Performance of bipolar forceps during coagulation and its dependence on the tip material: a quantitative experimental assay

Transcription

1 J Neurosurg 100: , 2004 Performance of bipolar forceps during coagulation and its dependence on the tip material: a quantitative experimental assay Technical note TAKESHI MIKAMI, M.D., PH.D., AKIRA TAKAHASHI, M.D., KAZUO HASHI, M.D., PH.D., SHINSEI GASA, PH.D., AND KIYOHIRO HOUKIN, M.D., PH.D. Departments of Neurosurgery and Chemistry, Sapporo Medical University; and Pacific Neurosurgical Consulting, Sapporo, Japan The aim of this study was to measure objectively the adherence of burned tissue to bipolar forceps to evaluate the coagulation performance of forceps made of different types of metals. Coagulation performance of bipolar forceps made of gold, titanium, and stainless steel was determined by comparing the amount of protein in the adhered coagulum on the tips. The amount of adhered coagulum was significantly less on the gold-plated bipolar forceps than on those made of the other two materials. The ease with which coagulum could be removed was compared using the cleaning cycle of an ultrasonic rinsing device. This ease of removal was also significant with the gold-plated forceps. Electron microscopy observations of the surface of the forceps tips revealed a significant difference in roughness among these materials, and there were also significant differences in wetting tensions. Measuring adherence based on three different types of roughness and wetting tensions of forceps made from the same metal (titanium) also demonstrated a significant difference in the cleaning cycle. Histological examination of an artery coagulated with the goldplated bipolar forceps showed that the structure had been completely collapsed without destruction of the layers, whereas arteries coagulated with the other materials revealed severely damaged structures. Adherence to bipolar forceps was dependent on both the material in the tips and the roughness of this material. The gold-plated bipolar forceps demonstrated the best performance. KEY WORDS bipolar forceps gold-plated tip neurosurgical operation B J. Neurosurg. / Volume 100 / January, 2004 IPOLAR coagulation forceps are an invaluable tool for modern neurosurgical operations. 20 Nonetheless, adherence of charred tissue on the the forceps tips and development of an electric spark on coagulation have not been completely eliminated 2 4 and sometimes cause failure of hemostasis or damage to surrounding tissue. 19 The most important factors in bipolar coagulation are the characteristics of the forceps tips and the coagulation device. Electrical or thermal characteristics of the coagulation device and the physical properties of the tip materials have been previously studied. 6,9,12 Several methods to ameliorate problems have been devised, such as temperature control at the tips, 18 use of a heavy metal as the tip material, 10 Teflon coating on the tips, or an automatic coagulation control. 2 There have been many improvements in forceps irrigation as well, such as irrigating with saline 7,13,14 or nonelectrolytic solution. 16 Although even irrigation is indispensable, excessive irrigation prevents coagulation; thus, it is important to make an appropriate dry field during hemostasis. Accordingly, a stabilized state and chemically and physiologically optimal bipolar forceps tips are the most that are needed. Because of the lack of an objective method to evaluate adherence itself, however, the effectiveness of any improvements has only been appreciated by the individual user. In this report, we introduce a method of directly assessing the adherence to forceps by ultrasonic rinsing. Using this method, we compared the efficiency of bipolar forceps with a gold-plated tip, a stainless steel tip, and a titanium tip. Given that the chemical nature of each metal differs, we also evaluated the physical qualities of the tips, such as coarseness of the surface and the wetting tension, to the degree that these properties are attributes of adherence. Clinical Material and Methods Three types of commercially available bipolar forceps with 1-mm-wide tips were assessed: tips plated with 50 m gold (KH-2001; Johnson & Johnson K.K., Codman, Tokyo, Japan), tips made of titanium ( ; Johnson & Johnson K.K., Codman), and tips made of stainless steel (KH-2001; Johnson & Johnson K.K., Codman; Fig. 1). The bipolar forceps were washed with deionized water and ethanol before starting coagulation, and were then dried at 50 C. Coagulation was performed with a Malis bipolar coagulator (CMC III; Codman & Shurtleff, Inc., Raynham, MA). Assessment of Adherence We used whole blood from humans for evaluation of adherence, because in clinical situations most of the coagulum 133

