Abstract
Background/Aim: To compare the microscopic, macroscopic and thermal damage inflicted to ovarian tissue by conventional monopolar and bipolar energy, argon plasma coagulation (APC) and diode laser. Materials and Methods: Bovine ovaries were used as a substitute for human tissue and subjected to the four aforementioned techniques and the inflicted damage was measured. Sixty fresh and morphologically similar cadaveric bovine ovaries were divided into five equal groups, each group was subjected to one of the following energy applications for both 1 and 5 s: Monopolar, bipolar electrocoagulation, diode laser, preciseAPC® and forcedAPC®. Ovarian temperatures were measured at 4 and 8 s after treatment. Formalin-fixed ovarian specimens were examined by pathologists regarding macroscopic, microscopic and thermal tissue damage. Results: None of the ovaries reached the temperature producing severe damage (40°C) after 1 s of energy transfer. Heating of adjacent ovarian tissue was least pronounced when preciseAPC® and monopolar electrocoagulation were applied (27.2±3.3°C and 28.2±2.9°C after 5 s of application, respectively). Conversely, 41.7% of the ovaries subjected to bipolar electrocoagulation for 5 s overheated. ForcedAPC® resulted in the most pronounced lateral tissue defects (2.8±0.3 mm after 1 s and 4.7±0.6 mm after 5 s). When the modalities were applied for 5 s, the electrosurgical instruments (mono- and bipolar) and preciseAPC® induced similar lateral tissue damage (1.3±0.6 mm, 1.1±1.6 mm and 1.2±1.3 mm, respectively). preciseAPC® created the shallowest defect of all the techniques (0.05±0.1 mm after 5 s of application). Conclusion: Our study hints at superior safety profiles of preciseAPC® and monopolar electrocoagulation compared to bipolar electrocoagulation, diode laser and forcedAPC® for ovarian laparoscopic surgery.
The fields of electro-, laser and plasma surgery are expanding and the techniques and instruments being used and advanced therein constitute an important part of the modern surgeon’s and gynecologist’s arsenal (1-6). These surgical modalities have to be considered methods of choice for coagulating and cutting in endoscopic/laparoscopic surgery (7-10). This particularly holds true when it comes to operating on delicate bleeding-prone or vital structures underlying pathological lesions, when cost-effectiveness and postoperative pain reduction are crucial factors, and in surgeries in which limiting damage to adjacent structures is of paramount importance (5, 11-15). Since these techniques ensure near-instant vaporization, coagulation and desiccation, bleeding is not a major concern (2, 5, 13, 16). In addition, the destructive force of these instruments is very focused, so that damage to the surrounding healthy tissue is limited (2, 17, 18). Finally, these instruments can use a myriad of application tips and the absence of direct contact between the instrument and the tissue in the case of plasma and laser instruments makes handling and operating in confined spaces easier (5, 19). Soft tissues are usually the preferred substrate (1, 5, 6, 19). Other advantages include the fact that the operator can usually fine tune the energy being applied to the tissue and even use hybrid instruments that can switch between surgical modalities in real time (2, 8, 10, 20).
It is relevant for the purposes of this study to note that tissues (including ovarian tissues) need to be heated to above 42-43°C in order for instantaneous, irreversible thermal damage to occur (21-24). Some authors have considered 45°C to be a more accurate limit in this respect (18). However, lower temperatures (above 37°C but below 42°C) seem to be capable of causing functional or even structural cell damage if applied for sufficiently long (22-24). These are the reasons why contemporary energy-based surgical methods strive to limit energy dissipation to adjacent healthy tissues.
