Objective
Analyze energy-induced damage to the swine vagina during laparoscopic hysterectomy.
Study Design
Laparoscopic colpotomy was performed in swine using ultrasonic, monopolar, and bipolar energy. Specimens (n = 22) from 13 swine were stained with hematoxylin and eosin and Masson’s trichrome for energy-related damage. The distal scalpel-cut margin was used as reference. Energy induced damage was assessed by gynecologic and veterinary pathologists blinded to energy source.
Results
Injury was most apparent on Masson’s trichrome, demonstrating clear injury demarcation, allowing consistent, quantitative damage measurements. Mean injury was 0 ± 0 μM (scalpel, n = 22), 782 ± 359 μM (ultrasonic, n = 7), 2016 ± 1423 μM (monopolar, n = 8), and 3011 ± 1239 μM (bipolar, n = 7). Using scalpel as the reference, all were significant ( P < .001).
Conclusion
All energy sources demonstrated tissue damage, with ultrasonic showing the least and bipolar the greatest. Further study of tissue damage relative to cuff closure at laparoscopic hysterectomy is warranted.
Total laparoscopic hysterectomy (TLH) and robotic-assisted laparoscopic hysterectomy (RALH) are rapidly expanding methods of hysterectomy. Various energy sources have been developed to effect amputation of the cervix from the apex of the vagina including ultrasonic energy (Harmonic Scalpel; Ethicon, Somerville, NJ), bipolar energy, and monopolar energy. These methods are in contrast to transvaginal and abdominal hysterectomies in which removal of the cervix from the vagina is typically accomplished with a scalpel or scissors. If energy is used during abdominal or transvaginal colpotomy, it is generally for the cutting effect, as other methods of obtaining hemostasis, such as suture, can be easily used, thereby minimizing the amount of energy necessary. During a TLH, energy is generally used for cutting and hemostasis when dividing the cuff. Because of the well vascularized, fibromuscular nature of the vagina, it is frequently necessary to slowly divide these tissues to achieve hemostasis, resulting in long instrument activation times. This longer activation time theoretically results in a wider field of adjacent tissue injury when compared with hysterectomies that do not use energy sources, or use them to a lesser degree.
Current data suggest that the rate of vaginal cuff dehiscence is increasing, largely because of its notably higher incidence in laparoscopic and robotic hysterectomy ( Table 1 ). There are little data exploring the reasons for the increased incidence of dehiscence, but it is perhaps because of the expanded use of energy sources in these minimally invasive surgical modalities. The wider field of tissue injury from use of energy for cutting and hemostasis may subsequently reduce suture holding strength, leading to separation of the cuff. If this is true, then the source of energy used for colpotomy may be a variable affecting tissue strength in the vagina. This effect may be magnified if the cuff is closed endoscopically as magnification may lead to sutures being placed closer to the vaginal cuff edge than would occur under direct visualization. Unfortunately, there is no direct evidence to support this theory and it is unknown whether energy-associated tissue damage contributes to evisceration and/or mesh exposure.
| Variable | Agdi | Hur | Kho | Jeung | Persson | Roman |
|---|---|---|---|---|---|---|
| LH | 1.1% | – | – | – | – | 0.7% |
| TLH | – | 4.9% | – | 1.2% | – | – |
| TAH | 0.1% | 0.1% | – | – | – | – |
| TVH | 0.1% | 0.3% | – | – | – | – |
| RALH | – | – | 4.1% | – | 6.3% | – |
The swine has shown to be a useful model for studying minimally invasive surgery. The swine vagina is much larger than smaller animal models, such as the rat and rabbit, allowing easier surgical manipulation, realistic surgical modeling, and more testing to be performed per specimen. Furthermore, the swine is a better model for approximating human skin and tissue healing as studies have demonstrated that small animals heal primarily through wound contraction, as opposed to humans and swine that heal via reepithelialization. In addition, porcine dermal collagen is biochemically similar to human collagen. Although tissue strength and healing have been studied in the swine, the tissues studied were primarily abdominal skin, spleen, bladder, and intestine. In these organs, tissue injury is generally least with scalpel, followed by ultrasonic and bipolar energy, with monopolar energy having the most widely dispersed collateral tissue injury.