2 T. Mikami, et al. FIG. 1. Photograph depicting bipolar forceps with gold-plated (upper), titanium (center), and stainless steel tips (lower). adhering to the tips of bipolar forceps is blood. One hundred microliters of whole blood preincubated at 37 C was put on a glass slide. The tips of bipolar forceps were placed in the blood, with a gap of 1 mm. Coagulation was performed at constant electric power (15 Malis units, 1.6 W) for 8 to 24 seconds or at varying electric power for a constant time period (8 seconds). After coagulation, the adhered coagulum was removed from the tips by using an ultrasonic processor in a solution of 5 ml of 1% Triton-X 100. The protein content of the solution was assayed by a bicinchroninic acid protein assay reagent (Pierce, Rockford, IL) by using bovine serum albumin as a standard. The reagent was added to 0.1 ml each of standard or coagulated sample, mixed well, and incubated at 37 C for 30 minutes. The absorbance of 562 nm in each tube of the sample was measured and compared with the water reference. Coagulation at each condition was repeated five times, and the amount of coagulum was expressed as the average milligrams of protein in these five procedures. Adherence of coagulum to the forceps tips was assessed by measuring the ultrasonic irrigation time necessary to remove the coagulum. Coagulation of the blood was conducted at 15 Malis units (1.6 W) for 20 seconds. The tip with adhered coagulum was held in 5 ml of 1% Triton-X 100 at a distance 5 mm from the ultrasonic processor, and rinsing was performed (output 2 W). The time it took to detach the adhered coagulum was averaged for 10 procedures and expressed in seconds. Physical Properties of Forceps Tips The surface roughness of the tips was measured by a laser scanning electron microscope (1LM21W; Lasertec, Yokohama, Japan). Two-dimensional z-axis images and threedimensional images were obtained in addition to the usual scanning electron microscopic images. From these electron micrographs, the average roughness (Rz) was calculated at 10 points. This value was the sum of two averaged values: FIG. 2. Upper: Graph demonstrating the amount of protein in the coagulum and the duration of coagulation time. Values represent the average of five coagulation procedures. The amount of protein was significantly lower on the gold-plated forceps tips. *p Lower: Graph demonstrating the amount of protein in the coagulum and the strength of electricity. Values represent the average of five coagulation procedures. The amount of protein was significantly lower on the gold-plated forceps tips. *p Yp, the average height of the five highest peaks from the average plane; and Yv, the average depth of the five lowest ravines from the average plane. Note the following equation: Rz ( m) = ( Yp1 Yp2 Yp3 Yp4 Yp5 5) ( Yv1 Yv2 Yv3 Yv4 Yv5 5), where Yp1 through Yp5 are the five highest peaks from the average plane and Yv1 through Yv5 are the five lowest ravines from the average plane. After the electron microscope analysis, measurement of the wetting tension was undertaken. Originally, although it is the index used for the measurement of plastic wetting tension, this same index was applied to the measurement of the metal wetting tension in this study. A 1-cm 2 metal sample of each material used in the forceps tips was prepared prior to measuring the wetting tension. The wetting tension of each tip material was measured using the Japanese Industrial Standards method (Wako, Tokyo, Japan). 11 Measurement was conducted in an atmosphere of 50% humidity and a temperature of 23 C. The fluid mixture for the test was expanded to the degree that it formed a thin layer on the metal sample by using an applicator. We determined that it was wetting when the fluid remained as a film for more than J. Neurosurg. / Volume 100 / January, 2004

