Cold polypectomy has the advantages of simple operation, less time-consuming and fewer complications. Guidelines have recommended cold snare polypectomy (CSP) to resect small polyps sized <9 mm. CSP was designed to improve the complete resection rate and reduce adverse events. Investigators hypothesize that CSP is better than conventional hot snare endoscopic mucosal resection (HS-EMR) in the presence of injured submucosal arteries detected in the submucosal layer for 10-19 mm nonpedunculated colorectal polyps, resulting in lower delayed bleeding after CSP of 10-19 mm nonpedunculated colorectal polyps.

Cold polypectomy has the advantages of simple operation, less time-consuming and fewer complications. Guidelines have recommended cold snare polypectomy (CSP) to resect small polyps sized <9 mm. CSP was designed to improve the complete resection rate and reduce adverse events. Investigators hypothesize that CSP is better than conventional hot snare endoscopic mucosal resection (HS-EMR) in the presence of injured submucosal arteries detected in the submucosal layer for 10-19 mm nonpedunculated colorectal polyps, resulting in lower delayed bleeding after CS-EMR of 10-19 mm nonpedunculated colorectal polyps. The primary outcome measure was the presence of injured submucosal arteries detected in the submucosal layer. The secondary outcomes included immediate bleeding and the frequency of delayed bleeding requiring endoscopic treatment within 2 weeks after polypectomy. Immediate bleeding was defined as spurting or oozing which continued for more than 30 seconds.

Inclusion Criteria:

• at least one polyp sized 10-19 mm (Paris classification Is or IIa) revealed by endoscopic examination.

Exclusion Criteria:

1. American Society of Anesthesiologists status class 3 or above
2. poor bowel preparation (Boston Bowel Preparation Scale <6 points)
3. endoscopic features indicating submucous infiltration or malignancy
4. oral anticoagulants,or antiplatelet agents, or known blood coagulation disorders, or bleeding tendency
5. a history of colorectal resection
6. emergent colonoscopy (haemodynamic instability and/or continued active gastrointestinal bleeding and/or requiring intensive care patients)
7. inflammatory bowel disease, familial polyposis and colorectal cancer
8. pregnancy or lactation
9. severe cardiopulmonary dysfunction, cirrhosis, chronic kidney disease, other malignant tumours or severe infectious diseases.