A Comparison of Monopolar Electrosurgery to a New Multipolar Electrosurgical System in a Rat Model

The Laryngoscope Lippincott Williams & Wilkins, Inc., Philadelphia © 2001 The American Laryngological, Rhinological and Otological Society, Inc.

A Comparison of Monopolar Electrosurgery to a New Multipolar Electrosurgical System in a Rat Model Suchet Chinpairoj, MD; Michael D. Feldman, MD, PhD; James C. Saunders, PhD; Erica R. Thaler, MD

Objectives/Hypothesis: The purpose of this study is to compare collateral tissue damage and wound healing in incisions created by electro-dissociation and conventional electrosurgery. Conventional electrosurgery has been used as an alternative to the scalpel to improve hemostasis. However, the heat generated by this instrument can cause tissue damage surrounding the incision, limiting its use around nerves and large blood vessels. A new technology, Coblation (Arthrocare Corp., Sunnyvale, CA), uses “electro-dissociation” to achieve similar results by creating charged particles from a conductive medium to make an incision while simultaneously achieving hemostasis. This new approach to electrosurgery may reduce soft tissue damage. Study Design: Methods: Two prospective, matched design experiments were performed. In experiment I, both devices were set at the same electrical power in watts and then used to create an incision on the tongue of rats. In experiment II, the electrical power settings of both devices were adjusted until they created incisions of the same size. Epithelial destruction and collateral tissue damage were measured in histologically prepared tissue in both experiments, and the wound healing process was observed in experiment II at 0, 3, 7, and 14 days after surgery. Results: The results showed that the electro-dissociation method created significantly less epithelial destruction and collateral tissue damage in both experiments. Granulation tissue formation was also significantly less extensive in the electrodissociation–induced incision after 7 and 14 days of recovery. Conclusions: Wound healing may be faster than with conventional electrosurgery if the Coblation device is used. Key Words: Coblation, electrosurgery, electrodissection. Laryngoscope, 111:213–217, 2001 Presented at the Meeting of the Eastern Section of the American Laryngological, Rhinological and Otological Society, Inc. Pittsburgh, Pennsylvania, January 2000. From the Departments of Otorhinolaryngology (S.C., J.C.S., E.R.T.) and Pathology (M.D.F.), University of Pennsylvania, Philadelphia, Pennsylvania. Supported by a grant from the ArthroCare Corporation. Editor’s Note: This Manuscript was accepted for publication November 2, 2000. Send Correspondence to Erica R. Thaler, MD, Department of Otorhinolaryngology, 5 Silverstein, 3400 Spruce Street, Philadelphia, PA 19104, U.S.A.

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INTRODUCTION Conventional electrosurgery has been clinically available for more than a half century and today is in widespread use as an alternative to the scalpel to reduce bleeding during surgery. The mechanism of electrosurgical cutting is well described elsewhere.1–10 Efforts have been made to reduce surrounding tissue damage created by heat dissipated from the incision. For instance, bipolar electrosurgery allows for a more directed application of current but can only be used for hemostasis. The Coblation device (Arthrocare Corp., Sunnyvale, CA) that was tested in this study uses the electrodissociation method to make an incision. This system consists of two main components: a controller and a probe. The controller is a high-frequency power generator. The probe is composed of electrodes, as shown in Figure 1. All electrodes at the tip of the probe are of the same polarity but electrically insulated from one another. A common electrode is located near the tip of the probe and serves as the return pole for current flow from the individual tip electrodes. By placing the return electrode near the tip of the probe, a ground electrode on the patient’s body is unnecessary. The operating principle of the electro-dissociation method is similar to a conventional electrosurgery system in that a voltage difference is established between the active electrodes and the target tissue. In contrast to conventional electrosurgery, the electro-dissociation method uses an electrically conductive fluid or gel (e.g., isotonic saline or saline gel) in the physical gap between the active electrodes and the target tissue. Both conventional electrosurgery and electrodissociation operate at high frequencies to minimize unwanted tissue stimulation. However, unlike conventional electrocautery generators operating at 350 to 2000 kHz, the generator of electro-dissociation operates at a much lower frequency (100 kHz). There is an increase in the electrical impedance of tissue with decreasing operating frequency. The lower operating frequency of the electrodissociation device means that the impedance to current flow is four to five times greater than that associated with the use of a conventional electrosurgery generator.11 Equally important, the cutting action of the electrodissociation method is also achieved at temperatures of Chinpairoj et al.: Multipolar Electrosurgical System

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tongue was harvested and prepared for histological analysis (see below; experiment II); the animal was killed by an overdose of 100 mg/kg sodium pentobarbital.