There are several clinically relevant scenarios in which energy-based instruments are used for laparoscopic gynecological surgery which we will briefly discuss in the following paragraphs. Ovarian endometrioma excision and ablation are currently some of the most intriguing and somewhat novel indications for laparoscopic energy-based surgery (25, 26). An ovarian endometrioma presents the clinician with a multifaceted problem. Firstly, one must recognize that patients with endometriosis tend to experience various amounts of pain. sly, it has been shown that ovarian endometrial cystectomies lead to inadvertent damage to healthy ovarian tissue mirrored by reduced anti-Mullerian hormone levels (27-29). Endometriosis recurrence can lead to additional surgeries and even more damage to the ovaries (30). Finally, excision of ovarian endometrioma may have a positive effect in subfertile women aiming for spontaneous inception, but has no proven effect when in vitro fertilization is employed (31). All things considered, most guidelines and experts still suggest that ovarian endometriomas be managed by excision using electrosurgical or classical techniques (25, 31, 32). However, caution is advised when women with fertility issues are considered due to the risk of the depletion of ovarian reserve (25). Thus, the results of some studies imply that energy-based, low-penetration techniques focused on ablation rather than excision can have comparable results in regards to endometrioma recurrence while being superior when it comes to safeguarding the ovarian reserve (26, 33-36).
Laparoscopic ovarian drilling (LOD) was invented as a surgical treatment option for polycystic ovary syndrome in order to reduce the risks of ovarian failure inherent to wedge resection (a technique considered standard for this purpose prior to 1980) (37). Despite a 40%-60% pregnancy rate, as well as a reduction in the percentage of patients with multiple pregnancy and with ovarian hyperstimulation, LOD remains a second-line treatment implemented in clomiphene-resistant patients only (38-41). However, some patients fulfill the surgical criteria for other conditions, such as tubal adhesions and endometriosis, enabling the gynecologist to simultaneously perform LOD. It is crucial to emphasize the importance of energy-based laparoscopic techniques in settings other than LOD.
Energy-based endoscopic surgery is used in a number of other clinical scenarios including extraovarian endometriosis destruction, fibroid myolysis or myomectomy, peritoneal adhesiolysis, and hemostasis after cyst and bleeding-prone cancer resection (42-49). Hysteroscopic polypectomies have also been successfully performed (50).
In this study, we aimed to assess and compare ovarian tissue damage caused by conventional monopolar and bipolar energy, argon plasma coagulation (APC) and diode laser using a bovine model.
Materials and Methods
Since it is ethically and logistically extremely challenging to obtain fresh human ovaries, we used bovine ovaries as a substitute. We opted for bovine ovaries as cows tend to mono-ovulate and their ovaries are very similar in size and in both macroscopic and microscopic morphology to human ovaries (51). Finally, the reproductive physiology of the two species is remarkably similar (51). Thus, we believe that bovine ovarian tissue can approximate its human counterpart well enough to be a valid model for the purposes of our study.
In order to approximate the human ovary, cadaveric bovine ovaries were utilized, being extracted at the slaughterhouse immediately upon the animal’s death. They were then kept on ice until they were thawed at room temperature immediately before being experimented on.
Our measurements were performed at the Department of Gynecology and Obstetrics, University Medical Center Mannheim, Heidelberg University, Mannheim, Germany in February 2021. The study was approved by the Ethics Committee of the Mannheim Medical Faculty of the University of Heidelberg (approval no. 2018-600N-MA, issued September 27, 2018).
Sixty ovaries were divided into five groups (12 ovaries each) and marked per thread labeling at the sample end with 1 s application (see explanation below). The samples were then subjected to the following operative instruments: Group 1: monopolar electrocoagulation (Erbe Elektromedizin GmbH, Tübingen, Germany); group 2: bipolar electrocoagulation (Erbe Elektromedizin GmbH); group 3: Leonardo® YPG diode laser (Biolitec AG, Jena, Germany); group 4: preciseAPC®; and group 5: forcedAPC® (Erbe Elektromedizin GmbH).
