Water exchange versus carbon dioxide insufflation in unsedated colonoscopy: a multicenter randomized controlled trial

Background and study aims: Compared with air insufflation, water exchange and carbon dioxide (CO 2 ) insufflation have been shown to reduce colonoscopy discomfort; however, head-to-head studies of the two methods are lacking. We aimed to compare water exchange and CO 2 insufflation directly with regard to pain during primary unsedated colonoscopy. Methods: Patients willing to undergo unsedated colonoscopy at three centers in Norway and Poland were randomized 1:1 to water exchange or CO 2 insufflation during colonoscope insertion. Patients were blinded to group allocation. The primary end point was the proportion of patients reporting moderate or severe procedural pain on a 4-point verbal rating scale (VRS-4) at discharge. Secondary outcomes included the proportion of patients reporting no pain on the VRS-4. Results: A total of 473 patients were randomized. A discharge pain questionnaire was completed by 226 of 234 patients (97 %) in the water exchange group versus 226 of 239 patients (95 %) in the CO 2 group ( P = 0.37). Moderate or severe pain was reported by 47 of 226 patients (21 %) in the water exchange group versus 60 of 226 patients (27 %) in the CO 2 group ( P = 0.15). No pain was reported by 100 of 226 patients (44 %) and 69 of 226 patients (31 %) in the water exchange and CO 2 groups, respectively ( P = 0.003). On-demand sedation was used in 15 patients (6 %) in each group ( P = 0.95). Conclusions: There was no significant reduction in moderate or severe pain in a comparison of water exchange with CO 2 insufflation. The secondary outcome of no pain was significantly more frequent in the water exchange group. Clinical trials registry number: NCT01633333.