3 Material differences in bipolar forceps seconds before dispersing. In the event that it was not wetting, the test was again applied using another fluid mixture with a higher surface tension. The wetting tension was selected based on the fluid mixture that could consistently maintain this film for 2 seconds. Measurement was repeated three times with each type of material. To determine the degree to which variations in roughness and wetting tension are attributable to bipolar coagulation, we prepared three titanium bipolar forceps tips with different roughnesses and wetting tensions by grinding (#1, #2, #3): #2 is the same sample as previously used for measurement and #3 is so-called mirror finished. Measuring adhered coagulum and assessing adherence of the coagulum was performed according to the aforementioned methods. The size of the tips was 1 mm, and the values of roughness and wetting tension of the tips were as follows: Rz was m in #1, m in #2, and m in #3. The wetting tension was 60 mn/m in #1, 56 to 58 mn/m in #2, and 50 to 52 mn/m in #3. Both Rz and wetting tension of these were significantly different from each other. Histological Examination of the Coagulated Artery Male and female Wistar rats weighing between 320 and 360 g (mean 345 g) were anesthetized intraperitoneally with a mixture of ketamine chlorohydrate (100 mg/kg) and diazepam (2.5 mg/kg) and maintained with spontaneous ventilation. The femoral arteries on both sides were exposed by placing a piece of surgical glove beneath them. Proximal and distal ligature were made using 8 0 nylon thread to reduce the influence of blood flow. The vessel was held manually by closing the bipolar forceps, and coagulation was performed at a setting of 15 Malis units (1.6 W) for 5 seconds. After the bipolar forceps were slowly separated from the blood vessel, the coagulated artery was resected axially. The central part of the coagulation was studied histologically by staining with H & E and orcein to compare the difference in damage. Coagulations were repeated 10 times with each type of forceps tip. Statistical Analysis Data are expressed as the means standard deviation. Correlations were calculated using two-factor factorial analysis of variance. Values related to the roughness of the tip surface and the time to remove the adhered coagulum were analyzed using the Mann Whitney U-test. Histological characteristics were assessed using the Fisher exact test. The level of statistical significance was a probability value less than Results Coagulum Adherence Adherence of coagulum to the bipolar forceps tips during coagulation was compared among the three types of forceps. The amount of adhered coagulum expressed by its protein content increased with a longer coagulation time (Fig. 2 upper). The adhered coagulum was significantly smaller on the gold-plated bipolar forceps tips (p ). A similar relationship was found with varying electrical output. Again, the gold-plated bipolar forceps tips J. Neurosurg. / Volume 100 / January, 2004 FIG. 3. Bar graph demonstrating the time for removal of coagulum by ultrasonic rinsing. Values represent the average of 10 procedures. There are significant differences in time among the various materials tested. *p were associated with the least amount of adhered coagulum (p ; Fig. 2 lower). The mean ultrasonic irrigation time to remove the adhered coagulum varied according to the tip material (Fig. 3). The mean time for coagulum removal from the goldplated tips ( seconds) was significantly shorter (p = ) than that for the stainless steel tips ( seconds). There was also a significant (p = ) difference in the time required for coagulum removal from the titanium tips ( seconds). Physical Properties of Forceps Tips Electron micrographs of the tip surfaces are featured in Fig. 4. The surface of the gold-plated tips is the smoothest among the three materials examined in the two images from the laser microscope, the two-dimensional z-axis image, and the three-dimensional image. Mean Rz values of three samples were significantly different for each material (p = 0.002): m in the gold-plated forceps, m in the titanium forceps, and m in the stainless steel forceps (Fig. 5). The average wetting tension of three samples of each material differed: 48 to 50 mn/m for the gold-plated tip, 56 to 58 mn/m for the titanium, and 60 to 62 mn/m for the stainless steel. Measurement of adherence based on three varieties of roughness on the tips made from the same material (titanium) was as follows. There was no significant difference in adhered coagulum when varying either coagulation time or electrical output. The mean time for removal of coagulum from #1 ( seconds) was significantly shorter than that for #3 ( seconds; p = ; Fig 6). There was also a significant difference in the times between #2 ( seconds) and #3 (p = 0.014). There was no significant difference between values for #1 and #2. Histological Study of the Coagulated Artery The adventitia of the arteries coagulated with the goldplated bipolar forceps were homogeneously thickened and condensed. The tunica media and the internal elastic laminae of the arteries were completely collapsed, and the inter- 135