A single point on each ovary was treated for 1 s (on the thread-labeled end) and 5 s (on the unlabeled end) by the modality of energy application of its respective group. The energy modalities were applied to the ovarian surface by a single operator, the power source being fixed on a supportive metal apparatus. As only the laser generator offers the option to precisely define an energy application time of below 1 s, only the ovaries subjected to this technique could be treated for precisely 1 s. The values of the other 1-s samples were extrapolated according to the actual duration of the energy application, which was displayed by the generator accordingly. A precise 5-s application was possible using all of the five methodologies.
A monopolar hook tip GK384 (Aesculap, Tuttlingen, Germany) was utilized with the aut°CUT effect 2.4, with peak voltage of 350 V and power limitation of 94 W. A PM438 Maryland fenestrated forceps with an interbranch aperture of 4 mm conducted the bipolar softCOAG effect 3.0, with peak voltage of 125 V and power limitation of 50 W, powered by the VIO® 3 generator. VIO® 3 is a voltage constant-controlled electrosurgical unit. Depending on the tissue impedance, the power output is adjusted to achieve an optimized target tissue effect. The power output cannot exceed a maximum set value. The YPG diode laser was implemented at a 25 W and 980 nm power setting.
The VIO® 3 system (Erbe Elektromedizin GmbH) with an APC 3 plasma surgery module was used to generate and focus argon plasma. The preciseAPC® and forcedAPC® modes were utilized in our experimental setting with a 5 mm distance from ovarian tissue and an APC effect 5 with 3 W power limitation for preciseAPC® and an APC effect 3.0 with 30 W power limitation for forcedAPC® respectively.
The surface pressure for all modalities, barring the laser, was controlled by resetting the Sartorius CPA225D scale to zero (Sartorius Lab Instruments GmbH & Co. KG, Goettingen, Germany).
Tissue temperatures were measured using a HANNA HI8757K thermocouple thermometer with a HI766C1, ultra-fast penetration probe (Hanna Instruments, Woonsocket, RI, USA). The temperatures were measured 1 cm lateral to the application spot at 4 and 8 s after each energy application, aiming for the most relevant temperature change distribution.
After formalin fixation, ovarian specimens were examined by blinded surgical pathologists of the Institute of Pathology, University Medical Centre Mannheim, Heidelberg University, Mannheim, Germany together with surgical gynecologists. Initially, all ovarian specimens were inspected for surface lesions visible to the naked eye. If a lesion was discerned macroscopically, two-dimensional measurements (width and length) were performed using a microcaliper. The pathologist would then proceed to conduct a microscopic examination of all the specimens regardless of their macroscopic appearance. The ovarian specimen was cut into 0.3 cm-thin slices which were subsequently transferred into histocassettes (R. Langenbrinck GmbH Labor- und Medizintechnik, Emmendingen, Germany), assigned to each ovary, subdivided into 1 and 5 s lesions. All embedded specimens underwent automatic tissue processing according to standard protocol utilizing Shandon Pathcentre (Thermo Fisher Scientific, Waltham, MA, USA), followed by manual paraffin embedding. From paraffin-embedded tissue, 2-3 μm slices with a PFM Slide 4004 M microtome (PFM Medical AG, Cologne, Germany) were prepared and mounted on Superfrost microscope glass slides (Epredia, Kalamazoo, MI, USA). The slides were automatically stained according to standard hematoxylin and eosin protocol utilizing Medite Tissue Stainer 720 (Medite Medical GmbH, Burgdorf, Germany) with a mixture of Hemalaun solution I (Dr. K. Hollborn & Söhne GmbH & Co. KG, Leipzig, Germany) and Meyer’s Hemalaun solution (Merck KGaA, Darmstadt, Germany), at a 1:1 ratio, followed by 0.5% aqueous eosin solution (Dr. K. Hollborn & Söhne GmbH & Co. KG, Leipzig, Germany). The hematoxylin and eosin-stained slides were microscopically examined by a surgical pathologist (TG) utilizing a BX46 microscope (Olympus Europa SE & Co. KG, Hamburg, Germany) in order to assess tissue damage by measuring the length and depth of the lesions. An example of microscopic evaluation of damage is shown in Figure 1.
