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Use of water jet instruments in gastrointestinal endoscopy.

In recent years, water jet instruments have been used in the field of gastrointestinal endoscopy, mainly in two clinical situations: Investigation and treatment under endoscopic view. Injecting water jet into the gastrointestinal lumen is helpful for maintaining a clear endoscopic view, washing away blood or mucous in the lumen or on the surface of the tip of the endoscope. This contributes to reducing time and discomfort of examination. Water jet technology is an alternative method for dissecting soft tissue; this method does not harm the small vessels or cause mechanical or thermal damage. However, its use in clinical settings has been limited to the transmucosal injection of water into the submucosal layer that elevates the mucosa to prepare for endoscopic mucosal resection or endoscopic submucosal dissection, instead of tissue dissection, which may occur because of the continuous water jet. A preclinical study has been conducted using a pulsed water jet system as an alternative method for submucosal dissection by reducing intraoperative water consumption and maintenance of dissection capability. This review introduces recent studies pertaining to using a water jet in gastrointestinal endoscopy and discusses future prospects.


Abstract
In recent years, water jet instruments have been used in the field of gastrointestinal endoscopy, mainly in two clinical situations: Investigation and treatment under endoscopic view. Injecting water jet into the gastrointestinal lumen is helpful for maintaining a clear endoscopic view, washing away blood or mucous in the lumen or on the surface of the tip of the endoscope. This contributes to reducing time and discomfort of examination. Water jet technology is an alternative method for dissecting soft tissue; this method does not harm the small vessels or cause mechanical or thermal damage. However, its use in clinical settings has been limited to the transmucosal injection of water into the submucosal layer that elevates the mucosa to prepare for endoscopic mucosal resection or endoscopic submucosal dissection, instead of tissue dissection, which may occur because of the continuous water jet. A preclinical study has been conducted using a pulsed water jet system as an alternative method for submucosal dissection by reducing intraoperative water consumption and maintenance of dissection capability. This review introduces recent studies pertaining to using a water jet in gastrointestinal endoscopy and discusses future prospects.

INTRODUCTION
Incidences of colorectal cancer are increasing in the developed world; in comparison with other types of examinations such as the stool occult blood test, barium enema, and computed tomography colonography, colonoscopy enables enhanced diagnostic specificity and sensitivity [1] . The incidence of gastric cancer remains high in Asian countries, including Japan. The demand for upper gastrointestinal endoscopy has been increasing annually, especially in Asian countries [2] . It requires highly advanced techniques and a learning curve exists for digestive endoscopy [1,2] . When the endoscope first appeared, it was a struggle to maintain a clear endoscopic view. The introduction of the forceps hole into the endoscope has been useful for injecting water vigorously into the gastrointestinal lumen to keep the endoscopic view clear. Endoscopes with incorporated water jet systems have been developed and released for clinical practice and are in widespread use. Water jets have also been recently used for endoscopic treatment, i.e., in endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD). This review provides an overview of recent clinical and preclinical studies of water jet instrument in gastrointestinal endoscopy.

ENDOSCOPIC VIEW
Water jet instruments were initially used to facilitate endoscopic observation. During gastrointestinal endo scopy, blood, food residue, and bubbles can impede the endoscopic view. Specifically in colonoscopy, colonic cleaning with polyethylene glycol method (PEG) helps with finding small lesions [3] . However, PEG can result in a lot of bubbles forming, hindering observation as much as the feces [4] . It is necessary to wash these out to discover the minute lesions or to treat under a clear endoscopic view. During gastroendoscopy, preme dication with mucolytic agents, such as pronase, Nacetylcysteine, or dimethylpolysiloxane before upper gastrointestinal endoscopy improves the mucosal visibility of the stomach [5,6] . It is still necessary to wash away the bubbles caused by saliva or mucus ( Figure  1). Recently, upper gastrointestinal endoscopy using nasal endoscope has rapidly become popular, as it is less painful and causes minimum vomiting reflux [710] . However, problems to be solved with this technique include lower camera resolution, insufficient light intensity, and the longer duration of the procedure as compared with that of an oral endoscopy. Attempts to use fluids such as oolong tea to clean the lens surface have been reported [11] . Manual water jet pumping prolongs inspection time [12] ; Takahashi et al [13] reported that the introduction of a water jet operated by a foot switch in the nasal gastrointestinal endoscopy reduced the average inspection time from 561 ± 123 s to 503 ± 98 s (P = 0.0002). Using a water jet to maintain a clear endoscopic view is useful for reducing time and the discomfort of examination. A water jet from an automatic lavage pump is useful to keep endoscopic view clear [14] . This is currently supplied in products from several com panies. Some models of upper gastrointestinal and colonic endoscope have separate water supply and forceps holes, which make it possible to inject water during endoscopic treatment such as hemostasis, EMR, or ESD ( Figure 2). Hemostatic procedure is one of the important techniques during endoscopic treatment like EMR or ESD. So water jet systems are widely used to find the bleeding point and to make a view during hemostasis.