4 T. Mikami, et al. FIG. 6. Bar graph demonstrating the time for removal of coagulum by ultrasonic rinsing. Values are the average of 10 procedures. There are significant differences in time between #1 and #3 and between #2 and #3. *p nal elastic laminae were preserved (Fig. 7 upper). In contrast, 50% (five cases) of the arteries coagulated with the stainless steel forceps were severely destroyed (Fig. 7 lower). Histologically, there were more variations in the arteries coagulated with the stainless steel forceps than with the gold-plated forceps (p = ). With the titanium forceps, 20% (two cases) of the arteries were found to be histologically destroyed. FIG. 4. Electron micrographs of the surfaces of the bipolar forceps tips. Three-dimensional images of sections of a gold-plated tip (upper), a titanium tip (center), and a stainless steel tip (lower). The surface of the gold-plated tip is smoother than the surface of the stainless steel tip. FIG. 5. Bar graph revealing the value of Rz ( m). Values are expressed as the means standard deviation. Note the significant differences among the three materials. *p Discussion The characteristics of tip material that theoretically influence tissue adhesion on bipolar coagulation include heat and electrical conductivity, ionization tendency of metals, electrical distribution on the tip surface, and the wetting tension of the material. Bipolar coagulation produces heat that causes denaturation and aggregation of protein. Too much heat at the tips causes severe protein destruction and carbonization. When the heat and electrical conductivity are high, the heat in the tips is quickly dispersed to prevent a rise in temperature and overcoagulation. Jacques, et al., 10 suggested coating the forceps tips with heavy metal to increase heat transfer to prevent tissue adherence. Irrigation of the forceps on coagulation may reduce the heat. To use a high heat conductive metal is another way to avoid heat production. Gold has a higher heat conductivity (0.75 cal/cm/sec/ C) than stainless steel (0.04 cal/cm/sec/ C) and titanium (0.02 cal/cm/sec/ C). It also has a higher electrical conductivity (76%/Cu) than stainless steel (2.4%/Cu) and titanium (3.1%/Cu). To plate the forceps tips with gold is therefore an appropriate method to prevent adherence. 8 Metals that have a high ionization tendency, like stainless steel and iron, easily cause oxidation and react more easily with proteins as temperatures rise. The use of silver in some instruments may prevent burning of tips, 15 but silver has a high ionization tendency and oxidizes easily. The ionization tendency of gold is the lowest. The roughness of the surface of the tips contributes to adherence not only by physical properties, but also by nonuniform electrical distribution because the electric current runs 136 J. Neurosurg. / Volume 100 / January, 2004

5 Material differences in bipolar forceps FIG. 7. Upper: Axial photomicrograph of the central part of the femoral artery coagulated with the gold-plated bipolar forceps at 1.6 W for 5 seconds. The internal elastic laminae of the arteries were completely collapsed but preserved. Lower: Axial photomicrograph of the central part of the femoral artery coagulated with stainless steel bipolar forceps at 1.6 W for 5 seconds. Histological damage was more severe than that in the upper image. Orcein, original magnification 20 (upper), 100 (lower). from peak to peak of the spikes on the surface material of the tips on coagulation. Although coagulation performance is mostly influenced by the chemical nature of the metal, it is also influenced by the physical characteristics of the forceps surface. In our study, mirror-finished titanium (#3) may have an advantage in the cleaning cycle of adhered coagulum, but it may easily become roughened by daily washing. In contrast, the gold-plated bipolar forceps have a J. Neurosurg. / Volume 100 / January, 2004 very smooth structure, as was found in our electron microscopy observations. We applied the standard method for evaluating plastic films 11 to assess these metal surfaces. A higher wetting tension of the material makes it easier for coagulum to adhere. Teflon has characteristics not to adhere to other materials and the wetting tension is low. Ceviker, et al., 5 reported that a Teflon-coated bipolar coagulator reduced adherence. Tef- 137

