The Effect of Cap-assisted Water Exchange Colonoscopy on Straight Passage of the Colonoscope Through the Sigmoid Colon, Without Loop Formation

Inclusion Criteria: * aged 18-80 years * sedation colonoscopy Exclusion Criteria: * History of colorectal surgery * Clinical suspicion of, or pathologically confirmed, colorectal cancer * Presence of any "alarm" symptom or sign-hematochezia, melena, unexplained anemia or weight loss, palpable abdominal mass, or a positive digital rectal examination * Pregnancy or lactation * Known or suspected gastrointestinal obstruction * Diagnosed inflammatory bowel disease * Use of antiplatelet or anticoagulant therapy (e.g., aspirin, warfarin) within 7 days before colonoscopy or any documented coagulation disorder * Current enrolment in another clinical study or participation in any clinical trial within the previous 60 days * Requirement for emergency colonoscopy * Any other condition that, in the investigators' judgment, renders the patient unsuitable for inclusion in the study