Example of microscopic evaluation of damage. A: Ovarian tissue at 3× magnification. An ovarian follicle can be seen in the upper left corner. The tissue defect is highlighted by the black outline. Yellow bars depict the depth and length of tissue damage after 5 s of diode laser application. B: Higher magnification (40×) of damaged tissue. Ovarian stroma cells are deformed and contain thin, elongated nuclei with thermally condensed chromatin.
Ovarian temperature distributions for each technique were expressed as means and standard deviations. The percentage of the ovaries within each group that surpassed a potentially injurious temperature of 40°C at 1-cm distance from the application spot was noted for both application times, at 4 and 8 s after treatment. This temperature cut-off was chosen for reasons explained in the introduction. Even though there is no unanimous evidence base that this temperature is injurious when applied for such a short period of time, we decided to use this more stringent 40°C cut-off to compensate for slight and expected imprecisions of the instruments used. Temperatures after 1 s application of energy were time-adjusted since only the laser could be configured to transmit its energy to the tissue for exactly 1 s. Finally, the distributions of the length and depth of ovarian lesions made by the various techniques (after both 1 and 5 s application) were expressed as means and standard deviations. We did not try to evaluate whether or not the differences between the instruments were statistically significant because our sample sizes were too small to come to any meaningful conclusions. IBM’s SPSS Statistics software (IBM SPSS Statistics for Windows, Version 23.0., IBM Corp., Armonk, NY, USA) was used for the calculations.
Results
The results of our experiments are presented in Figure 2 and Figure 3. None of the ovaries reached the critical temperature (40°C) after a 1-s energy transfer. Adjacent ovarian tissue heating was least pronounced when the preciseAPC® instrument was used for approximately 1 s. However, this was less clear when the techniques were applied for 5 s. Namely, both preciseAPC® and monopolar electrocoagulation heated the ovaries to a similar degree.
Ovarian temperatures at 4 s (left) and 8 s (right) after a 1 s (A) or 5 s (B) application of different energy-based instruments. *Represent outliers.
Extent of damage to ovarian tissue after 1 s (A) or 5 s (B) application of different energy-based instruments. *Represent outliers.
Ovarian tissue overheating was not observed in any of the ovaries subjected (for 1 or 5 s) to APC or monopolar electrocoagulation. At the other end of the spectrum, 41.7% of the ovaries subjected to bipolar electrocoagulation for 5 s remained overheated even 8 s after the procedure. Equally remarkable is the fact that both 1 and 5 s applications of forcedAPC® resulted in the most pronounced horizontal plane tissue defects but did not heat the adjacent tissue as much as the laser or the bipolar current when applied for an identical amount of time.
forcedAPC® created the largest tissue defects (after both 1 and 5 s of use) of all the energy application modalities, while preciseAPC® produced negligible tissue defects when applied for 1 s. However, when the various modalities were applied for 5 s, the length of the lesions created by electrosurgical instruments (both mono- and bipolar) and the preciseAPC® modality were similar. Moreover, preciseAPC® created the shallowest defect of all the techniques, even after 5 s of application.
Discussion
In recent years, both laparoscopic and energy-based surgery in all constellations have been gaining momentum in the field of gynecology, including but not limited to treatment of endometriosis, ovarian cysts, polyps, adnexectomies and ovarian drilling (7, 52). This is due to a myriad of reasons: Laparoscopic scars are less disfiguring compared to laparotomic scars, these techniques are less painful and seem to be tissue-sparing – particularly important when dealing with ovarian pathology; they offer near-instant reliable hemostasis and they are sometimes a part of hybrid devices that enable the gynecologist to switch between energy application modalities with relative ease (5, 7, 12, 49, 53).
