Deep dive into water-aided colonoscopy – underwater techniques without a splash

The infusion of water to aid colonoscopy dates back over several decades, with the evolution of the practice having covered many techniques. Investigators and practitioners have employed a combination of gas (air or CO₂) and water without suction of the infused water during insertion (water immersion), or infusion of water with removal of water and debris, as well as residual gas, during insertion (water exchange), and underwater resection to remove lesions [1]. Underwater resection entails the immersion of polyps in water to assist polypectomy, underwater endoscopic mucosal resection (UEMR), and underwater endoscopic submucosal dissection (UESD). The technique without gas instillation reduces colonic distension and elongation, minimizing loop formation, decreasing pain, and enhancing the success of insertion in unsedated patients. Water exchange with the removal of infused water along with colonic debris during insertion improves the quality of bowel preparation during withdrawal in both unsedated and sedated patients, and minimizes cleaning-associated distractions in the search for polyps. Quality improvement with water exchange has shown increases in the adenoma detection rate, with the immersion of the polyps in water enhancing completeness and ensuring the safety of lesion removal.

“The emphasis on patient outcome advantages alone may however be insufficient to promote the application of some of the novel underwater approaches in clinical practice.”

In randomized controlled trials (RCTs) that have compared conventional versus underwater techniques, outcomes have included successful cecal intubation, the lesion detection rate, complications, the lesion miss rate, completeness of lesion removal, the lesion recurrence rate, endoscopy room turnover efficiency, and endoscopist and patient satisfaction. Efficacy has been repeatedly demonstrated, but at a cost of prolonged procedure times [1].

In one systematic review and meta-analysis, UEMR was shown to be an effective technique for removing colorectal lesions. UEMR resulted in a higher en bloc resection rate (removal of a tumor in its entirety, along with a healthy margin of tissue surrounding it) and a lower recurrence rate when compared with conventional EMR (CEMR). Both techniques had comparable resection times and safety profiles [2]. Another meta-analysis confirmed that UEMR improved the en bloc resection rate, without increasing the procedure time or the rates of recurrence or adverse events [3]. A third systematic review and meta-analysis showed UEMR could be a safe and efficient substitute for CEMR when removing ≥10-mm sessile or flat colorectal polyps. The authors suggested that more studies verifying the advantages of UEMR over CEMR were needed to promote its application [4].

In a Korean RCT, UESD was shown to be superior to CESD in terms of total procedure time and dissection speed. UESD was recommended as the preferred method for the resection of large laterally spreading tumors [5]. An in-press meta-analysis is reporting that UESD was faster in patients with colorectal lesions and had comparable rates of en bloc and R0 resection (microscopically clear resection margin, with no tumor remaining in the primary tumor bed) and adverse events when compared with CESD [6]. The key advantage of the underwater approach was the rapid dissipation of thermal energy during the application of electrocautery for removal of polyps. The “heat-sink” effect demonstrated in a porcine colon model was previously postulated to be a factor in decreasing thermal injury to the deeper layers of the colon wall [7].

Against the backdrop of these recently reported underwater resection methods, the current issue of Endoscopy features a Japanese prospective RCT comparing CESD and UESD for superficial colorectal neoplasms (SCNs) [8]. In this single-center study, patients with SCNs meeting the indications of the Japanese guidelines for ESD were randomly assigned to undergo either CESD or UESD, performed by a single expert. The primary end point was dissection speed, defined as the specimen area per ESD time. The data of 69 CESD and 70 UESD cases were compared. No significant differences were found in the median dissection speeds (17.4 and 19.9 mm²/min, respectively; P = 0.19). Multiple regression analysis revealed that a suitable positional relationship between the lesion and gravity (nongravity side for CESD and gravity side for UESD) was independently and positively associated with dissection speed (P < 0.001). En bloc resection was achieved without perforation in all cases. The incidence of post-ESD coagulation syndrome was not significantly different between the two groups (4.3% vs. 2.9%, respectively; P = 0.68). The authors concluded that UESD did not expedite dissection speed in the study patients. The choice of dissection speed as the primary outcome reflected the considerable interest in demonstrating a faster underwater method.

The plethora of outcome measures have repeatedly confirmed the efficacy of underwater resection. More studies verifying the advantages of UEMR over CEMR have been recommended [4] and they will certainly provide added incentives to promote the underwater resection approach. The emphasis on patient outcome advantages alone may however be insufficient to promote the application of some of the novel underwater approaches in clinical practice. For the endoscopist with experience in the conventional method, learning any new underwater technique will require the unlearning of part of the mastered conventional method. The extra time needed to learn and practice the novel maneuvers may present a financial disincentive, as reimbursement is tied to caseloads rather than outcomes. The process can be an impediment to the adoption of selected new methods.

A shift in the training paradigm may provide a plausible solution. For novice education, traditional training would begin with the conventional technique first, followed by the underwater technique. An alternative to the traditional paradigm is to consider conducting the training “simultaneously”. This strategy avoids the need for the “trainee” to unlearn part of the ingrained conventional method when the underwater method is taught. One recent report suggested that learning the underwater technique of water exchange appeared to be easier, with a better outcome in terms of a significantly higher polyp detection rate, and was welcomed by novice trainees when training in the underwater and conventional techniques were caried out side-by-side in alternate cases [9]. Whether adoption of the new training paradigm can hasten the translation of underwater skills into practice, enabling better patient outcomes to be realized among the next generation of practitioners, deserves to be studied.

Publikationsverlauf

Artikel online veröffentlicht:
08. Januar 2025

• References

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