To investigated the hemostatic ability of the S and F1-10 methods in clinical and ex vivo studies.

The hemostatic abilities of the two methods were analyzed retrospectively in all six gastric endoscopic submucosal dissection cases. The treated vessel diameter, compressed vessel frequency, and bleeding frequency after cutting the vessels were noted by the recorded videos. The coagulation mechanism of the two power settings was evaluated using the data recording program and histological examination on macro- and microscopic levels in the ex vivo experiments using porcine tissues.

F1-10 method showed a significantly better hemostatic ability for vessels ≥ 2 mm in diameter and a trend of overall better coagulation effect, evaluated by the bleeding rate after cutting the vessels. F1-10 method could sustain electrical current longer and effectively coagulate the tissue wider and deeper than the S method in the porcine model.

F1-10 method is suggested to achieve a stronger hemostatic effect than the S method in clinical procedures and ex vivo models.

Electrosurgery is used in many fields of medicine and is one of the most commonly used energy system in surgery. Basic understanding of electricity is required for the safe use of electrosurgical technology for patient care[1-6]. In the endoscopic field of gastroenterology, endoscopic mucosal resection and endoscopic submucosal dissection (ESD) are popular therapeutic strategies to resect benign and early cancerous lesions that require the use of an electrosurgical generator[7]. Preventing bleeding during operation, especially in ESD, is one of the most important factors to accomplish safe and successful tumor removal[8].

The modern electrosurgery has various coagulation modes. The forced coagulation utilizes a high output voltage > 200 Vp with an interrupted waveform. The forced coagulation creates sparks, which coagulate on superficial tissues. At the same time, a high output voltage coagulation mode, such as the forced coagulation, generally has a cutting ability[9]. In ESD, it can create appropriate coagulation for small vessels, such as the capillaries; however, its effect for non-small vessels larger than the capillaries is insufficient, because the non-small vessels are cut before being dehydrated adequately and have a risk of bleeding. Therefore, the forced coagulation mode is thought to be unsuitable for precoagulation of large vessels.

On the other hand, the peak voltage between the active electrode and the target tissue in the soft coagulation mode is limited to < 200 Vp. This mode does not cause any sparks, only uses Joule’s heat, and avoids rupturing the vessels[10,11].

We previously reported the effectiveness of vessel-sealing with endoknife compression using the soft coagulation mode (S method) in ESD[12]. This method is useful for coagulation without bleeding before cutting relatively large vessels, such as those penetrating between the muscularis propria. However, an important limitation of this mode is that the current cannot flow to the tissue when its resistance becomes too high because of the limited voltage below 200 Vp. Therefore, it has a risk of inadequate coagulation when the vessels are too large and the tissue resistance becomes too high while processing. Owing to this, hemostatic forceps were generally used to precoagulate large vessels. Therefore, we required a more effective setting for large vessels. The forced coagulation mode is usually not used for precoagulation; however, we found when the HF (high-frequency) power is reduced to a quite low level, it can avoid generating sparks. It was suggested that the forced coagulation mode with a low HF power setting be used for precoagulation to process larger vessels. Based on these, vessel-sealing with endoknife compression using the forced coagulation mode with low HF power setting (Effect 1, 10 W: F1-10 method) was also used in our facility (The peak voltage in the forced coagulation is adjusted from Effect 1 to 4; Effect 1 is the lowest peak voltage setting).

Accordingly, this setting hardly causes vessel rupture in spite of using the forced coagulation mode. Therefore, we retrospectively analyzed the effectiveness of bleeding control by the S and F1-10 methods to find the optimum power setting. Moreover, the mechanism of coagulation was analyzed by ex vivo experiments using porcine tissues to further evaluate the coagulation ability of these two settings.

ESD has enabled an endoscopic en bloc resection of large tumors in the esophagus, stomach, and colorectum. However, intraoperative bleeding remains one of the major complications during ESD, although bleeding improved to some degree by the development of devices, such as endoknives, hemostatic forceps, and electrical surgical units[14]. In actual practice, it sometimes takes a lot of time to stop bleeding in ESD; once the lesion is bleeding, it is difficult to recognize the submucosal layers as these are blood-stained, making the procedure more difficult to perform[15]. The prevention of intraoperative bleeding is important to achieve a safe ESD. The FlushKnife-BT, which has a ball tip on top of the needle, improved the hemostasis effect compared with the conventional needle-type FlushKnife because its round ball tip compressed the vessels widely and decreased the current density[13]. However, the FlushKnife-BT still pose a bleeding risk as the vessels are cut before adequate coagulation.

