelt (intervention group), CO2-insufflation colonoscopy with sham device (sham control group), and water exchange (WE) colonoscopy (WE group). Enrolled patients will be randomized in a 1:1:1 ratio to either the intervention, sham control, or WE group. This will be a comparison of three different methods (CO2 with interventional device, CO2 with sham device, WE) to see which one is better at decreasing the need for manual assistance by endoscopy staff during colonoscopic insertion.

This study will be conducted in two hospitals in Taiwan: Evergreen General Hospital at Taoyuan and E-Da Dachange Hospital at Kaohsiung. The Sepulveda Ambulatory Care Center, VAGLAHS, UCLA in the USA will be a non-recruiting participating site. This planned RCT will span 30 months (from June 2024 to November 2026), including 3 months for the initial setup and 3 months for the final analysis. The study site possesses state-of-the-art colonoscopy equipment setups, and the investigators are WE colonoscopy research experts.

Patients aged 45-75 y/o at average risk of colorectal cancer who are willing to participate will sign an informed consent before starting the colonoscopy procedure. Separate parallel randomization will be set up at each site, stratified by investigator and type of colonoscopy (screening, surveillance, or positive fecal immunochemical test result). Mode of sedation will include conscious sedation (fentanyl plus midazolam) or full sedation (propofol with fentanyl plus midazolam) . Randomization will be carried out by computer-generated sequences using a block design (four participants per block).

CO2 with interventional device group: The Maxbelt will be applied around the circumference of the lower abdomen just below the umbilicus based on patient's abdominal circumference. Five sizes of Maxbelt will be employed in this study: XS-size for 55-65 cm circumference, S-size for 65-75 cm circumference, M-size for 75-85 cm circumference, L-size for 85-95 cm circumference, and XL-size for 95-105 cm circumference. Once applied, participants will be asked to assess and confirm that the belt is fastened tightly but not uncomfortably.

CO2 with sham device group: A two-size larger Maxbelt with loose fitting will be used as a sham device: L-size will be used for 55-71 cm circumference, XL-size will be used for 72-88 cm circumference, and 2 XL-size will be used for 89-105 cm circumference.

WE group: The air pump will be turned off during the insertion phase of colonoscopy, while the colon is irrigated with warm-to-touch distilled water or half normal saline using a flushing pump. The WE approach involves the simultaneous infusion of water to facilitate luminal expansion and suction of unclean water during insertion.

Inclusion Criteria:

• Patients aged 45-80 years having an average risk for colorectal cancer who plan to undergo sedated outpatient colonoscopy for screening, surveillance, and those who have received a positive fecal immunochemical test result

Exclusion Criteria:

• Patients with hereditary colorectal cancer syndrome, including familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer (Lynch syndrome)
• Patients with serrated polyposis syndrome
• Patients with known or suspected inflammatory bowel disease
• Patients with a history of colorectal cancer or other intra-abdominal malignancy
• Patients with a history of colorectal resection
• Patients with a history of abdominal aortic aneurysm, cirrhosis, ascites, or other severe comorbid illnesses
• Patients with recent wounds or skin rash on the anterior abdominal wall and back
• Patients with known ventral hernia
• Patients with unsedated procedure
• Patients with planned bidirectional endoscopy
• Patients with body mass index >35 kg/m2
• Patients with waist circumference <55 cm or >105 cm
• Patients with known or suspected gastroparesis
• Patients with planned therapeutic procedures (e.g., hemostasis, removal of a large polyp)
• Patients with mental retardation
• Pregnant women or those planning pregnancy
• Patients unwilling to participate in the study