We prospectively evaluated for polyp detection in the ascending colon a cohort of consecutive patients addressed (intended) for complete colonoscopy in Alexandra University Hospital, Athens, Greece for a predetermined period (June 2017-June 2018). All colonoscopies were performed under conscious sedation by using midazolam and/or propofol and continuous monitoring for vital signs. The type of endoscopes used were adult high definition, with variable stiffness, colonoscopes Olympus Evis Exera CF-H185 and 190. Insufflation was performed by means of a CO2 insufflator (OLYMPUS - UCR). An irrigation pump (OLYMPUS - OFP2) was used if needed, either for washing or for water exchange technique according to the endoscopist judgement. Oral sodium and potassium sulphate in combination (Eziclen®) or PEG solutions (Klean Prep® or Fortrans®) were used for bowel preparation which was measured by means of the Segmental Boston Bowel Preparation Scale. Inclusion criteria were as follows: Patients older than 18 years, with a complete colonoscopy, for CRC screening or post-polypectomy surveillance or diagnostic assessment. Exclusion criteria precluded patients with previous colectomy or an abdominal surgery in the last 6 months, patients with polyposis syndromes or inflammatory bowel diseases and if they were unfit for polypectomy or the polyp specimen was not retrieved for histology. The protocol of ascending colon examination encompassed 2 phases: A first phase (1) divided in Forward view (1a) videlicet insertion from the right flexure to the caecum followed by a second forward view (1b) namely withdrawal till the right flexure and reinsertion to the caecum maintaining the endoscope straight and a second phase (2, Retroflexion) with U-turn of the colonoscope in the caecum till the right flexure and then redressing to the forward view and reinsertion to the caecum.

Concerning endoscopy 2 seniors and 4 trainees participated in the study. All colonoscopies were performed with at least 2 operators, one senior and one trainee. The main investigator, the most experienced endoscopist in the department was present during all the procedures for the ascending colon examination (SM). Only 3 attempts were permitted for retroflexion achievement, performed by the main investigator if a younger trainee or senior gastroenterologist could not perform it. Polyps were mapped during both phases and were not removed until the end of the inspection. Polypectomy followed according to the previous mapping and all polyps were collected and sent for histological examination. The protocol of this non-interventional study as well as the informed consent for the patients were submitted and approved by the local ethical committee.

Adenoma detection rate (ADR) was defined as the number of colonoscopies in which one or more adenomas were detected, divided by the total number of colonoscopies. ADR in the ascending colon as the number of colonoscopies with at least one adenoma in the ascending colon divided by the total number of colonoscopies. Adenoma miss rate (AMR) of the ascending colon was defined as the number of additional adenomas in ascending colon detected by retroflexed view divided by the total adenomas in ascending colon detected with two forward and retroflexion views. The per-patient miss rate was calculated as the number of patients with additional adenomas detected on retroflexion divided by the total number of patients who underwent the examination.

Finally we evaluated two additional quality parameters in order to assess the contribution of retroflexion in adenoma detection: adenomas per colonoscopy (APC) calculated by dividing the number of detected adenomas by the total number of colonoscopies and adenomas per positive participant (APP) calculated by dividing the number of detected adenomas by the number of colonoscopies in which at least 1 adenoma was detected.