A new bipolar device for sealing and cutting: ex and in vivo studies for performance evaluation

Abstract

Introduction

A novel multipurpose bipolar radiofrequency instrument, the Erbe Dissector (EDS), which simultaneously seals and cuts tissue, was developed. Ex vivo sealing rate and time, burst pressure, jaw temperature and thermal spread were studied in porcine renal arteries.

Material and methods

In vivo, 13 surgical tasks were performed in two pigs: beside sealing rate and time, overall performance in sharp and blunt dissection, tissue sticking, hemostasis, precision, etc., were evaluated by four surgeons compared with ENSEAL G2 (EG2) using surveys on a Likert scale (1 = very poor; 5 = very good).

Results

Ex vivo, the EDS sealing rate was 91.7% (33/36 arteries) at an average sealing time of 2.1 s (range 1.7–2.8) and a burst pressure of 1040 ± 350 mmHg. The maximum jaw temperature was 87 ± 4 °C and the mean lateral thermal spread was 0.8 ± 0.2 mm. In vivo, the sealing rate for arteries and veins was 92.6% (50/54) and the median seal and cut time was 1.6 s (range: 1.3–2.9). The average EDS performance score across all tasks was 4.4 ± 0.6 Likert points. For five shared tasks, EDS was better than EG2 (4.4 ± 0.5 versus 3.4 ± 0.6 Likert points; p = 0.016).

Conclusions

EDS seals and cuts arteries and veins rapidly with good safety and user-friendliness.

Keywords:

• Vessel sealing
• electric cutting
• animal model
• seal and cut time
• sealing rate

Introduction

Since its invention more than 60 years ago, bipolar electrosurgery has become indispensable in every operating theatre for both minimally invasive and open surgical procedures [1]. Modern bipolar vessel sealing devices unite three steps in one instrument: tissue dissection, vessel sealing and cutting, which consequently leads to reduced operating time [2].

The tissue-recognizing technology for electrocoagulation has been proven to reliably coagulate and seal vessels up to 7 mm in diameter [3–5]. With further improvement of technique and development of new electrosurgical instruments unwanted side-effects such as heat-induced lateral thermal damage and tissue sticking to the instrument in the cutting process could be minimized [6,7]. In addition to reliability, safety and efficacy, ergonomic aspects of handling the electrosurgical instrument and its applicability in a wide range of indications and conditions are becoming increasingly important. Energy-based devices are established in many different interventional disciplines: general surgery, visceral surgery, thoracic surgery, urology and gynecology and for various surgical procedures such as thyroidectomy, colon resection, liver resection, splenectomy, lung resection, nephrectomy and hysterectomy [8–14]. Thus, the instruments must meet high demands. On the one hand, material, specific modes and electrical parameters need to be customized for the respective application; on the other hand, devices should fit a broad mass of different users with diverging conditions, preferences, needs and expectations.

The newly developed Erbe Dissector (EDS, Erbe Elektromedizin GmbH, Tuebingen, Germany) is intended for sealing and cutting vessels up to 5 mm in diameter. However, it is not limited to vessels, but can also be used to dissect other tissues such as connective tissue with small vessels. Unlike conventional laparoscopic vessel sealers, EDS can seal and cut electrically. Thereby EDS cuts and coagulates the tissue at the same time.

The aim of this study was to evaluate the performance and safety of the new EDS. In a first step, sealing rate and time, burst pressure and thermal spread were evaluated in an ex vivo setting. In a second step, the performance of EDS was tested in a prospective, randomized, controlled in vivo animal study regarding the sealing rate, sealing time and acute complications. In addition, handling and usability were evaluated with intra- and postoperative questionnaires including a side-by-side comparison of EDS and ENSEAL G2^® (EG2, Ethicon, Johnson and Johnson, Cincinnati, OH, USA). As the usability of the device was in focus, a product was defined that also simultaneously cuts and coagulates tissue using bipolar technology. EG2 coagulates tissue electrically as long as the knife is pushed forward trough the tissue.