INSTRUMENTS
Water jet technology was used in liver [15] and cardio vascular [16] surgeries, as well as in neurosurgery in the late 1980s [17] . When used in liver surgery, this system reduces blood loss and parenchymal trauma better than both ultrasonic aspiration and blunt dissection [18,19] . Using the water jet instrument as a surgical device provides energy using the kinetic energy of the water flowing from a nozzle at the tip of the delivery device. This energy is transmitted to the tissue surface where it ejects particles of tissue, making an incision through the organ or tissue. Mass reduction can also be achieved using water jets [15,20] . Water jet has several features pertaining to dissection that are superior to conventional instruments, including selective tissue removal with vessel pre servation based on the different tensile strengths of the tissues. Water jet devices using a continuous water flow [20] allow organ dissection while preserving vessels that are > 100200 mm in diameter [21,22] . Ano ther notable advantage is that it helps avoid thermal damage to the surrounding parenchyma, which would otherwise be inevitable using an electric scalpel, electromagnetic, ultrasonic, and laser instruments [23,24] . However, limitations have been reported to arise from the formation of air bubbles, which obscure the operative field, and the splashing of blood fluid, which could subject surgeons and nurses to cross infection [16] . These limitations may be resolved when using the instrument in a luminal organ such as the gastrointestinal tract or in laparoscopic or thoracoscopic surgery. In addition, the development of a treatment instrument with lower water consumption would help address the limitations. Endoscopic treatment such as ESD in a narrow surgical field requires the application of highly advanced techni ques by the operator. A lack of instruments that can aid this procedure preventing the risk of potential complications (thermal injury and vascular damage) is a drawback of the current ESD technique using an electric scalpel [25] . Water jet technology, which is based on a conventional, pressuredriven continuous jet [15,26] or a laser/electricallyinduced pulsed pressure jet [2729] , could provide an alternative method or novel procedure for the dissection of soft tissue without impairing small diameter vessels or causing mechanical or thermal damage during endoscopic therapy.

RESECTION
Endoscopic resection has become the standard of care for the treatment of early stage gastrointestinal tumors. EMR is performed on relatively small lesions. ESD enables the resection of large lesions in a single piece, and has low local recurrence rates [30,31] ; how ever, operation time and the risk of complications are increased [31,32] . Various knives such as the dual knife (Olympus Medical Systems Co., Tokyo, Japan), Bknife (Zeon Medical, Tokyo, Japan), ITknife, or Hook knife (Olympus Medical Systems Co., Tokyo, Japan) are used in ESD [33,34] ; these are devised for safety and ease of use. As a preparation for safe EMR or ESD, it is useful either to inject fluids such as saline or hyaluronate or inject carbon dioxide into the submucosal layer to lift the lesion from the muscular layer [35,36] . Various water jet dissectors have been developed, such as the Flush knife (Fujifilm Medical, Tokyo, Japan), Splash needle (Pentax Co., Tokyo, Japan), HybridKnife (ERBE, Tübingen, Germany), and the ENKI2 waterjet system (NESTIS, Lyon, France) [3740] ; these use continuous water flow to incise mucosa and inject fluid into the submucosal layer to lift the lesion. In contrast, the applying conventional pressuredriven continuous water jets endoscopically is limited to transmucosal injection of water into the submucosal layer for mucosal elevation prepare for EMR instead of tissue dissection [40,41] .
This may be because of the continuous water jet. An advantage of these water jet devices is that washing of the surgical field or additional submucosal injection can be performed by flushing water through the knife without changing the instrument; this results in marked improvements pertaining to the efficiency and safety of the procedure [42] . Incision capability of these devices would be mostly due to the cooperation of water jet and electric cautery. Although Lesser et al [43] attempted to use a water jet dissector to cut polyp stalks clinically in the airway; the attempt to cut or dissect a submucosal layer under gastrointestinal endoscopy has been performed only in preclinical animal experiments. A continuous water jet flow of 30 kgf/cm 2 (Angiomat 3000, LiebelFlarsheim, United States) was necessary to cut mucosa and mucosal muscle; however, injection fluid was spread in the submucosal layer in the swine stomach [44] . Kaehler et al [41] reported that a continuous water jet dissector, the Helix HydroJet (ERBE), is capable of penetrating the mucosa and creating highly selective fluid accumulation in the submucosal layer, using a water pressure of 5070 bar and an application angle of 20°90°[ 41] . Lepilliez et al [45] reported a porcine gastric ESD where continuous jet dissection using a WJ medical system (Eschmann Equipment, West Sussex, England) in vivo was technically difficult due to the lack of visual control. Using continuous water jet also poses a potential risk of obscuring the narrow endoscopic operative view due to the large amounts of water. To date, there has been no report of continuous water flow being used to dissect the submucosal layer effectively. It has been reported that a pulsed water jet was feasible at 120 mL/min of water supply, but pulsed dissection was slower than IT knife dissection in the porcine stomach [45] . That volume of water would interfere with the endoscope view in a narrow lumen such as the esophagus or large intestine. On the other hand, Sato et al [46] reported that laserinduced pulsed water jet dissection in the  A new system for cutting brain tissue preserving vessels: water jet porcine esophagus was performed safely and effectively, and the dissection rate was not different from hook knife dissection. Preservation of the vessels by water jet, which could be treated with pinpoint ablation by hemostatic equipment would contribute to reliable hemostasis ( Figure 3). They reported the feasibility of ESD of the esophagus with very small amounts of water (1.6 mL/min) and preserved microvessels. The optimal conditions for submucosal dissection are still unclear for both continuous and pulsed water jets, including the best size or shape of the nozzle, water pressure of the jet, pulse rate or volume of water supply. Since the required condition of the jet also depends on the physical properties of the tissue to be dissected [47] , the conditions may vary between the esophagus, stomach, and large intestine. Further study is needed to elucidate the optimal conditions for dissection by water jet.

CONCLUSION
In gastrointestinal endoscopy, using a water jet to maintain a clear endoscopic view is useful for reducing time and the discomfort of examination; furthermore, water jets contribute to endoscopic therapy such as ESD or EMR. Using the water jet as an operative instrument is a recent development. A continuous water jet is used to lift up the mucous layer to pretreat EMR or ESD. Hybrid products combining water jet and electric scalpel have also been developed, and their results reported. It may be difficult to dissect the submucosal layer directly using continuous flow due to its nature, but use of a pulsed water jet is feasible, with a lower volume of water consumption. Although the research reported is mostly based on animal studies limited, further research is expected in the future.