Single-center studies, which were retrospective and/or involved unblinded colonoscopists, have suggested that water exchange, but not water immersion, compared with air insufflation significantly increases the adenoma detection rate (ADR), particularly in the proximal and right colon. Head-to-head comparison of the three techniques with ADR as primary outcome and blinded colonoscopists has not been reported to date. In a randomized controlled trial with blinded colonoscopists, we aimed to evaluate the impact of the three insertion techniques on ADR. A total of 1224 patients aged 50 - 70 years (672 males) and undergoing screening colonoscopy were randomized 1:1:1 to water exchange, water immersion, or air insufflation. Split-dose bowel preparation was adopted to optimize colon cleansing. After the cecum had been reached, a second colonoscopist who was blinded to the insertion technique performed the withdrawal. The primary outcome was overall ADR according to the three insertion techniques (water exchange, water immersion, and air insufflation). Secondary outcomes were other pertinent overall and right colon procedure-related measures. Baseline characteristics of the three groups were comparable. Compared with air insufflation, water exchange achieved a significantly higher overall ADR (49.3 %, 95 % confidence interval [CI] 44.3 % - 54.2 % vs. 40.4 % 95 %CI 35.6 % - 45.3 %; = 0.03); water exchange showed comparable overall ADR vs. water immersion (43.4 %, 95 %CI 38.5 % - 48.3 %; = 0.28). In the right colon, water exchange achieved a higher ADR than air insufflation (24.0 %, 95 %CI 20.0 % - 28.5 % vs. 16.9 %, 95 %CI 13.4 % - 20.9 %; = 0.04) and a higher advanced ADR (6.1 %, 95 %CI 4.0 % - 9.0 % vs. 2.5 %, 95 %CI 1.2 % - 4.6 %; = 0.03). Compared with air insufflation, the mean number of adenomas per procedure was significantly higher with water exchange ( = 0.04). Water exchange achieved the highest cleanliness scores (overall and in the right colon). These variables were comparable between water immersion and air insufflation. The design with blinded observers strengthens the validity of the observation that water exchange, but not water immersion, can achieve significantly higher adenoma detection than air insufflation. Based on this evidence, the use of water exchange should be encouraged.Trial registered at ClinicalTrials.gov (NCT02041507).

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WE significantly increases overall ADR, ADR in screening cases, and in the right side of the colon; it also improves colon cleanliness but requires a longer insertion time.

The current results confirmed that water exchange minimized the requirement for sedation and increased the ADR.

The current review will attempt to describe the important lessons learned from published randomized controlled trials (RCT) comparing water immersion (WI) or water exchange (WE) techniques with gas insufflation colonoscopy. Air insufflation (AI) to distend the colon to permit visualization and passage through the lumen was developed for diagnostic colonoscopy. When screening colonoscopy was adopted, the same AI method was used. Interval cancers, diagnosed within 3 to 5 years after an index screening colonoscopy, appeared to be linked to low adenoma detection rate (ADR). Conscious sedation was introduced to manage insertion pain a few decades ago, incurring moderate costs of nursing staff, space for recovery, patient burdens of escort requirement, and at home recovery time. Recent advancement to deep sedation entailed additional costs of anesthesia staff support. In the past decade, investigators worldwide evaluated the use of water-assisted methods as an adjunct or in lieu of gas insufflation during insertion to minimize discomfort and improve ease of insertion. For convenience, one approach embraced the removal of infused water during withdrawal (WI). A subsequent evolution entailed removal of infused water predominantly during insertion (WE), specifically designed to further minimize insertion pain. Results of RCT shed light on the impact of WI and WE on insertion pain (primary outcome) and adenoma detection (secondary outcome). Water immersion is easier to learn and apply than WE, but mastery of the WE technique appears to have two major advantages. Current RCT data suggest that both WI and WE decrease insertion pain and facilitate completion of difficult colonoscopy, with WE having a superior impact than WI. Water exchange was serendipitously associated with an increase in ADR; this has been repeatedly confirmed in follow-up studies. When it is unknown which patient's colonoscopy will be difficult, it would seem prudent for the average colonoscopist to optimize the chance of success and increase in ADR by using WE from the very start.

Underwater polypectomy can be efficaciously used in routine clinical practice for the complete resection of colon polyps, with several advantages over gas insufflation polypectomy.

UEMR is an effective, safe and well tolerated option for significant colorectal polyps. Piecemeal resection, recurrent polyp, female gender, and difficult access are predictors of post-UEMR polyp recurrence.