• Joseph C Anderson, Charles J Kahi, Andrew Sullivan, Margaret MacPhail, Jonathan Garcia, and Douglas K Rex.
• Department of Veterans Affairs Medical Center, White River Junction, Vermont, USA; The Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
• Gastrointest. Endosc. 2019 Mar 1; 89 (3): 591-598.

Background And AimsAlthough water exchange may improve adenoma detection compared with CO2, it is unclear whether water is a better medium to fill the lumen during withdrawal and visualize the mucosa. Total underwater colonoscopy (TUC) involves the use of water exchange with the air valve off during insertion followed by the inspection of the mucosa under water. Our goal was to compare miss rates for TUC with standard CO2 for polyps and adenomas using a tandem colonoscopy design.MethodsWe randomized participants to undergo tandem colonoscopies using TUC or CO2 first. In TUC, water exchange was performed during insertion, and withdrawal was performed under water. For the CO2 colonoscopy, both insertion and withdrawal were performed with CO2. The main outcomes were miss rates for polyps and adenomas for the first examination calculated as the number of additional polyps/adenomas detected during the second examination divided by the total number of polyps/adenomas detected for both examinations. Inspection times were calculated by subtracting the time for polypectomy, and care was taken to keep the times equal for both examinations.ResultsA total of 121 participants were randomized with 61 having CO2 first. The overall miss rate for polyps was higher for the TUC-first group (81/237; 34%) compared with the CO2-first cohort (57/264; 22%) (P = .002). In addition, the overall miss rate for all adenomas was higher for the TUC-first group (52/146; 36%) compared with the CO2 group (37/159; 23%) (P = .025). However, 1 of the 3 endoscopists had higher polyp/adenoma miss rates for CO2, but these were not statistically significant differences. The insertion time was longer for TUC than for CO2. After adjusting for times, participant characteristics, and bowel preparation, the miss rate for polyps was higher for TUC than for CO2.ConclusionsWe found that TUC had an overall higher polyp and adenoma miss rate than colonoscopy performed with CO2, and TUC took longer to perform. However, TUC may benefit some endoscopists, an issue that requires further study. (Clinical trial registration number: NCT03231917.).Copyright © 2019 American Society for Gastrointestinal Endoscopy. Published by Elsevier Inc. All rights reserved.

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