Post written by Joseph C. Anderson, MD, MHCDS, from the Department of Veterans Affairs Medical Center, White River Junction, Vermont, and the Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.

The purpose of this study was to compare water to standard CO2 as a medium to inspect the colonic mucosa for polyp detection.

Although water exchange may improve adenoma detection when compared to CO2, it is unclear whether water is a better medium to fill the lumen during withdrawal and visualize the mucosa. Total underwater (TUC) involves the use of water exchange with the air valve off during insertion followed by the inspection of the mucosa under water. Our goal was to use a tandem colonoscopy design to compare miss rates for TUC to standard CO2 for polyps and adenomas.

We found that TUC had an overall higher polyp and adenoma miss rate than colonoscopy performed with CO2, and TUC took longer to perform. In fact, for some outcomes we observed a decrease in adenoma detection when using water. We also observed that the insertion time was significantly longer in the TUC than in the CO2 arms. Thus, we observed a longer procedure time with no benefit in adenoma miss rate. Our data suggest that water filling of the lumen during withdrawal, after water exchange during insertion, does not consistently increase adenoma detection and is not associated with a lower miss rate. Given the variation between endoscopists in this study with regard to detection with TUC, we recommend that others perform controlled trials of water exchange followed by water filling during withdrawal for its effect on detection.

One problem that we noted was that small white mucus particles were often suspended in the water during withdrawal, requiring ongoing and often time-consuming water exchange during withdrawal. Perhaps body temperature water or saline would be associated with less stimulation of new mucus production during TUC. Alternatively, inclusion of mucolytic agent in the water infusion might prevent this problem. We recommend that investigations to address how to prevent stimulation of new mucus production by water infusion be specifically undertaken.

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