Water or saline? Exploring mucus production and polyp detection in water-assisted colonoscopy

In recent years there has been a growing body of evidence on water-assisted colonoscopy (WAC). Water exchange (WE) colonoscopy, one of the WAC techniques, has demonstrated higher intubation rate, higher adenoma detection rate (ADR), and reduced patient discomfort compared to gas insufflation colonoscopy. In our clinical practice, we have observed increased mucus production in the rectosigmoid segments during withdrawal when WAC techniques are used with water infusion compared to saline infusion. This white, opaque mucus often requires further mucosal lavage and removal, which can be time-consuming and could decrease polyp detection rates. Since low ADR is correlated with the risk of interval colorectal cancer (CRC), further attempts to improve ADR are needed. Two recent studies have explored this phenomenon. In 2020 Rahyel et al. reported higher mucus production with room-temperature water compared to saline infusion during colonoscopy insertion. In 2023 Cheng et al. randomized patients to colonoscopy with CO2 insufflation or WE colonoscopy with warm water, 25% saline or 50% saline. Mucus production was highest in the water group, followed by the 25% saline, 50% saline, and CO2 groups.