6 T. Mikami, et al. lon cannot be used to cover the entire surface of the forceps, however, given its low electric conductivity, so that Tefloncoated bipolar forceps have nonconducting coated parts and uncoated conducting parts. Also, Teflon comes off easily because of its poor surface tension. Soaking in Mannitol solution also reduces the coefficient of wetting tension between the tissue and the tips of the bipolar forceps. 1 The wetting tension of gold is significantly lower than that of titanium and stainless steel. Structural uniformity after coagulation may be an important factor for safe and consistent coagulation. Siegel and Dunn 17 suggested that heat first produces connective tissue coagulation while preserving the structures. Afterward, amorphous coagulation and finally complete disintegration of the tissue ensues. In our study, the histological changes on coagulation were more variable with titanium and stainless steel bipolar forceps than with gold-plated bipolar forceps. Uneven currents at the tips of the nonplated bipolar forceps may have caused this variability due to their rough surface. The estimated cost is approximately 198,000 for goldplated forceps, 188,000 for titanium forceps, and 160,000 for mirror-finished forceps. The actual selling price for the three different materials is very similar. Conclusions Among the bipolar forceps examined in this study, the gold-plated bipolar forceps showed a minimal tendency for adherence of tissue on coagulation and produced the most uniform histological changes on coagulation. Needless to say, the chemical characteristics and physical properties of the bipolar forceps tips are involved in coagulation performance. Disclaimer None of the authors has a financial interest in the bipolar forceps used in this study. Acknowledgments We thank Tomohiko Asahara, Ph.D., and Fumitaka Kumagaya of Johnson & Johnson K.K., Codman, for their helpful discussions during the preparation of the manuscript, and Naoko Mikami for her technical assistance. References 1. Beatty RM: Prevention of char adherence to bipolar diathermy forceps tips. J Neurosurg 84:540, 1996 (Letter) 2. Bergdahl B, Vallfors B: Studies on coagulation and the development of an automatic computerized bipolar coagulator. Technical note. J Neurosurg 75: , Caffee HH, Ward D: Bipolar coagulation in microvascular surgery. Plast Reconstr Surg 78: , Casotto A, Piattelli M: A new device for electrocoagulation of small vessels. Acta Neurochir 71: , Ceviker N, Keskil S, Baykaner K: A new coated bipolar coagulator: technical note. Acta Neurochir 140: , Dujovny M, Dujovny N, Gundamraj NR, et al: Bipolar coagulation in neurosurgery. Surg Neurol 49: , Dujovny M, Vas R, Osgood CP, et al: Automatically irrigated bipolar forceps. Technical note. J Neurosurg 43: , Edelman ER, Seifert P, Groothuis A, et al: Gold-coated NIR stents in porcine coronary arteries. Circulation 103: , Greenwood J Jr: Two point coagulation. A new principle and instrument for applying coagulation current in neurosurgery. Am J Surg 50: , Jacques S, Bullara LA, Pudenz RH: Microvascular bipolar coagulator. Technical note. J Neurosurg 44: , Japanese Industrial Standards Committee: Plastics-Film and Sheeting-Determination of Wetting Tension. Tokyo: Japanese Standards Association, 1999 pp Lee JY, Ebel H, Balogh A, et al: Comparison of a new automatically controlled electrocoagulator (Valleylab NS 2000-iNSTANT RESPONSE technology) with a high-frequency coagulator. Minim Invasive Neurosurg 42: , Malis LI: Electrosurgery. Technical note. J Neurosurg 85: , Ohta T, Funatsu N, Kuroiwa T, et al: Bipolar diathermy forceps with automatic irrigation. Technical note. J Neurosurg 62: , Ohta T, Kuroiwa T, Kajimoto Y: New bipolar diathermy forceps with automatic dripping and flushing technical note. Neurol Med Chir 39: , Sakatani K, Ohtaki M, Morimoto S, et al: Isotonic mannitol and the prevention of local heat generation and tissue adherence to bipolar diathermy forceps tips during electrical coagulation. Technical note. J Neurosurg 82: , Sigel B, Dunn MR: The mechanism of blood vessel closure by high frequency electro-coagulation. Surg Gynecol Obstet 121: , Sugita K, Tsugane R: Bipolar coagulator with automatic thermocontrol. Technical note. J Neurosurg 41: , Vallfors B, Erlandson BE, Hansson HA, et al: Current leakage in bipolar electrocoagulation. Neurosurgery 13: , Vallfors B, Erlandson BE, Wieck BO, et al: Coagulation in neurosurgery. Acta Neurochir 55:29 34, 1980 Manuscript received April 3, Accepted in final form September 8, Address reprint requests to: Takeshi Mikami, M.D., Ph.D., Department of Neurosurgery, Sapporo Medical University, South 1 West 16, Chuo-ku, Sapporo , Japan. tmikami@ sapmed.ac.jp. 138 J. Neurosurg. / Volume 100 / January, 2004