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Tissue actions of bipolar scissors compared with monopolar devices
Vol. 63, No.2, February 1995
FERTILITY AND STERILITY
Printed on acid-tree paper in U. S. A.
Copyright c 1995 American Society for Reproductive Medicine
Tissue actions of bipolar scissors compared with monopolar devices
Michael S. Baggish, M.D. * Robert D. Tucker, Ph.D., M.D.t Good Samaritan Hospital, Cincinnati, Ohio, and University of Iowa, Iowa City, Iowa
Objectives: To establish whether bipolar scissors offer equivalent cutting performance compared with monopolar scissors and to compare extent of thermal coagulation injury using two electrosurgical generators. Design: Eighteen female rabbits' uterine horns were cut using controlled velocity at several different wattages with either bipolar or monopolar scissors. The specimens were examined microscopically and zones of thermal necrosis were measured using a stage micrometer against a 1 mm standard. Results: Bipolar scissors cut equally well compared with monopolar scissors and showed significantly less thermal injury. When coupled to a constant voltage generator both the bipolar and monopolar scissors performed better. Conclusion: Bipolar scissors offer the surgeon significant safety advantages and equivalent or better performance compared with monopolar scissors when used for laparoscopic surgery. Fertil Steril 1995;63:422-6 Key Words: Bipolar scissors, laparoscopic surgery, thermal injury, tissue action, constant voltage electrosurgical unit
The rapid growth and increasing complexity of laparoscopic surgical procedures has accentuated the need for simplified techniques to control bleeding. The essence of least invasive surgery is to operate in a dry field, avoiding major hemorrhage, which can force conversion of the endoscopic approach to a laparotomy. The resurgence of radio frequency electrosurgical devices fulfills the need for tissue cutting with simultaneous vascular coagulation in a relatively simpIe cost-effective manner. Until recently, such cutting tools have used monopolar delivery systems. Bipolar coagulation forceps have been used for many years and have superceded monopolar instruments for the performance of tubal sterilization largely because of safety advantages (1-3). Monopo-
Received May 6, 1994; revised and accepted August 26, 1994.
lar electrodes effect action at the electrode-tissue interface by the creation of high current density (power density), conversion of electrical to thermal energy, and the return of current to ground (via ground plate and electrosurgical generator) using the patient as the intermediary conductor. In contrast, bipolar electrodes are coupled such that one part serves as the active electrode and its mate serves as the neutral (return) electrode. Therefore, current passes only through the tissue held between the jaws of the forceps and not indiscriminately through the body of the patient. The risks of high frequency leakage and dangerous current splitting to ground therefore are minimized (4-6). The application of bipolar technology to effect cutting tissue by means of bipolar scissors is reported herein. This new device was compared with monopolar scissors in so far as hemostasis attained and tissue thermal artifact produced.
* Reprint requests: Michael S. Baggish, M.D., Department of Obstetrics and Gynecology, Good Samaritan Hospital, 375 Dixmyth Avenue, Cincinnati, Ohio 45220 (FAX: 513-221-5865). t Department of Pathology and Biomedical Engineering, University of Iowa. 422
Baggish and Tucker Techniques and instrumentation
MATERIALS AND METHODS
The study was carried out at three centers: Good Samaritan Hospital, Cincinnati, Ravenswood HosFertility and Sterility
pital, Chicago, and The University of Iowa. Eighteen New Zealand female rabbits weighing 5 to 6 kg were anesthetized with 5 mg/kg Rompun 5 mg/kg and 35 mg/kg Ketamine. The animals underwent laparotomy via midline incision; the uterine horns were exposed. The horn was cut into segments using bipolar scissors (left horn) and monopolar scissors (right horn). Ninety-four cuts were made at varying power settings: 25, 30, 35, 40, 45, and 50 W. Each segment was removed and pinned flat to prevent curling. The samples were fixed 24 to 48 hours in 10% buffered formalin. The samples were embedded in paraffin, sectioned, stained with hematoxylin and eosin, and evaluated microscopically. The area of thermal coagulation, i.e., irreversible injury, was measured using an Olympus-Vanox T Photomicroscope (Olympus, Lake Success, NY) with built-in stage micrometer. The units of measurement on the micrometer were calibrated at various objective powers (X4, X10, X20) against a Zeiss and Olympus 1 mm standard (Zeiss, Thornwood, NY), consisting of 100 subdivisions (0.01 mm). Zone of thermal injury (mm) was plotted against applied energy (watts) and statistically analyzed by Wilcoxon and Sign nonparametric methods. Monopolar and bipolar data were compared. Because both sets of data were completely matched, a difference curve was constructed. Specification Scissors
Bipolar scissors were supplied by Everest Medical (Minneapolis, MN). The design of the insulated dual-action scissors consists of stainless steel electrodes bonded opposite to the ceramic cutting surfaces of the two blades. The shaft diameter of the scissors was 5 mm and the working length was 33 cm or 45 cm. Monopolar scissors were supplied by Ethicon Endosurgery (Cincinnati, OH). The 5-mm diameter scissors was curved and insulated to the exposed blades with 0.008- to 0.009-inch (0.200 to 0.225 mm) Teflon. The working length measured 33 cm. The electrodes consisted of stainless steel blades (both cutting and reverse surfaces). Both pieces of equipment were disposable (single use). Specifications of Electrosurgical Generator
Two types of electro surgical generators were used for the experiment. Each is designed to deliver maximum output power into a resistive load of approximately 300 n. Erbe MCC 350 (Erbe, Tublingen, Germany) and Valleylab Force 2 (Valley LaboVol. 63, No.2, February 1995
E
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0.10
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0.40'
~
0.10'
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0.20'
::J: l-
0.10'
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0
(B)
0.10'
0.00'
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II
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411
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15
N APPLIED WATTS
Figure 1 Plot of zones of thermal injury associated with increasing wattage for both monopolar (e; B) and bipolar (A; A) scissors. The delta thermal injury is plotted in C (0).
ratories, Boulder, CO) generators represent two totally different technologies: The Erbe MCC 350 generator exemplifies constant voltage output, with microprocessor technology and peak voltages ranging from 200 to 600 V at the electrode-tissue interface. The generator operates at a frequency 350 kHz and is equipped with bipolar pure sign wave output (cutting current). The ValleylabForce 2 generator is not a constant voltage generator. In bipolar mode, it produces 0 to 800 V open circuit operating at 500 kHz. It is not equipped with automatic bipolar technology. Standardization of Electrosurgical Cutting Velocity
Because thermal damage relates to the duration of electric current on tissue, quantification of cutting velocity was considered important. This was attained by performing a deliberate and exaggerated motion lasting 1 second for each mechanical cutting action of the scissors. In fact, during the experiments, this method of cutting was found to produce the most effective hemostasis. RESULTS
Figure 1 details a plot of zones of damage associated with increasing wattage for both monopolar and bipolar scissors. Monopolar data is shown in curve B, bipolar data is shown in curve A, and the difference between curve B and curve A is shown in curve C. The bipolar data follows a path that closely approximates a straight line from 25 to 50 W. Significantly greater damage to tissue collated with inBaggish and Tucker Techniques and instrumentation
423
> a: :::)
... ~ IL
0
W
Z
0
N
Z C
W
::E
0.11 0.10' D.lI' 0.10' 0.411' 0.40' 0.86 0.10' O.U' 0.20' 0.11' 0.10' O.OS 0.00 20
NOTI!: • DATA
IIIII'~.D
IIY , WATT I'0Il_ C.
OONTIIAIIT IIETWEEN THE • AND 110 .-LOTII
J/././
/1
(C)
,..J.:,/"//
(A)
25
81
80
50
411
40
61
APPLIED WATTS
> a: :::)
... ~ IL
0
W
Z
2
z
C
W
::E
o.e5 0.80' 0.11' 0.10' 0.411' 0.40' 0.86' 0.80' D.25 0.20' 0.11' 0.10' O.OS 0.00 110
Memll .. DATA DI"U._ IIY , WATT 1'011 MIIII OP CONTIIAIT ..,....M .. AND . . PLOTII
I/
•
,.1
(0)
..,-/ /","
;;----'
U
80
81
40
411
50
Iii
APPLIED WATTS
Figure 2 (A), Mean zones of damage created by bipolar (&; A) and monopolar (e; B) scissors. Error bars, 95% confidence intervals. (B), The same data as in A plotted with 2 SD error bars.
creasing applied wattage when time on tissue was held constant (P < 0.001). The monopolar data also showed a strongly significant fit (P < 0.001) to a second order polynomial of increasing thermal damage with increasing wattage. The values for thermal damage at a given wattage were always larger in this curve than they were in the bipolar curve. Curve C illustrates the difference values between the two sets of above data. The equation for this difference has a strongly significant fit (P < 0.001) to a linear function that expresses how much larger the monopolar data is than the bipolar data. The equation is given by Delta = (Mo - Bi) = 1.92 X AW + 0.0001 and clearly states that on the average and at any value of AW, applied wattage, the monopolar data will be about twice as large as the bipolar data. Figure 2A plots mean areas of damage generated by the two scissor types as functions of the applied wattage and is accompanied by an error bar that encompasses the 95% confidence intervals for that mean. Figure 2B plots the same data with two stan424
Baggish and Tucker
Techniques and instrumentation
dard deviation error bars. Figure 3 illustrates the strong correlation between areas of thermal injury induced by the two methods. This plot is misleading in the sense that injury induced by one method is not dependent on injury induced by the second method. However, it clearly illustrates that the use of thermal energy, which is common to both methods, causes similar areas of damage when it is applied by either method. The area of injury caused by a given wattage in the monopolar method is two times as large as that generated by the bipolar method. Of particular interest in this plot is the lack of data seen in the midregion of the plot. Despite the fact that wattages were uniformly increased in 5 W increments, the data do not show a continuous series of points over the area range. This region is identified as the "GAP" region on the plot. Other than larger zones of thermal injury, little benefit could be observed with power settings> 35 W with either bipolar or monopolar modality. Five times less mean thermal injury was observed with the constant voltage-automatic bipolar electrosurgical unit (ESU) compared with the conventional ESU at 25 W. The area of coagulation necrosis was easily identified (Fig. 4A). The outer edge of the zone was marked by a thin line of cellular debris and/or carbonization. The "dead zone," i.e., irreversible injury, was marked by deep blue or purple staining that was in sharp contrast to the light blue uptake of the surrounding viable tissue. Cellular detail was indistinct within the zone (Fig. 4B). Nuclei were
> a:
...~ :::)
0.10
.:
0.50
..
IL
0
0.40'
W
Z
0
N
0.80
c...I
0.20'
::J
a:
0 D. 0 Z 0 :::E
..
.'
GAP
0.10 0.00 0.00
0.05
0.10
0.11
0.20
0.115
0.80
BIPOLAR ZONE OF INJURY
Figure 3 Regression of injury from monopolar versus bipolar scissors. Thermal energy results in similar areas of damage when applied by either method. The area of injury generllted by monopolar scissors at any given wattage is two times greater than that generated by bipolar scissors. b., areas of injury. Monopolar = 1.99(bipolar); n = 30; r = 0.9741.