Experiment II

Fig. 1. Ablation zone, current path, and conductive irrigant flow of Coblation device.

100°C to 160°C.12 This is lower than the 400°C to 600°C range at which conventional electrosurgery operates. The reduced temperature may also reduce collateral tissue damage from extreme heat. Theoretically, the electro-dissociation method should produce less collateral tissue damage than conventional electrosurgery. The purpose of this study was to test the hypothesis that the electro-dissociation method reduces collateral tissue damage and improves wound healing when compared with conventional electrosurgery methods.

MATERIALS AND METHODS An experimental protocol was designed by the investigators and approved by the Institutional Animal Care and Use Committee of the University of Pennsylvania. Thirty-four Long-Evans male young adult rats weighting 350 to 450 g were used. Six animals were tested in experiment I, and the remaining 28 animals were used in experiment II. The electro-dissociation device, the AccENT head and neck electrosurgery system (model 2000; Arthrocare Corp.), with a single electrode probe and the Valleylab electrosurgery unit (model Force2) with needle electrode were used in this study. The animals were anesthetized with an intraperitoneal injection of 100 mg/kg ketamine hydrochloride and 8 mg/kg xylazine hydrochloride. A mouth retractor was used to keep the mouth open and expose the tongue. A traction suture was placed at the tip of the tongue to provide adequate exposure to make the incision. The handle of the electrosurgery and the electrodissociation probes were mounted on a micromanipulator so that precise positioning could be achieved and also so that no “human error” was introduced. Pressure was applied in such a manner that the tongue muscle was depressed by 2 mm. The currents of both instruments were applied for 3 seconds.

Experiment I Both devices used an equal amount of electrical power to make the incision. Determination of the appropriate settings to use to achieve equivalent power was based on the following equation: Power (watts) ⫽ (Voltage) 2/Resistance (Table I). The setting on the electro-dissociation instrument was adjusted to level 3 in cutting mode, and that on the electrosurgery unit was set to 75 W in cutting mode. These were equivalent power levels. One anterior incision and one posterior incision 8 mm apart from each other were created by electro-dissociation on each side of the tongue. One incision was created by electrosurgery in the middle of the tongue, because of the large size of the incision resultant from this technique. Immediately after the incision was made the

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From pilot work, power settings were identified that produced an incision of equal size for both methods. The setting for electro-dissociation was adjusted to level 8, and the setting on electrosurgery was 17 W in cutting mode. One anterior and one posterior incision, which were 8 mm apart from each other, were created on both sides of the tongue. Electro-dissociation was applied to one side, and electrosurgery to the other. All incisions were allowed to heal by secondary intention to observe the healing process. All of the operated rats were assigned to four groups of seven animals each. One group of animals was killed at each of the following postsurgical intervals: 0, 3, 7, and 14 days. The tongue of each animal was fixed in 10% formaldehyde, embedded in paraffin, cut into 6-␮m-thick serial sections, and stained with H&E. The five sections in the approximate middle of each incision were chosen for measurement and histological analysis. The analysis was performed by a pathologist who was blinded to which lesion was created by electrosurgery and which was created by electro-dissociation. Histological analysis determined the dimension of incision, width of epithelial destruction, area of collagen denaturation, and area of inflammation and granulation tissue formation. Measurements were made using Optimus version 5.23 software. In experiment II, anterior incisions were evaluated separately from posterior incisions because of the differences in the arrangement and density of muscle fibers from the anterior to posterior portion of the tongue. The results were expressed as the mean ⫾ SE. Statistically significant differences between groups were assessed using a two-tailed Student t test for independent samples in experiment I and a two-tailed paired Student t test in experiment II. A P value of .05 or less was considered significant.

RESULTS Experiment I The qualitative macroscopic examination of the incision was performed immediately after surgery. Char was almost undetectable in electro-dissociation but easily seen in the electrosurgery incision. There was white blanching around the incision in both techniques, but less was observed with

TABLE I. Power Comparison Between Electro-dissociation Level and Electrical Power in Watts.* Level of Electro-dissociation

Power (W)

C 1 2 3 4 5 6 7 8 9

14.08 33.33 52.08 75 102.08 133.33 168.75 208.33 252.08 300

1 2 3 4 5 6 7 8 9 10 *Calculation of (voltage)2/resistance.

power

based

on

the

equation:

power

⫽

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the electro-dissociation incision. The width of epithelial destruction and area of collagen denaturation were measured as indicators of collateral tissue damage around the incision. Their mean values are shown in Figure 2. The results revealed that the width and area values were significantly smaller in the electro-dissociation lesion when compared with those produced by electrosurgery (P ⬍.001). It is important to remember that the application of power was the same in both conditions. Photomicrographs of these wounds are shown in Figures 3 and 4.

