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Original research
Randomised trial of ‘hybrid’ water-assisted colonoscopy (modified water immersion) versus water exchange colonoscopy: WAVE study
  1. Ahmir Ahmad1,2,
  2. Anna Buenaventura1,
  3. Belma Motes1,
  4. Ravi Misra1,2,
  5. Ripple Man1,
  6. Angad Dhillon3,
  7. Paul Bassett4,
  8. Kowshika Thiruvilangam1,
  9. Brian P Saunders1,2
  1. 1Wolfson Unit for Endoscopy, St Mark's Hospital and Academic Institute, London, UK
  2. 2Department of Surgery and Cancer, Imperial College London, London, UK
  3. 3Queen Elizabeth Hospital, Lewisham and Greenwich NHS Trust, London, UK
  4. 4Statsconsultancy, Amersham, UK
  1. Correspondence to Dr Ahmir Ahmad, Wolfson Unit for Endoscopy, St Mark's Hospital and Academic Institute, London HA1 3UJ, UK; ahmir.ahmad{at}


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 (CO2) with water used thereafter to the caecum, is commonly used. This contrasts with the water exchange technique where no CO2 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 CO2 to enable more efficient colonoscopy.

Trial registration number NCT04710706.


Data availability statement

All data relevant to the study are included in the article or uploaded as supplementary information.

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Data availability statement

All data relevant to the study are included in the article or uploaded as supplementary information.

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  • X @DrAhmirAhmad

  • Contributors AA and BPS conceived the idea and prepared the protocol. AA wrote the first draft. AA, AB, BM and RM, performed procedures. PB was the study statistician. KT was the dedicated research nurse. All authors had access to the study data, reviewed and approved the final manuscript. AA and BPS were involved in manuscript planning, editing and review and were responsible for overall content as guarantors.

  • Funding We are grateful for charitable funding administered through St Mark’s Hospital Foundation (funding reference RES256).

  • Competing interests AA: research funding and equipment loan from Olympus. BPS: received speaker fees, loan equipment and research funding from Olympus and received speaker fees and loan equipment from Fuji. All other authors have no conflicts to declare.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.