Material and methods

Ex vivo bench testing

Renal arteries from freshly (<24 h) slaughtered pigs were clamped, sealed and cut using the EDS device and the accompanying new dedicated EDS generator mode (VIO® 3 high-frequency generator, Erbe Elektromedizin GmbH). The instrument has been developed for ease of use. The system, especially the jaw geometry, is designed for a fast and precise dissection (yellow button), which is further enhanced by a short sealing and cutting time. Coagulation is possible with the blue button. Three EDS instruments and 12 arteries per instrument were used. In a semi-automated burst pressure test setup (Erbe Elektromedizin GmbH, Tuebingen, Germany) each vessel part of the sealed artery was pressurized with tap water to the standard systolic blood pressure of 120 mmHg to measure the vessel diameter as described previously [2]. Then, the intraluminal pressure of each vessel part was increased to 380 mmHg. After a holding time of 60 s the pressure was gradually increased until the seal burst. The maximum recorded pressure immediately prior to burst was recorded as the burst pressure (BP). The sealing rate of all sealed vessel parts was defined as the percentage of successfully sealed vessels with a BP ≥ 380 mmHg after a holding time of 60 s. 360 mmHg covers three times the physiological systolic pressure of 120 mmHg. In the present test setting, to assure a pressure of 360 mmHg for 60 s, an addition of 20 mmHg was added to cover measurement uncertainty, resulting in 380 mmHg. For the maximum jaw temperature, the jaws were blackened and the jaw’s outer temperature was measured during activation with an IR camera in a top-down view. Thermal damage was determined microscopically by measuring the width of the coagulation necrosis. For this, the distance between the edge of the sealing instrument and the edge of the visible tissue discoloration was measured [14].

In vivo animal testing

Two female German Landrace pigs (Sus scrofa domesticus) were used, aged approximately four months with a body weight of 59 kg and 62 kg at intervention. From the time of purchase until the surgical procedure, the animals were kept in cages at a temperature of approximately 20 °C and a relative humidity of approximately 60% with natural day-night cycles in accordance with the EU directive 2007/526/EG and the EU guideline 2010/63/EU. They received standard diet and tap water ad libitum. After an adaptation period in the Research Animal Care Facility, the pigs were deprived of food (not water) on the evening before the surgical procedure. The pigs were medicated and anesthetized according to the following protocol: premedication was administered by intramuscular injection of atropine (0.05 mg/kg), azaperone (4.0 mg/kg; Stresnil®, Elanco GmbH, Cuxhaven, Germany), ketamine (14.0 mg/kg, Ketaminol®, Intervet GmbH, Vienna, Austria) and midazolam (1.0 mg/kg; Midazolam-hameln, hameln pharma GmbH, Hameln, Germany). Before tracheal intubation, a bolus of 2.0–5.0 mg/kg propofol (Propofol Fresenius MCT, Fresenius Kabi Deutschland GmbH, Bad Homburg, Germany) was given intravenously. During the intervention the animals were ventilated and kept in deep anesthesia with isoflurane (0.8 − 1.6 vol%, Isofluran CP®, CP-Pharma Handelsgesellschaft mbH, Burgdorf, Germany) and for analgesic coverage with fentanyl (Fentanyl-ratiopharm, ratiopharm GmbH, Ulm, Germany) at an intravenous dose of 30 − 100 µg/kg/h. At the end of the intervention, the animals were painlessly killed with a lethal dose of the euthanasia solution T61 (Intervet GmbH, Vienna, Austria).

Four experienced operators (two gynecologists, one visceral surgeon, one thoracic surgeon) performed 13 surgical subtasks and sealed a total of 63 vessels with EDS (Figure 1). The surgical subtasks were divided into laparoscopic procedures (2 × partial hysterectomy, 2 × dissection of small intestinal mesentery, partial rectal resection and lymphadenectomy) and open surgery procedures (dissection for splenectomy, lobectomy of the lung, dissection to a thoracic vessel, dissection for sealing of the internal thoracic artery, splenectomy, nephrectomy and cholecystectomy). The diameters of all sealed vessels were measured in open surgery with a caliper and laparoscopically with reference points on the instrument tip. In both cases, vessel sizes were documented before the sealing procedure. Although EDS is intended to seal vessels up to 5 mm in diameter, vessels up to 6 mm in diameter were included in the seal failure assessment as a safety buffer. Seal failure was defined as a bleeding that occurred when the instrument was opened, after the generator had given a signal of completed sealing. Seal failure and seal and cut time were recorded during the sealing procedure. The occurrence of bleeding was documented throughout the interventions. The bleeding rate represents the number of bleedings over all instrument activations, irrespective of tissue type. Bleedings could be treated directly with the blue button of the instrument. Five surgical subtasks (partial rectal resection, lymphadenectomy, dissection to a thoracic vessel and two dissections of small intestinal mesentery) were also performed with EG2 for side-by-side comparison. Immediately after each surgical subtask, operators were interviewed with regard to performance aspects using a 5-point Likert response format (Figure 4). At the end of the whole surgical procedure, a post-operative questionnaire on overall performance was completed with each operator (Table 1). If the topic was not used or not relevant during a subtask, the corresponding question was marked ‘not applicable’. Each question was answered by at least two operators and for at least eight of the 13 subtasks performed with EDS and three of the five subtasks performed with EG2 (Supplementary material 1).

