Management of small bowel diseases has evolved since the advent of capsule endoscopy (CE) and balloon‐assisted enteroscopy (BAE). One of the most common indications for enteroscopy is obscure gastrointestinal bleeding (OGIB), followed by small bowel stenosis, tumors, and inflammatory bowel disease. Although enteroscopes have been regarded as useful tools, correct guidelines are required to ensure that we manipulate these enteroscopes safely and efficiently in clinical practice. Herein, the Japanese Gastroenterological Endoscopy Society has developed ‘Clinical Practice Guidelines for Enteroscopy’ in collaboration with the Japanese Society of Gastroenterology, the Japanese Gastroenterological Association, and the Japanese Association for Capsule Endoscopy. These guidelines are based on the evidence available until now, but small bowel endoscopy is a relatively new technology, so the guidelines include recommendations based on a consensus reached among experts when the evidence has not been considered sufficient. These guidelines were not designed to be disease‐based, but focus on how we should use small bowel CE and BAE in everyday clinical practice.

During endoscopy, especially in patients with gastrointestinal bleeding, it is often difficult to secure the visual field. Although water immersion techniques are sometimes used to mitigate this situation [1] [2] [3], maintenance of the visual field is often difficult because the infused/injected water rapidly mixes with any luminal blood and/or residue. Poor preparation before colonoscopy also makes it difficult to secure the visual field when using water immersion or water exchange techniques. The use of gas insufflation to displace luminal contents can cause significant discomfort and difficult endoscope insertion. It is also often impossible to adequately aspirate blood, clots and residue. Although positional changes may improve visualization through gravity, this strategy is also ineffective at times. To solve these problems, we developed an innovative technique called “gel immersion endoscopy” [4]. Clear gel with an appropriate viscosity (which prevents rapid luminal mixing) is injected/infused through the accessory channel, instead of water. The viscous gel displaces luminal blood, clots and residue ([Fig. 1]). In the space occupied by the gel, we can then easily secure the visual field and perform endotherapy calmly and effectively, even in patients with massive arterial bleeding and/or poor preparation ([Video 1]). Video 1 Two patients with gastrointestinal bleeding treated by using gel immersion endoscopy. We use a jelly-like drink “OS-1 jelly” (Otsuka Pharmaceutical Factory, Tokushima, Japan) for this technique. This is a dedicated rehydration-supplement for patients with dehydration which consists of a gelling agent (polysaccharide-thickener), electrolytes, carbohydrates, and water. Since it is a food-supplement, it is considered safe for use within the digestive tract. This technique was reported with small number of procedures [4] [5] [6] [7]. However, the effectiveness and safety of this technique has not yet been studied in a large number of procedures. The aim of this study is to clarify the effectiveness and safety of the gel immersion endoscopy technique for the management of gastrointestinal bleeding and/or endoscopy after poor preparation. Received: 12 October 2020 Accepted: 15 February 2021 Publication Date: 21 June 2021 (online) © 2021. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Backgrounds and study aims Gel immersion endoscopy is a novel technique to secure the visual field during endoscopy. The aim of this study was to develop a dedicated gel for this technique. Methods To identify appropriate viscoelasticity and electrical conductivity, various gels were examined. Based on these results, the dedicated gel “OPF-203” was developed. Efficacy and safety of OPF-203 were evaluated in a porcine model. Results In vitro experiments showed that a viscosity of 230 to 1900 mPa·s, loss tangent (tanδ) ≤ 0.6, and hardness of 240 to 540 N/cm² were suitable. Ex vivo experiments showed electrical conductivity ≤ 220 μS/cm is appropriate. In vivo experiments using gastrointestinal bleeding showed that OPF-203 provided clear visualization compared to water. After electrocoagulation of gastric mucosa in OPF-203, severe coagulative necrosis was not observed in the muscularis but limited to the mucosa. Conclusions OPF-203 is useful for gel immersion endoscopy. Received: 08 January 2021 Accepted: 01 February 2021 Publication Date: 27 May 2021 (online) © 2021. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany