Randomised trial of ‘hybrid’ water-assisted colonoscopy (modified water immersion) versus water exchange colonoscopy: WAVE study

Background and aims Colonoscopy practice has evolved with a trend towards water-assisted insertion. A recent national survey suggests a hybrid approach to colonic distension during insertion, with water used predominately to the splenic flexure and carbon dioxide (CO 2 ) with water used thereafter to the caecum, is commonly used. This contrasts with the water exchange technique where no CO 2 is used. This study aimed to evaluate whether a hybrid or water exchange technique allows more efficient colonoscopy. Methods This prospective, randomised controlled trial was conducted between March 2021 and June 2022. Participants were randomised 1:1 to hybrid or water exchange colonoscopy, performed by four experienced colonoscopists. The primary outcome was total procedure time with secondary outcomes of caecal intubation time, caecal intubation rate, polyp detection, loop formation, number of ancillary manoeuvres, sedation use and patient comfort. Results 256 patients were invited, and 246 were randomised to either hybrid or water exchange colonoscopy. 122 patients were included in each arm of the primary analysis. Total procedure time was greater in the water exchange group compared with hybrid (29 vs 25 min, p=0.009). Patient reposition episodes occurred more frequently in the water exchange group vs hybrid group (5.5 vs 5, p=0.003) and left colon Boston Bowel Preparation Scale (BBPS) score was improved. No difference was seen in all other outcomes. Conclusion A hybrid technique, compared with water exchange, enabled faster colonoscopy without adversely impacting sedation requirement, caecal intubation, overall bowel cleansing and patient comfort. This technique appears to maximise the advantages of both water and CO 2 to enable more efficient colonoscopy. Trial registration number NCT04710706 .