Figure 1. Overview of the in vivo study design including open or laparoscopic surgical subtasks per operator. Four experienced operators, two gynecologists, one visceral surgeon and one thoracic surgeon performed 13 surgical subtasks. EDS = Erbe Dissector, EG2 = ENSEAL G2.

Table 1. Intraoperative and postoperative questionnaire (Likert items).

Topic	Statement
Tissue sticking^a	Adhesion of tissue to the instrument is not disturbing.
Sharp dissection (thermal spread)^a	Unintended thermal lateral damage during dissection does not occur.
Sharp dissection (speed of dissection)^a	Working speed during dissection is optimal.
Blunt dissection (repositioning tissue)^a	The instrument is optimal for repositioning the tissue.
Blunt dissection (spreading tissue)^a	The instrument is optimal for spreading tissue to separate tissue layers.
Blunt dissection (visibility of tissue)^a	I am able to see the contact point between instrument and tissue during blunt preparation.
Blunt dissection (feasibility of otomy creation)^a	The instrument is optimal for creating an otomy.
Quality as a surgical gripping forceps^a	The instrument is ideally suited for use as a gripper.
Hemostasis with coagulation mode^a	Hemostasis during coagulation with the blue button is optimal.
Information on tissue strength/tightness^a	I am able to feel the tissue consistency via the instrument.
Precision (working in small steps)^a	I am able to work precisely by proceeding in small steps.
Precision (close to sensitive structures)^a	I am able to work precisely in the immediate vicinity of a sensitive structure.
Feasibility for work in tight spaces^a	Working in tight spaces is optimally supported by the instrument.
Overall rating^b	How do you rate the instrument overall?
Working speed^b	How do you rate the working speed?
Precise dissection^b	How do you rate its use for fine or precise surgical steps (e.g., lymphadenectomy)?
Hemostasis^b	How do you rate use of the device for surgical steps where blood-dry sealing of thicker tissue layers is important (e.g., cutting of ligaments in hysterectomy)?
Thermal lateral damage^b	How do you evaluate the lateral thermal dispersion zone?
Ergonomics^b	How do you rate the ergonomics of the instrument?
Usability (manual forces)^b	How would you rate the manual force required to operate the instrument?
Usability (accessibility of all control elements)^b	How do you rate the accessibility of all control elements?
Surgical smoke (visibility)^b	The smoke generated by the system does not impair the view in the operating field.
Surgical smoke (smell)^b	The smoke produced by the system does not interfere with smell.
Tissue carbonization^b	There is no charring of tissue during dissection.
Overall rating^b	How do you rate the instrument overall?
Working speed^b	How do you rate the working speed?

^aintraoperative questions.

^bpostoperative questions.

All data were evaluated using GraphPad Prism version 7 for Windows (GraphPad Software, La Jolla, CA, USA, www.graphpad.com). Descriptive statistics (mean/median, standard deviation/interquartile range and proportion) were performed to describe the basic features of the collected data. Differences between independent quantitative data (seal and cut time, burst pressure, vessel diameter) were detected using a two-tailed Student’s t-test provided that the data were normally distributed. The normal distribution was confirmed with a KS test (Kolmogorov–Smirnov Test). For analysis of non-normally distributed samples, the Mann–Whitney test was used. Outcomes from the Likert items were treated as continuous and normally distributed [15]. P values <0.05 were considered statistically significant.