Hendriks et al. found bipolar diathermy to be the most destructive when it comes to ovarian tissue destruction, while the CO2 laser is the most tissue-sparing (51). Conversely, the bipolar electrosurgical equipment we tested was not the most damaging, rather the diode laser was. The different performances of the lasers in our study compared to Hendriks et al.‘s may be explained by the different lasers utilized. Moreover, Hendriks et al. used variable stimulation times when applying bipolar current which may also explain this discrepancy. Monopolar electrosurgical techniques proved uniformly tissue-sparing in both studies. A study by Carus et al. has, like ours, shown that a cold plasma beam is least damaging to tissues (liver tissue in the case of their study) when compared to monopolar and bipolar electrosurgical devices (54).
Our study implies that APC (the preciseAPC® mode in particular) limits collateral heat conduction through ovarian tissue and makes very shallow defects at the application site. This is promising from a safety point of view since the technique does not adversely effect adjacent nontargeted follicles, safeguarding the ovarian reserve. Thus preciseAPC® seems to offer reproducible target tissue effects that are less dependent on the application duration per surface area compared to the other thermal modalities. Based on the results of our study, it seems that APC is rivaled only by monopolar current in these regards but there are indications that these are both superior to the other techniques we analyzed. However, since we did not conduct a rigorous statistical analysis, one cannot claim that these apparent differences are indeed statistically significant. Nevertheless, in our view, the preciseAPC® technology warrants further field testing in real-world clinical scenarios, with ovarian endometrioma ablation being one of the most interesting possible applications (26).
Our study has several limitations. Firstly, the production of smoke and vapor and their elimination from the operative setting are by no means unimportant in vivo. In addition, we used bovine ovaries as substitutes for human ovaries which have been utilized by other investigators before, but remain to be validated as an experimental technique. In vivo experiments will be necessary in order to shed more light on these circumstances. The bovine ovaries were at room temperature before the start of the experiments, which is problematic given that ovaries are at body temperature in vivo. This probably led to an underestimation of the peak ovarian temperatures reached when using the various energy-based instruments. This does not, however, call into question the fact that some techniques utilized in our study were associated with less heating of adjacent ovarian tissue. The study sample was small, thus limiting the generalizability and certainty of its conclusions and therefore our study has a proof-of-principle and hypothesis-generating character. Moreover, tissue loss in vivo may be larger than observed in this study since tissue fixation prevents inflammation. Furthermore, the tissue shrinks because of the fixation, causing the volume of the tissue defect to be underestimated. Conversely, tissue vascularization might aid in reducing damage in vitro, as this could provide a heat-sink effect (51). The fact that the ovaries were kept on ice before being used in the experiments might have also caused some amount of thermal damage, but the damage was conceivably uniform between the ovaries. The balance between these factors is difficult to ascertain at this point and requires further studies.
Conclusion
Our study tried to better define the safety profiles of energy-based instruments in a bovine ovarian model based on macroscopic and microscopic volume defects, as well as potential heat damage to tissues distant from the site of energy application. This experimental concept has proved itself to be feasible and requires further variations of the instrument settings and larger sample sizes in subsequent work.
Footnotes
Authors’ Contributions
Conception and design of the study: S.S., S.B. and B.T. Data collection: S.S., S.B., B.T. and N.F. Data analysis and interpretation: T.G., C.S., M.S., M.N., L.B. and S.S. Responsible surgeon or imager: S.B., T.G. and C.S. Statistical analysis: S.S. and B.T. Article preparation phase 1 - drafting the article: S.S., N.F., T.G. and C.S. Article preparation phase 2 - revising the article critically for important intellectual content: S.B., B.T., M.S., M.N. and L.B. Final approval of the version to be submitted: all Authors.
Conflicts of Interest
N. F. is an employee of Erbe Elektromedizin GmbH. All other Authors have nothing to disclose.
- Received November 29, 2022.
- Revision received December 24, 2022.
- Accepted January 9, 2023.
- Copyright © 2023, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY-NC-ND) 4.0 international license (https://creativecommons.org/licenses/by-nc-nd/4.0).
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