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

Endoscopy. 2015 Mar;47(3):192-9. doi: 10.1055/s-0034-1390795. Epub 2014 Nov 20.


Background and study aims: Compared with air insufflation, water exchange and carbon dioxide (CO2) 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 CO2 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 CO2 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 CO2 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 CO2 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 CO2 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 CO2 insufflation. The secondary outcome of no pain was significantly more frequent in the water exchange group. Clinical trials registry number: NCT01633333.

Publication types

  • Comparative Study
  • Multicenter Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Abdominal Pain / etiology*
  • Abdominal Pain / prevention & control
  • Carbon Dioxide*
  • Cecum
  • Colonic Polyps / diagnosis
  • Colonoscopy / adverse effects
  • Colonoscopy / methods*
  • Female
  • Humans
  • Hypnotics and Sedatives / administration & dosage
  • Insufflation / methods*
  • Intubation, Gastrointestinal
  • Male
  • Middle Aged
  • Single-Blind Method
  • Water*


  • Hypnotics and Sedatives
  • Water
  • Carbon Dioxide

Associated data

  • ClinicalTrials.gov/NCT01633333