Results

Ex vivo bench testing

The vessel sealing success rate when using EDS for porcine renal arteries with a mean diameter of 4.4 ± 0.5 mm (range 3.2 mm − 5.4 mm) was 91.7% (33/36 arteries) (Figure 2(a)). The mean burst pressure of the corresponding vessel parts was 1040 ± 350 mmHg (range 293 mmHg − 2056 mmHg, n = 72 vessel parts). Median seal and cut time was 2.1 s (range 1.7 s − 2.8 s, n = 36 arteries) and did not correlate with the vessel diameter (R²=0.003, n = 36). Maximal jaw temperature was 87 ± 4 °C (range 78 °C − 95 °C, n = 36 arteries) and lateral thermal spread was 0.8 ± 0.2 mm (range 0.5 mm − 1.3 mm, n = 36 arteries). Figure 2(a) represents an example of a sealed and cut artery and the associated lateral thermal damage. The three EDS instruments included in this test (n = 12 arteries per instrument, n = 24 vessel parts per instrument) did not differ significantly in terms of burst pressure (p = 0.82, n = 72) or vessel diameter (p = 0.82, n = 72).

Figure 2. For the Erbe Dissector (EDS) with a dedicated EDS generator mode (a) Vessel sealing success rate ex vivo for renal arteries and microscope image of sealed vessel with the seal zone and lateral thermal spread (b) Vessel sealing success rate in vivo for vessels with diameters 2-6 mm (filled), arteries (dotted), veins (hatched) and all vessels (no filling).

In vivo animal testing

Sealing performance of the Erbe dissector

A total of 63 vessels, 30 arteries (diameter range 2.0 mm − 8.0 mm) and 33 veins (diameter range 2.0 mm − 8.8 mm) were sealed during the vessel sealing tasks. The sealing of two veins (Ø 7.0 mm, Ø 5.4 mm) and three arteries (Ø 5.8 mm, Ø 5.3 mm and Ø 4.3 mm) failed, resulting in a vessel sealing success rate of 92.1% (58/63 vessels) (Figure 2(b)). The success rate was similar (92.6%, 50/54) regarding only vessels with diameters between 2.0 mm and 6.0 mm. For this range, the diameter of arteries had a mean of 3.7 ± 1.0 mm (range 2.0 mm − 5.8 mm, n = 27) and of veins 4.2 ± 1.2 mm (range 2.0 mm − 5.9 mm, n = 27). The success rate for veins (96.3%, 26/27) was similar to that for arteries (88.9%, 24/27, p = 0.61). The bleeding rate during the surgical subtasks and vessel sealings with EDS for all 774 activations, irrespective of tissue type, was 1.2% (9/774). Of these nine bleedings, two occurred during laparoscopic partial hysterectomy, one during laparoscopic partial rectal resection and one during open splenectomy. The remaining five bleedings correspond to the above-mentioned seal failures in arteries and veins.

During vessel sealing the median seal and cut time for arteries was 1.6 s (range 1.3 s − 2.6 s, n = 24) and also for veins 1.6 s (range 1.5 s − 2.9 s, n = 25) and did not differ significantly (p = 0.86) for these vessel types (Figure 3(a)). The median seal and cut time for all vessels between 2 mm and 6 mm was 1.6 s (range 1.3 s − 2.9 s). The seal and cut time and vessel diameter did not significantly differ between arteries and veins (p = 0.8617 & p = 0.0911). Therefore, the correlation was calculated for the pooled group. The seal and cut time was not a function of the vessel diameter (R2 = 0.03, p = 0.201, n = 49) (Figure 3(b)).

Figure 3. (a) Seal and cut time (median with IQR) with the Erbe Dissector (EDS) with a dedicated EDS generator mode for vessels with diameter 2-6 mm (squares), arteries (points) and veins (triangles) (b) Linear regression (solid line) of the seal and cut time and vessel diameter for the pooled group of arteries and veins.