Experiment II Acute tissue injury. A qualitative macroscopic examination of the incision was performed immediately after surgery. Char was almost undetectable in both groups. The gross appearance of the incision showed white blanching around the wound areas in both groups. Size of incision. Figure 5 shows the mean width, depth, and cross-sectional area of the electro-dissociation and electrosurgery incisions. There were no significant differences in the width, depth, and cross-sectional area of the incisions between the two procedures in both the anterior (P ⫽ .14, P ⫽ .37, and P ⫽ .051, respectively) and posterior (P ⫽ .36, P ⫽ .18, and P ⫽ .38, respectively) locations. Collateral tissue damage. As in experiment I, the width of the epithelial destruction and area of collagen denaturation were measured (Fig. 6). The width of epithelial destruction and area of collagen denaturation were significantly smaller with electro-dissociation than with electrosurgery at both the anterior (P ⫽ .01 and P ⫽ .02, respectively) and posterior (both P ⫽ .01) incisions. Wound healing. Gross infection was not seen in any wound at the time the tissue was harvested. Complete re-epithelialization, as determined by an intact stratum corneum, was noted on the entire histological specimen examined from the electro-dissociation by day 7 and from electrosurgery by day14. The area of inflammation was greatest at day 3 after surgery in both groups (Fig. 7). The mean area of inflammation and granulation tissue was significantly smaller with electro-dissociation

Fig. 2. Comparison of epithelial destruction and cross-sectional area of collagen denaturation for incision made with the electrodissociation device set at level 3 and the electrosurgery unit set at 75 W. Means of the sum are present. Error bars ⫽ standard error; * ⫽ statistically significant difference.

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Fig. 3. Wound produced by conventional electrosurgery on day 0, experiment I.

than with electrosurgery in both anterior and posterior wound locations at day 7 (P ⫽ .03 and P ⫽ .04, respectively) and day 14 (P ⫽ .05 and P ⫽ .04, respectively) (Fig. 7). At day 3, the mean area of inflammation and granulation tissue was significantly smaller in the electrodissociation group (P ⫽ .05) in the anterior wound. The mean area of the posterior wound was 2.39 mm2 with electro-dissociation and 2.30 mm2 with electrosurgery; this result was not statistically significant.

Histology The histological changes may be summarized as follows: Electro-dissociation resulted in an initial thermal burn that, by day 3, had begun re-epithelialization without significant inflammatory cell infiltrate. By day 7, reepithelialization was complete, with resolution of edema (Fig. 8). By day 14, the tissue appeared normal with the exception of a slight increase in the amount of collagen present in the submucosa (Fig. 9). In contrast, electrosurgery resulted in an initial thermal burn with considerably more denatured collagen and a wide area of edema that, by day 3, showed a wide area of

Fig. 4. Wound produced by Coblation on day 0, experiment I.

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Fig. 5. Comparison of depth, width, and cross-sectional area of incision made with the electro-dissociation device set at level 8 and the electrosurgery unit set at 17 W. Means of the sum are present. Error bars indicate SE. These differences did not reach statistical significance.

coagulation necrosis with the beginnings of reepithelialization. At day 7, submucosal inflammatory infiltrate and small capillary ingrowth consistent with granulation tissue were present (Fig. 10). By day 14, the wound had re-epithelialized, but inflammatory cells were still present with edema and granulation tissue (Fig. 11).

DISCUSSION The extent of tissue injury and rapidity of wound healing that followed surgically induced incision on the rat’s tongue was compared using cutting methods of electro-dissociation and electrosurgery. Tissue injury was determined by assessing the macroscopic appearance of the incisions, as well as epithelial destruction and collagen denaturation. Incisions caused by electro-dissociation

Fig. 6. Comparison of epithelial destruction and cross-sectional area of collagen denaturation for incision made with the electrodissociation device set at level 8 and the electrosurgery unit set at 17 W. Means of the sum are present. Error bars ⫽ SE; * ⫽ statistical significance.

