Water exchange versus carbon dioxide insufflation in unsedated colonoscopy: less is more

We congratulate Garborg et al. [1] for their recent multicenter, randomized, controlled study comparing water exchange with carbon dioxide (CO₂) insufflation in unsedated colonoscopy. The primary end point of the study was the proportion of patients reporting moderate or severe pain at discharge. Regrettably, the study was not able to establish a statistically significant outcome with regard to the primary end point. We would like to raise the following points about the study.

It is well known that pain during insertion of the colonoscope is a major factor influencing cecal intubation time, hence the need for sedation and analgesia during colonoscopy. However, intraprocedural pain was only a secondary end point in this study. The authors have quoted the meta-analysis by Wu et al. [2] to demonstrate the superiority of CO₂ in reducing post-procedural pain. However, the same meta-analysis also showed a significant reduction in abdominal pain during the procedure (relative risk [RR] 0.77, 95 % confidence interval [CI] 0.62 – 0.96). In the same meta-analysis, the relative reduction in abdominal pain during the procedure was much more than the relative reduction in pain post-procedure, which was also significant [RR 0.26, 95 %CI 0.16 – 0.43]. Another randomized controlled study by Cadoni et al. [3] demonstrated that intraprocedural pain during cecal intubation was significantly reduced in the water exchange group compared with the air insufflation and water immersion groups.

Is pain at discharge a reliable measure of discomfort experienced during colonoscopy? We feel that recording pain at the end of the procedure introduced bias into the study. The ability of patients to recall their experience of an unpleasant medical procedure is susceptible to bias. The study by Redelmeier et al. [4], which demonstrated that the patient’s experience of colonoscopy can be altered by extending the period in which the colonoscope remains in the rectum, supports our argument. Garborg et al. mention in their discussion that the evaluation of pain during the procedure is not standardized. Is this the reason for choosing post-procedure pain as the primary outcome?

We would also like to draw attention to the use of the 4-point verbal rating scale (VRS-4), which is a categorical scale for recording pain. The authors quote the use of this scoring system in the Norwegian Gastronet project [5], where it was used to record intraprocedural pain. We would like to highlight the fact that the VRS-4 scale lacks ratio properties [6], and therefore its ability to draw conclusions on the magnitude of pain between different levels is diminished. This problem could have been avoided by using a numerical rating scale [3] or a visual analog scale. Yet another fact that may influence the use of sedation and patient experience of colonoscopy is the patient’s previous experience of colonoscopy. Previous colonoscopy was not an exclusion criterion in the Garborg study, and this could therefore have been a source of bias.

We look forward to the authors’ response to the points raised in this letter, and hope that it generates an enlightening discussion on the subject. No doubt this landmark study sets a new trend of “less is better and safer” sedation, that will influence the perception and practice of colonoscopy.

• References

• 1 Garborg K, Kaminski MF, Lindenburger W et al. Water exchange versus carbon dioxide insufflation in unsedated colonoscopy: a multicenter randomized controlled trial. Endoscopy 2015; 47: 192-199
• 2 Wu J, Hu B. The role of carbon dioxide insufflation in colonoscopy: a systematic review and meta-analysis. Endoscopy 2012; 44: 128-136
• 3 Cadoni S, Sanna S, Gallittu P et al. A randomized, controlled trial comparing real-time insertion pain during colonoscopy confirmed water exchange to be superior to water immersion in enhancing patient comfort. Gastrointest Endosc 2015; 81: 557-566
• 4 Redelmeier DA, Katz J, Kahneman D. Memories of colonoscopy: a randomized trial. Pain 2003; 104: 187-194
• 5 Hoff G, Bretthauer M, Huppertz-Hauss G et al. The Norwegian Gastronet project: continuous quality improvement of colonoscopy in 14 Norwegian centres. Scand J Gastroenterol 2006; 41: 481-487
• 6 Price DD, Bush FM, Long S et al. A comparison of pain measurement characteristics of mechanical visual analogue and simple numerical rating scales. Pain 1994; 56: 217-226