Water and carbon dioxide – turning back the clock to unsedated colonoscopy
25 February 2015 (online)
In recent years, we have seen a shift from moderate sedation toward deep sedation, even for routine procedures such as screening and surveillance colonoscopies . Sedation may minimize discomfort and allow an examination that is not compromised by patient movements. However, sedation also increases risk, is expensive, and requires a greater time commitment from the patient and the endoscopy team (including time for preprocedural evaluation and post-sedation care). In addition, a patient escort is needed.
Concern for patient discomfort and pain has justified the need for sedation. Procedural pain and discomfort are caused by stretching of the intestinal wall, especially during scope insertion with insufflation of the lumen. Both water-assisted colonoscopy and carbon dioxide (CO2) insufflation ease wall tension and reduce patient discomfort. Water-assisted colonoscopy involves the abundant infusion of water during insertion of the colonoscope (typically at least 500 mL), with the subsequent suctioning of water during the insertion phase (“water exchange colonoscopy”) or during withdrawal (“water immersion colonoscopy”). Water lubricates the scope – mucosa interface and allows a smoother passage of the scope. The air channel is turned off, resulting in less wall tension. Especially in the angulated sigmoid colon, water-assisted colonoscopy may ease insertion by shortening and straightening the colonic segment . Several studies have demonstrated a reduction in procedural discomfort with water-assisted colonoscopy in comparison with conventional air insufflation colonoscopy  .
CO2, which is increasingly used in many endoscopy centers, is readily absorbed after insufflation and so may cause less wall tension. CO2 insufflation has been shown to be associated with a decreased need for analgesic medications and less post-procedural discomfort in comparison with air insufflation   . Although both approaches seem beneficial, studies comparing the use of water-assisted colonoscopy with CO2 for unsedated colonoscopy are lacking.
In this edition of Endoscopy, Garborg et al. have compared water-assisted colonoscopy and CO2 colonoscopy without sedation in a randomized trial . At centers in Norway and Poland, 473 individuals who were willing to undergo unsedated colonoscopy were randomized to water exchange colonoscopy or CO2 colonoscopy. Sedation was provided for those participants requesting it during the procedure. The primary outcome was the proportion of participants who reported moderate or severe versus no or slight post-procedural pain at discharge, measured on a 4-point verbal rating scale.
The study found a small, nonsignificant difference between the post-procedural pain scores of the two groups, with fewer patients reporting moderate or severe pain following water-assisted colonoscopy (21 %) than following CO2 colonoscopy (27 %; P = 0.15). When secondary outcomes were considered, significantly more patients had no pain after water-assisted colonoscopy (44 %) than after CO2 colonoscopy (31 %; P = 0.003). Intraprocedural pain scores also favored water-assisted colonoscopy, with a lower median overall pain score (2.0 vs 2.4; P = 0.02) and a lower median maximum pain score (5.0 vs. 5.0; P = 0.006).
The study has several strengths. Pain was assessed twice, both during and after colonoscopy, lending more weight to the results. Unlike previous studies of water-assisted colonoscopy, this study enrolled equal numbers of men and women, allowing generalizable findings. In addition, the participants were blinded to the method of colonoscopy, decreasing the potential for bias. Finally, in contrast to other single-center studies, the current trial included six endoscopists at three centers.
As a potential limitation, the study may have been underpowered to show the 6 % absolute difference between the moderate and severe pain scores for water-assisted colonoscopy and those for CO2 colonoscopy (primary outcome) as significant. However, some may consider this difference small and not clinically relevant. Furthermore, the study enrolled only those patients who agreed to an examination without sedation. It is remarkable that fewer than 5 % of patients declined study participation because they preferred an examination with sedation. Thus, selection bias is of little concern, and the study cohort represents the majority of the screening and surveillance population at the participating sites.
For both groups, the median insertion times were longer than those reported in routine practice : 15 minutes for water-assisted colonoscopy and 11 minutes for CO2 colonoscopy. A longer insertion time likely reflects the endoscopist’s attempt to introduce the scope more carefully, with less force, to minimize discomfort. Long insertion times for water-assisted endoscopy have also been reported in previous studies , raising concerns about the efficiency of endoscopy and potentially negating any benefit gained from not using sedation.
Although the current study suggests that water is slightly superior to CO2 for unsedated colonoscopy, both aid unsedated procedures. In clinical practice, if unsedated colonoscopy is the goal, it therefore seems to make sense to use a combination of insufflation with CO2 (which is already the standard insufflation gas in many endoscopy units) and water assistance. In this trial, the intention-to-treat cecal intubation rate was higher in the CO2 group, but both rates fell short of the recommended 95 % . However, the clinically important overall cecal intubation rate was higher for the group in which water was aided by CO2 than for the group in which CO2 was used alone (97 % vs 92 %). Thus, a hybrid approach may achieve superior intubation rates in unsedated examinations.
From a broader perspective, this well-executed study adds to the growing number of publications that support the adoption of techniques such as CO2 colonoscopy or water-assisted colonoscopy to achieve excellent outcomes of unsedated endoscopy for routine procedures    . The current and previous studies should inspire us to reflect on our current practice. Endoscopists are increasingly using deep sedation with propofol, which provides a seemingly zero-awareness experience for the patient – something that we believe many patients want. It is interesting to note that more than 20 % of the patients in this study reported moderate or severe pain, yet only 6 % of the patients requested sedation. Thus, most patients in the study accepted some level of discomfort. Our expectation and uneasiness as endoscopists dealing with patients experiencing procedural discomfort may affect the level of sedation we provide as much as our patients’ expectations. Instead of adjusting our techniques to minimize discomfort, possibly prolonging insertion time, we may choose to increase the level of sedation for the sake of ease and efficiency. The majority of participants in both groups tolerated colonoscopy without sedation with no or minimal discomfort, and almost all patients could be discharged without recovery – an apparent benefit to them because they did not need to take extra time from work or arrange for an escort.
Although there is a clear role for procedures performed under sedation, this and prior studies of unsedated endoscopy challenge our current sedation practice, especially the increased use of propofol for routine colonoscopy. The greater risk and cost that come with sedation may not always be justified in routine colonoscopies. The study by Garborg et al., utilizing new techniques such as water-assisted colonoscopy and CO2 colonoscopy, encourages us to reconsider our trajectory and renew our efforts toward a “less is better and safer” sedation practice.
The contents of this work do not represent the views of the Department of Veterans Affairs or the U.S. Government.
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