Low adenoma detection rate (ADR, proportion of patients with at least one adenoma found in the colon) is correlated with the risk of post-colonoscopy colorectal cancer (CRC). Air insufflation (AI) colonoscopy has been reported to fail to prevent some post-screening right-sided CRC incidence and mortality. Small flat polyps containing advanced histology, more likely to be missed during colonoscopy, are more common in the proximal and in the right colon.
Water-aided colonoscopy entails the infusion of water in lieu of gas insufflation to distend the lumen during the insertion phase. In water immersion (WI), water is infused to facilitate cecal intubation, with limited use of insufflation when necessary. Opaque water is removed as needed to aid progression without maximising cleanliness. Residual air pockets are used to bypass dirty content. Infused water is removed predominantly during withdrawal. Water exchange (WE), modified from WI, entails gasless insertion in clear water, minimising distention and maximising cleanliness. Infused water is removed predominantly during insertion. With both techniques withdrawal is carried out using insufflation as usual.
Compared with AI, the impact of WI and WE differs. WI has not been found to significantly increase ADR. On the contrary, previous studies have suggested that WE might increase ADR, particularly for small size lesions in the proximal colon, providing salvage cleansing and improving bowel preparation. The limitations of these studies were their retrospective analysis, colonoscopists that were unblinded to the insertion method, and the lack of a direct comparison of WE, WI, and AI, with ADR as the primary outcome.
In a head-to-head comparison of the three techniques with blinded colonoscopists, we tested the hypothesis that WE would achieve the highest ADR, with a significant improvement compared with AI. The primary outcome was ADR. Secondary outcomes were right colon ADR, advanced ADR, and total and segmental Boston Bowel Preparation Scale (BBPS) scores.
We conducted a randomised controlled trial at three community hospitals (two in Italy and one in the Czech Republic). From February 2014–March 2016, in an open access colonoscopy programme with sedation available, consecutive 50–70-year-old screening patients were enrolled and randomised 1:1:1 to WE, WI, and AI (n=408 in each group). Instructions on the split-dose bowel preparation were provided to all patients in a rigorous manner. After reaching the cecum, another colonoscopist blinded to the insertion technique performed the withdrawal.
Patients randomised to the water groups had the colon irrigated with water using flushing pumps. WE and WI were performed as described. In the AI group, colonoscopy was performed in the usual fashion. In all arms withdrawal lasted ≥6 minutes. Demographics, clinical features, and indications were comparable, as well as cecal intubation rates and procedure times.
Even after split-dose preparation, WE achieved the highest overall and right colon BBPS scores (versus WI and AI p<0.001). Compared with AI (40.4%), WE (49.3%, p=0.011), but not WI (43.4%, p=0.396), achieved significantly higher overall ADR, right colon ADR (WE: 24%, WI: 19.1%, AI: 16.9%; WE versus AI p=0.012), and advanced right colon ADR (WE: 6.1%, WI: 4.4%, AI: 2.5%; WE versus AI p=0.010). Uniquely, WE was associated with an increase in ADR from good to excellent cleanliness (p=0.007). In the right colon, at excellent segment cleanliness (BPPS=3) WE achieved significantly higher ADR for lesions both of any size and <10 mm (p=0.002), compared with AI.
In conclusion, the design with unbiased colonoscopists strengthens the validity of the observation that WE, but not WI, achieves a significantly higher ADR than AI. The effectiveness of screening colonoscopy hinges on the detection and removal of cancer precursors and early detection of CRCs. Novel approaches to increase ADR are desirable to decrease the incidence of post-colonoscopy CRC. This may be achieved using new technologies or different colonoscopy techniques. Our findings may be relevant in addressing the issue of missed adenomas, particularly in the right colon. The use of WE and further investigations of its impact should be encouraged.