Side-by-side comparison of the Erbe dissector and ENSEAL G2

Handling and usability of EDS and EG2 were evaluated with intra- and postoperative questionnaires using a 5‑point Likert scale (1 = very poor; 5 = very good). Overall performance of EDS and EG2 is shown in Figure 4, where the mean rating of each surgical subtask was evaluated. In respect to the side-by-side comparison of five surgical subtasks, the mean rating of EDS was significantly better than for EG2 (4.4 ± 0.5 LP vs. 3.4 ± 0.6 LP; p = 0.016). Across all 13 surgical subtasks performed with EDS the mean rating was 4.4 ± 0.6 LP. The medians of each Likert item for EDS and EG2 of the intraoperative questionnaire are plotted in a spider chart in Figure 5(a). The median for EDS was at least 4 LP. In contrast, EG2 achieved 4 LP or more for only six Likert items.

Figure 4. Overall performance on a 5-point Likert scale of the Erbe Dissector (EDS; points) and ENSEAL G2 (EG2, diamonds) across surgical subtasks. Mean ± SD.

Figure 5. Intraoperative (a) and postoperative (b) performance aspects (median) for the Erbe Dissector (EDS; short-dashed line) and ENSEAL G2 (EG2; long‑dashed line) by four operators. 5 =Very good; 4 =Good; 3 =Neutral; 2 =Poor; 1 =Very poor.

Postoperative questionnaire

The results of the postoperative questionnaire are plotted as a spider chart in Figure 5(b) showing the medians of each Likert item. Each question was answered by each operator (n = 4) for both instrument types except for the questions ‘Precise dissection’ (EDS n = 3, EG2 n = 2) and ‘Surgical smoke (smell)’ (EDS n = 4, EG2 n = 2). The median for EDS was higher than or equal to that for EG2 except for the question ‘Surgical smoke (smell)’. For all aspects except for the smell of surgical smoke.

Discussion

In past years, many energy-based devices have been tested and proven to facilitate dissection, sealing and cutting in open and laparoscopic procedures [16,17]. Here, we evaluate and describe the newly developed EDS devices and the accompanying new dedicated EDS generator mode.

Appropriate vessel sealing is crucial for patient safety. The initial vessel sealing success rate for EDS was 92% for both the ex vivo and the in vivo setting and no differences were found between arteries and veins. The overall rate of seal failure in vessels up to 7 mm in diameter as observed in previous studies varied extremely among instruments and ranged between zero and 54% [2,7,14,18–20]. The sealing instruments most commonly used in clinical practice have a seal failure rate < 20% [2,7,14,18,19,21]. It has been demonstrated that seal failure rate increases proportionally with vessel diameter [17,20,22]. This is in accordance with our ex vivo results, where the sealing failed in three renal arteries with large diameters of 4.5 mm, 4.7 mm and 5.0 mm, respectively. In our in vivo study sealing failed in two veins with a diameter of 5.4 mm and 7.0 mm and in three arteries with a diameter of 4.3 mm, 5.3 mm and 5.8 mm, respectively, although the success rate was similar when regarding only vessels up to 6 mm. Therefore, in using EDS there is no significant bleeding during dissection, thus facilitating good view.

The median seal and cut time with EDS for all vessels between 2 mm and 6 mm in diameter was 1.6 s in the in vivo experiments and 2.1 s in the ex vivo experiments. This fact means a pronounced time reduction as compared to results previously reported for different devices: sealing time was higher for EG2 (4–8 s) [14,20,23], LigaSure^TM (Medtronic, Dublin, Ireland)(4–5 s) [23,24], BiClamp® (Erbe Elektomedizin) (7–8 s) [24], BiCision® (Erbe Elektromedizin) (8 s) [14], and HARMONIC ACE® (Ethicon Johnson & Johnson) (3–7 s) [18,23]. This can be explained by the unique feature of the electrical blade function of EDS using a combination of cutting and coagulation phases. In fact, reducing sealing time without decreased sealing rate is of major interest not only as an economic factor for operating room time, but also for patient outcome and benefit and for operator comfort.

Considering the experience with previous modes such as the thermoSEAL mode, a correlation between activation time and vessel diameter was expected at least for diameters in the range between 2 and 6 mm [2]. However, no correlation between vessel diameter and activation time was observed for the dedicated EDS mode. This may be due to the fact that the dedicated EDS mode was especially developed and designed to successfully seal larger vessels with diameters of 5 mm. Therefore, the minimum sealing time was sufficient to safely seal most vessels in this study. However, if necessary, the mode can adaptively adjust itself to the tissue properties as was demonstrated by increased activation times for some of the vessels.