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Fig. 7. Comparison of cross-sectional area of inflammation and granulation tissue formation of incision made with electrodissociation device set at level 8 and the electrosurgery unit set at 17 W at each point in time. Incisions at anterior and posterior areas of the tongue are shown separately. Means of the sum are present. Error bars ⫽ SE; * ⫽ statistical significance.

showed less tissue injury lateral to the incision edges than that seen following electrosurgery. Wound healing after injury induced by both devices was evaluated in the substrate and proliferative phases. The process of wound healing may be divided into three phases. The substrate phase, which occurs within the first 3 to 4 days, is characterized by vascular and inflammatory components. The proliferative phase, occurring over the next 10 to 14 days, is dominated by regeneration of epithelium, neoangiogenesis, and proliferation of fibroblasts leading to subsequent synthesis of collagen. The third phase, remodeling, takes place over a period of 6 to 12 months or longer. During this time, the original immature collagen is replaced with a more stable type of collagen.13 In this study, wound healing was assessed by the histopathological examination of re-epithelialization and inflammation and granulation tissue formation at 0, 3, 7, and 14 days after surgery. Wound healing with electro-

Fig. 8. Wound produced by electro-dissociation on day 7, experiment II.

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Fig. 9. Wound produced by electro-dissociation on day 14, experiment II.

dissociation exhibited faster epithelialization and a lesser extent of inflammation and granulation tissue formation than with electrosurgery. Since the initial incisions created by both methods were the same size, these observations suggest that the electro-dissociation incision has faster wound healing than the conventional electrosurgery incision. Ease of use is an important factor in instrument selection. A disadvantage of electro-dissociation is that it requires electrically conductive fluid or gel to fill in the space between the tip of the probe and the targeted tissue. This requires either constant fluid contact or use of a saline gel with the electro-dissociation device, potentially making it more cumbersome to use than conventional electrosurgery. The results of this study indicate that electrodissociation produces less tissue injury and faster wound healing than conventional electrosurgery. Whether this conclusion remains valid with longer recovery times or other tissue sites remains to be seen.

CONCLUSION Electro-dissociation is a technique that provides the surgeon with a new method of tissue dissection. This

Fig. 10. Wound produced by electrosurgery on day 7, experiment II.

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Fig. 11. Wound produced by electrosurgery on day 14, experiment II.

study shows the advantage of electro-dissociation over conventional electrosurgery by demonstrating minimal tissue damage and faster healing in the first 2 weeks after surgery.

Acknowledgment The authors thank Rachael Kurian for her help and support throughout this project.

BIBLIOGRAPHY 1. Honig NM. The mechanism of cutting in electrosurgery. IEEE Trans Biomed Eng 1975;22:58 – 62. 2. Liboon J, Funkhouser W, Terris DJ. A comparison of mucosal incisions made by scalpel, CO2 laser, electrocautery, and constant-voltage electrocautery. Otolaryngol Head Neck Surg 1997;116:379 –385. 3. Carew JF, Ward RF, LaBruna A, et al. Effects of scalpel, electrocautery, and CO2 and KTP lasers on wound healing in rat tongues. Laryngoscope 1998;108:373–380. 4. Tipton WW, Garrick JG, Riggens RS. Healing of electrosurgical and scalpel wounds in rabbits. J Bone Joint Surg 1975;57:377–379. 5. Cochrane JPS, Beacon JP, Creasey GH, et al. Wound healing after laser surgery: an experimental study. Br J Surg 1980;67:740 –743. 6. Keenan KM, Rodeheaver GT, Kenney JG, et al. Surgical cautery revisited. Am J Surg 1984;147:818 – 820. 7. Buell BR, Schuller DE. Comparison of tensile strength in CO2 laser and scalpel skin incisions. Arch Otolaryngol 1983; 109:465– 467. 8. Fisher SE, Frame JW, Vrowne RM, et al. A comparative histological study of wound healing following CO2 laser and conventional surgical excision of canine buccal mucosa. Arch Oral Biol 1983;28:287–291. 9. Luomanen M. A comparative study of healing laser and scalpel incision wounds in rat oral mucosa. Scand J Dent Res 1987;95:65–73. 10. Vogler LJ, Mylrea KC. Tissue heating from electrosurgery signals [Abstract]. In: Proceedings of the 31st Annual Conference on Engineering Medicine Biology. 1978:34. 11. Gabriel S, Lau R, Gabriel C. The dielectric properties of biologic tissues, II: measurements in the frequency range 10 Hz to 20 GHz. Phys Med Biol 1996;41:2251–2269. 12. Rice D, Eggers P, Thapliyal H. Coblation: a novel method for head neck soft tissue surgery. Res Outcomes Otorhinolaryngol 1999;April:1–5. 13. Kanzler MH, Gorsulowsky DC, Swanson NA. Basic mechanisms in the healing cutaneous wound. J Dermatol Surg Oncol 1986;12:1156 –1164.

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