It was suggested that the S method is useful for precoagulation. Soft coagulation regulates the peak voltage below 200 Vp, and it can dehydrate the vessels without any spark or rupture. Therefore, this mode was thought to be appropriate for this technique. However, its efficacy was insufficient, especially for large vessels in the upper and middle thirds of the stomach[16]. We introduced this technique using the F1-10 setting as aforementioned by modifying the peak voltage and power setting, and the usefulness of the S and F1-10 methods were compared in this study.

In the clinical study, the bleeding rates after vessel processing for large vessels were 26.9% and 3.4% in the S and F1-10 methods, respectively, which were significantly different. The median current elapsed time was longer, and the width and depth of coagulation were wider and deeper in the F1-10 method than in the S method in the ex vivo study.

Forced coagulation mode usually generates the sparks and fulguration accompanying the cutting function added to the coagulation. It was known that this mode was unsuitable for the endoknife precoagulation. However, when the peak voltage and electrical power in the forced coagulation were decreased to the level of the F1-10 setting, the current elapsed time became much longer than that of the S method and sparks were not observed in both ESD and experiment with the porcine tissue.

While the electrode heat dehydrates the tissues and increases tissue resistance, the electric current gradually decreased and turned off. This mechanism can be explained by Ohm's law, in which voltage (U) = resistance (R) × electric current (I). Forced coagulation creates a higher voltage than that of soft coagulation and could keep the current flow much longer even after the tissue resistance increased, as shown in the experiment. It can imply that under the generation of Joule's heat without sparks, the coagulation range is decided by the current elapsed time. For this mechanism, the F1-10 method achieved a wider and deeper coagulation area than the S method.

Our study showed the usefulness of the F1-10 method from the point of superior coagulation ability during ESD. On the other hand, this method may have the risk of perforation due to deep coagulation. However, we did not experience intraoperative perforation using the F1-10 method even during ESD in the esophagus and colorectum, which have thinner walls than the stomach. Further, no obvious increase in the postoperative perforation rate has been observed since the induction of the F1-10 method in our facility until the present. Such finding may be explained by the vessel-sealing with endoknife compression technique, which applies electrical energy after compressing and pulling the vessel apart from the muscle layer. Its concept is essentially the same as that of coagulation using hemostatic forceps. However, it must be emphasized that too much coagulation on the muscularis propria should be avoided to prevent deep coagulation. This caution is similar as with the hemostatic forceps should be used[17].

Recently, one research reported that the bleeding rate after endoknife precoagulation was not significantly different between the use of the F1-10 method and the hemostatic forceps with the soft coagulation during gastric ESD; further, the use of F1-10 did not result in serious intraoperative bleeding and reduced the frequency of using hemostatic forceps[18]. The F1-10 method was demonstrated to be as safe and effective for bleeding prevention as hemostatic forceps.

However, there were some limitations in our study. First, the vessels processed by hemostatic forceps were excluded from the analysis (12 in the S method and one in the F1-10 method); it has a potential to be a selection bias, however, those included were only the vessels larger than the ones for which precoagulation was not accomplished. Therefore, even if endoknife precoagulation was attempted, it was highly expected that it would fail. Although there is no research that compares the precoagulation effectiveness between the S-method and hemostatic forceps method yet, it is empirically known that the coagulation ability of hemostatic forceps is stronger than the S method; further, precoagulation using hemostatic forceps can reduce the bleeding risk[19,20]. If there was a selection bias, it would be for the advantage of the S method in this study. However, the result still suggested that the F1-10 method was superior to the S method. Second, the clinical data shown are achieved under the use of the FlushKnife-BT, which has a ball tip and is capable of firm vessel compression. This FlushKnife-BT method should not be simply applied when precoagulation with different types of ESD knives is performed. The ideal generator setting should be investigated for each bleeding control strategy and for different types of devices. Further, only a skilled endoscopist performed the ESD in the present study. The generalizability of the result in this study remains uncertain; however, we believe that if proper precoagulation procedure is conducted, similar results could be obtained.

In conclusion, the vessel-sealing with endoknife compression technique using the F1-10 method is better than that using the S method, especially for large vessels. Thus, the F1-10 method is considered to promote a safer and better quality ESD.

We would like to thank Masaki Yamazaki from AMCO Incorporated (Tokyo, Japan) for the review of terminology matters, and AMCO Incorporated (Tokyo, Japan) for supporting the VIO DOKU.