The spread of lateral thermal damage and its associated tissue injury still plays a central role when operating in sensitive areas and it is hoped that the developer can minimize this side-effect. Using EDS, lateral thermal damage could be kept to a mean of only 0.8 mm, in contrast to lateral thermal spread between 1.5 mm and 3.3 mm reported by others [2,4,14,18].

The mean burst pressure revealed in the ex vivo bench testing was 1040 mmHg, more than eightfold higher than the physiological mean systolic pressure of 120 mmHg, which speaks for the high safety and quality of EDS and is absolutely comparable with other sealing devices.

This is the first study focusing on the electrical blade function of EDS where operators evaluated the handling and usability. For this purpose, four experienced operators from various disciplines completed an intra- and postoperative questionnaire. Across all surgical subtasks the intraoperative rating of EDS was good to very good, and in the side-by-side comparison, it was better than with EG2.

Every specialist – whether gynecologist, visceral surgeon or thoracic surgeon – had various demands on the device. For instance, feasibility for work in tight spaces for rectal resection and hysterectomy, prevention of lateral thermal damage and optimal precision close to sensitive structures such as small intestine, lung and ureter, safe hemostasis for splenectomy and nephrectomy, precision for working in small steps for lymphadenectomy, optimal blunt dissection with visibility of tissue for vessel sealing and prevention of tissue sticking for all kinds of operations. All of these aspects were intraoperatively rated 4 (good) or 5 (very good) for EDS.

The postoperative questionnaire additionally asked about usability and ergonomics of both tested instruments. The existing standard electrosurgical devices are often inconvenient due to large hand pieces, restricted hand movements, weight and sluggishness, presence of an electrical cord, which may become tangled with other instruments or around the device itself [25]. Long-lasting surgical procedures require numerous activations and are physically exhausting for the operator. Reduction of manual force required to operate the instrument is beneficial. While the manual force in the present study of EG2 was rated very poor (1), it was stated to be very good (5) for EDS. Accessibility of the control elements and ergonomics for EDS were also rated as being superior. Due to the exclusive operation of all functions on the instrument itself, without foot switch, it is possible to operate in an ergonomic posture with a comfortable stand.

Operation time is also influenced by interruptions due to smoke generated by the device. Both devices EDS and EG2 were rated best, namely very good (5) for visibility, which was defined as smoke that did not impair visibility in the operation field.

Conclusions

In conclusion, our results obtained with the ex vivo bench test and the in vivo porcine study show the reliability, safety and efficacy of the newly developed electrosurgical device EDS together with the new dedicated EDS mode. In addition, working speed and lateral thermal damage were judged as best in class and ergonomic aspects such as handling and usability were reported to be good to very good and rated better than EG2.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Karolin Thiel, Markus D. Enderle, Walter Linzenbold, Luca T. Frericks and Ulrich Biber. The operators were Karolin Thiel, Sara Y. Brucker, Bernhard Kraemer and Volker Steger. The first draft of the manuscript was written by Christian Thiel and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Institutional review board statement

The animal study was approved by the Institutional Review Board for animal experiments of the Tuebingen Regional Council, Germany (approval code C01‑17 G in 2017).

Informed consent statement

Not applicable.

Acknowledgments

The authors thank M. Seitzer, A. Stolz, C. Fahrner and T.O. Greiner for their excellent veterinarian and technical assistance and Mary Heaney Margreiter for her kind contribution to preparation of the manuscript.

Disclosure statement

Luca T. Frericks, Ulrich Biber, Walter Linzenbold und Markus D. Enderle are employees of Erbe Elektromedizin GmbH. Christian Thiel, Martin Schenk, Alfred Königsrainer, Sara Y. Brucker, Bernhard Kraemer, Volker Steger and Karolin Thiel have no conflicts of interests or financial ties to disclose.

Supplementary material

The following supporting information can be downloaded at: www.mdpi.com/xxx/s1, Table S1: Number of Likert items and operators for each performance aspect for the Erbe Dissector (EDS) and ENSEAL G2 (EG2)

Data availability statement

The data presented in this study are available on reasonable request from the corresponding author.

Additional information

Funding

This research was funded by Erbe Elektromedizin GmbH, Tuebingen, Germany.