The objective of this study was to assess the degree of energy-related injury in the swine vagina after performance of a TLH.
Materials and Methods
This study was approved as an amendment to a comprehensive research and educational investigation involving the Telerobotics and Minimally Invasive Surgery (TAMIS) program at the Uniformed Services University of the Health Sciences (USUHS). The TAMIS protocol uses swine as a teaching model for laparoscopic and robotic surgery. The TAMIS protocol is approved by the USUHS Institutional Animal Care and Use Committee (IACUC) and all study-related procedures are performed at the USUHS Laboratory Animal Medicine Division.
As a component of the protocol, robotic surgical training was conducted on individual fully anesthetized Yorkshire swine that were euthanatized after the training protocol was completed. The vagina was then transected with monopolar cautery, bipolar cautery, or ultrasonic energy. This was performed with traditional laparoscopic instruments, while using the robotic camera and graspers ( Figure 1 ) . Monopolar energy was delivered with closed endoshear tips using 50 W of cutting power. The bipolar was set at 35 W with a blend of 20% cut and 80% coagulation in the cut mode (default setting). Either a Bipolar PKS Plasma J-Hook or a PKS Lyons Dissecting Forcep (Gyrus, Southborough, MA) was used for the bipolar procedure. Ultrasonic energy was provided via the Harmonic Scalpel (Ethicon) with the back of the active blade used for dividing tissue at the maximum power setting of 5. The amputated proximal vagina and uterus were then removed via a previously-placed port. The distal portion of the specimen was cut with a scalpel approximately 2-3 cm from the cauterized edge. The scalpel-cut end was stained with ink (marking the reference end) and the cauterized end was left unmarked. The harvested sections of vagina were maintained as a straight luminal structure during the fixation process by placing an intraluminal insert ( Figure 2 ) . The tissue was fixed in 10% buffered formalin. After fixation, each cylindrical segment was transected longitudinally creating segments containing both the energy-affected tissue and opposite scalpel-incised end on the same tissue specimen. The tissue sections were embedded in paraffin for subsequent slide preparation.
Standard 4 μm histologic slides were prepared and stained with hematoxylin and eosin (H&E) and Masson’s trichrome. Each slide was interpreted by a board certified gynecologic pathologist (C.Z.) and a board certified veterinary pathologist (E.L.); both were blinded to the energy source. For each slide the extent of injury (detailed below) was measured microscopically. The scalpel-cut side of each specimen was considered the control.
Tissue damage was assessed histologically, and the degree of injury was established microscopically based on a qualitative evaluation of the tissue and then was measured using the degree of magnification and internal cellular features as a basis for distance. Injury was measured from the point of energy transection to the nearest point that normal tissue was apparent ( Figure 3 , A) . Criteria demonstrative of electrosurgical tissue injury have been summarized in a retrospective analysis of tissue injury in animal models in which the effects of bipolar and monopolar injury was assessed. Importantly, this analysis described histologic effects as assessed with H&E staining. Generally, those regions most proximal to the energy source will demonstrate coagulative necrosis, associated with denaturation of proteins, desiccation, and loss of normal architecture ( Figure 4 , B) . In affected tissues, vacuoles created by vaporization of cellular fluids and degenerative changes within the cytoplasm will be apparent. As the distance from the energy source increases, tissue damage becomes progressively more subtle, with tissues (particularly muscle) beginning to regain the same staining characteristics as normal tissue. Subtle changes of less damaged tissue may also include pale staining cytoplasm and smaller, darker nuclei. In lower-temperature areas (ie, regions distal to the point of energy), focal hemorrhage into surrounding tissue may be visualized, likely because of microvascular damage. In addition, vascular thrombi may be found in lower-temperature areas. Although neutrophilic infiltration has also been described in the literature, our study obtained samples immediately after euthanasia (within 10 minutes) and as such, injury was too acute for a neutrophilic inflammatory response to be mounted and mobilized to the areas of injury.
