This is a single centre randomised controlled study comparing underwater clip closure versus conventional gas insufflation clip closure of post-resection defect in patients undergoing colonic endoscopic resection. The investigators hypothesize that underwater clip closure would be faster than conventional closure under gas insufflation.

Endoscopic submucosal dissection (ESD) is a minimally invasive technique that has been increasingly applied to superficial colorectal tumours over the past two decades (1, 2). Although serious complications with this procedure are uncommon, both significant delayed haemorrhage (1-2%) and perforation (4-6%) are recognised complications (3). Although perforation is generally recognised and treated at time of endoscopy, delayed bleeding often requires repeat readmission and endoscopy for haemorrhage control. There is growing evidence to support prophylactic clip closure of mucosal defects to reduce incidences of delayed haemorrhage.

Prophylactic clip closure of mucosal defects (≥20mm) after colonic ESD is supported by large retrospective case series. In a series of 524 lesions in 463 patients, Liaquat et al. (2013) reported prophylactic clipping of resection sites to close mucosal defects versus non-closure, reduced delayed haemorrhage (9.7% vs 1.8%) (4). Ogiyama et al. (2018) reported similar findings in a series of 156 lesions (0% vs 8.2%, p=0.008) (5).

Prophylactic defect closure also has a theoretical benefit in reducing delayed perforation from unrecognised muscular breach during dissection. Though it is recognised that there is a paucity of evidence to support mucosal apposition in reducing delayed perforation rates (~0.2%) (3). This is likely due to the underpowered published studies and a very low event rate.

For these reasons, it has been routine practice of many endoscopists for clip closure of mucosal defects after endoscopic resection of large colorectal neoplasia. However, this technique remains technically challenging within the narrow colonic space and at times may not be feasible. The 'underwater closure technique' in mucosal defect closure of colonic and duodenal endoscopic resections has promising early results. Compared to conventional CO2 insufflation clip placement, at the time of mucosal closure this technique applies luminal water infusion to 'float' the resection borders and downsize the target. Early experience suggests this technique facilitates easier apposition of resection borders and complete closure. There are currently no randomized trials comparing these clip closure techniques.

The aim of the study is to evaluate whether prophylactic underwater closure technique facilitates easier ESD mucosal defect closure compared to conventional clip closure.

This is a single centre prospective randomized controlled trial. Consecutive patients undergoing endoscopic resection for colonic lesions would be recruited. Participants would be randomized to receive prophylactic conventional clip closure versus underwater technique.

Inclusion Criteria:

• Patients undergoing elective endoscopic resection
• Colorectal superficial neoplasm with a resultant mucosal defect of ≥20mm
• Age >18 years old

Exclusion Criteria:

• Patients on anticoagulation (Warfarin or other direct oral anticoagulants)
• Muscular perforation during the endoscopic resection
• Incomplete endoscopic resection
• Lesions arising from surgical anastomotic site
• Marked electrolyte abnormalities
• Other cases deemed by the examining physician as unsuitable for safe treatment
• Patients who refused to participate