Risk Factors for Inadequate Bowel Preparation in Patients With Chronic Constipation

Inclusion Criteria: * 18-90 * Patients undergoing colonoscopy; * Patients meeting the criteria of chronic constipation of Rome Ⅳ; Exclusion Criteria: * history of colorectal surgery; * known of suspected colonic stricture or obstructing tumour; * ulcerative colitis; * Crohn's disease; * irritable bowel syndrome; * toxic colitis or megacolon; * known or suspected bowel obstruction or perforation; * pregnancy or lactation; * unable to give informed consent; * haemodynamically unstable.