Colonoscopy insertion pain: water exchange vs water immersion
Water immersion (WI) and water exchange (WE) entail infusion of water to distend the lumen during the insertion phase of colonoscopy. In WI, water is an adjunct to air insufflation (AI) to facilitate insertion to the cecum, with removal of infused water predominantly during withdrawal. WE entails complete exclusion of air insufflation, suction of infused water, residual colonic air, and feces predominantly during insertion to minimize distention. Separate randomized controlled trials, systematic reviews, and meta-analysis have shown WE and WI to significantly reduce pain compared with AI, but there were no head-to-head comparisons. We made such direct comparison and tested the hypotheses that WE and WI, compared to AI, would reduce pain during the insertion phase of colonoscopy and that WE would have the lowest pain score.
We chose real-time unblinded maximum insertion pain score as a primary outcome, minimizing bias by investigators and adequately blinding patients. Real-time pain score has been shown to correlate significantly with Visual Analogue Scales and blinded recalled pain at discharge. Pain score at discharge, usually chosen as primary outcome in colonoscopy pain studies, can be easily influenced by leaving the instrument in the rectum for a short interval at the end of the procedure.
WE achieved the lowest real-time insertion pain score, required fewer adjunct maneuvers, making for an easier procedure, and offered the best chance to perform a complete unsedated colonoscopy with no pain or only minor discomfort. WE outperformed WI and AI in minimizing pain and may provide a strategy to improve acceptance of unsedated colonoscopy by patients, potentially reducing sedation-related adverse events, patient burden, and institutional costs. Our study also confirmed that recalled pain can be manipulated.
Future colonoscopy pain studies should employ real-time insertion pain as primary outcome, in adequately blinded patients, with precautions to minimize bias by colonoscopists.