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.
Keywords: Adenoma detection; Colon cleanliness; Sedation; Water exchange; Water immersion; Water-aided colonoscopy.