What the investigatorpropose in this protocol is a technique already used in clinical practice. It prevents the risk of bleeding and make third space endoscopy easier, quicker, safer and cheaper. Indeed, we noticed that preventive underwater coagulation of the candidate vessels during the submucosal dissection with the Hybrid Knife (HK), seal the wall of the vessel, resulting in a subsequent cut under CO2 without any bleeding. Such preventive coagulation is likely to be related with the conduction of the current underwater as it focalizes all the power on the interface between the vessel and the water, allowing a soft sealing of the vessel without cutting it. Despite widely used, there is no evidence up to know on the benefit and harm of such coagulation technique.

The hypothesis is that the use of this approach in clinical practice, especially when used to coagulate a vessel, may lead to an increase in safety, feasibility and cost-effectiveness, reducing the procedural time, the rate of complications and the need for coagulation forceps in comparison with the conventional preventive coagulation technique under CO2 insufflation. Therefore, this randomized study compares the underwater coagulation technique with the conventional coagulation technique in the CO2 setting during the submucosal dissection in third space endoscopy.

POEM will be performed under general anaesthesia in the supine position. The location of the esophagogastric junction (EGJ) will be identified and, then, after submucosal injection of saline mixed with methylene blue, a 2-cm mucosal incision carried out at 5-6 o'clock position about 10 cm above the EGJ. After, a dissection of the underlying submucosa will be performed to access the submucosal space. Then, the dissection of the submucosal layer will be continued to create the submucosal tunnel down to the narrower submucosal space at the EGJ and 2-3 cm into the cardia. During the submucosal tunnelling, coagulation of vessels will be performed with HK using SWIFT COAG E3, 89 W in the underwater setting in the treatment arm or with the standard technique in the CO2-setting in the conventional group. After, the myotomy of the circular muscular layer will be performed from 2-3 cm below the mucosal incision until 2-3 cm below the EGJ in both groups. In some cases, a full thickness myotomy, including the longitudinal muscular layer, will be carried out. Finally, complete closure of the mucosal entry site will be achieved with haemostatic clips. The procedure time, the number of instrument exchanges and bleeding episodes requiring the use of coagulation forceps during the procedure will be documented from start of submucosal tunnelling until final clip closure in both groups.

Fujifilm high-definition gastroscopes (Fujifilm Co., Tokyo, Japan) with a 2.8-mm operative channel and a transparent distal cap attachment will be used in both groups. A submucosal lift with saline mixed with methylene blue through a 23 G injection needle will be accomplished for the mucosal entry. POEM will be carried out using a HK (Erbe Elektromedizin GmbH, Tübingen) in both groups. This instrument has an outer diameter of 2.1 mm and an inner diameter of 1.2 mm with both electrosurgical and water-jet (WJ) surgery technologies in one device. The HK combines needle-less submucosal injection, cutting, dissection and coagulation in one instrument. The modular VIO generator (VIO 3, Erbe Elektromedizin GmbH, Tübingen, Germany) will be used as an electrosurgical system in combination with the ERBEJet 2 WJ surgery system in both groups. A slightly methylene blue-stained isotonic saline solution will be used for submucosal injection with the WJ technique in both groups. Mucosal incision and myotomy will be carried out using ENDO CUT Q 2-3-3 and ENDO CUT Q 2-3-3, respectively, in both groups.

Inclusion criteria:

All >18 years-old patients undergoing ESD for superificial GI neoplastic lesions or POEM for esophageal achalasia

Exclusion criteria:

patients on antithrombotic/anticoagulant therapy patients suffering from bleeding disorders patients with esophageal and/or gastric varices patients previously treated for the same reason patients who were not able or refused to give informed written consent. vessels smaller than the knife inner diameter (1.2 mm)