Fertility and Sterility
pyknotic and bizarrely elongated or smudged. Within the zone and neighboring the zone, blood vessels and lymphatics were thrombosed or collapsed (Fig. 4C). Occasionally vacuoles were created and sometimes filled with proteinaceous fluid. The latter were associated with the more extensive destruction, i.e., >200 JLm (Fig. 4D). Cut modes of the ESU produced sinusoidal outputs. However, the amplitude variations and high frequency components ofthe Valleylab system contrasted to the purely sinusoidal constant voltage output of the Erbe ESU. The Erbe ESU with a frequency of 350 kHz generated more or less pure sinusoidal shape waveforms that were independent of the resistive load or power setting. The Valleylab ESU with a fundamental frequency of 500 kHz produced a waveform that was asymmetric and noisy with several harmonics. DISCUSSION
Several problems are associated with the use of monopolar devices during operative laparoscopy. These include direct coupling, capacitive coupling, and high frequency leakage (4, 5). In an effort to diminish these inherent risks, gynecologists have in the past turned to bipolar technology (6). Until recently, no bipolar cutting devices were available for use during laparoscopic surgery. The bipolar scissors used in this investigation proved to be at least equally efficacious when compared with their monopolar counterparts. With either of the two generators used in this experiment, the areas of thermal artifact were less with bipolar than monopolar scissors. Hemostasis was adequate with both pairs of scissors tested. Because the bipolar technology is not associated with capacitive or direct coupling, they are safer to use with laparoscopic techniques, particularly in situations where peripheral vision is diminished. Although thermal injury can occur with bipolar instruments, those injuries relate to the surgeon picking up the wrong
Figure 4 (A), Section of rabbit horn (X40) showing thin line of carbon formation. Bipolar cut, 30 W. (B), Magnification (X100) showing 0.1 mm necrotic zone (arrows) characterized by deeper staining, distorted nuclei, and cells. The line of carbonization can be seen at the 65 division mark of the micrometer. Bipolar cut, 30 W. (C), Thermal damage measuring 0.34 mm after a 30 W monopolar cut (X40). (D), Magnification (X200) of Figure 3 showing thrombosed vessels (white arrows), elongated bizarre nuclei, and vacuoles containing proteinaceous material (dark arrows). These changes were seen with thermal injury zones> 200 11m. Monopolar cut, 30 W. Vol. 63, No.2, February 1995
Baggish and Tucker
Techniques and instrumentation
425
structure or by conductive spread of heat associated with prolonged time of application. Obviously, the same additional difficulties can happen additively with monopolar instruments as well. Effective cutting of tissue occurs with voltages between 200 and 600. Carbonization and excessive coagulation are reduced when electrode-tissue interface operates at voltages < 600. Unfortunately, conventional generators cannot produce voltages < 600 unless the power is set very low «20 W) creating very slow cutting. Constant voltage generators maintain this preferable peak to peak voltage at <600 V even at high powers, therefore, thermal injury (coagulation necrosis) zones are decreased. When high frequency current flows through constrictions in tissue using monopolar techniques, the thermal action starts at the point of constriction and not at the point where the electrode touches the tissue (decreased area increases current density and thus thermal damage). Thus, the initial flow of current may be outside the field of the operator's view. With bipolar application, the site ofthe thermal action is at the position of electrodes. Coagulation occurs at 70°C whereupon collagens within the clot are converted into glucose, producing an adhesive effect, causing the clot to stick to the electrode. When sticking occurs, the blood vessel and clot are avulsed, reopening the blood vessel, as the electrode is pulled away. Automatic bipolar control based on the change in electrical resistance of the coagulated tissue relative to the temperature of the tissue helps to ensure that the electrode remains clean during cutting and coagulation. Addi-
426
Baggish and Tucker Techniques and instrumentation
tionally, unnecessary long and intensive coagulation increases the risk of accidental burns by conduction. Based on this study one could conclude that bipolar scissors perform competitively with monopolar scissors relative to hemostasis, speed, and secondary thermal injury. Bipolar scissors offer the surgeon and the patient significant safety advantages, particularly when coupled to a microprocessor controlled electrosurgical generator. Acknowledgment. The authors thank Robert Johnson, Ph.D., of the Good Samaritan Hospital Research Department, Cincinnati' Ohio, for performing the statistical tests.
REFERENCES 1. Thompson BN, Wheeless CR. Gastrointestinal complications of laparoscopic sterilization. Obstet Gynecol 1973; 41:669-74. 2. Tucker RD, Benda JA, Sievert CE, Engel T. The effect of bipolar electrosurgical coagulation waveform on a rat uterine model of fallopian tube sterilization. J Gynecol Surg 1992;8:235-41. 3. Tucker RD, Benda JA, Mardan A, Engel T. The interaction of electrosurgical bipolar forceps and generators on an animal model of fallopian tube sterilization. Am J Obstet Gynecol 1991;165:443-9. 4. Baggish MS, Diamond MP, Nezhat C, Rock JA, SanFilippo JS. Overcoming complications of laparoscopic surgery I. Contemp Ob Gyn 1994;39:92-106. 5. Voyles CR, Tucker RD. Education and engineering solutions for potential problems with laparoscopic monopolar electrosurgery. Am J Surg 1992;164:57-62. 6. Baggish MS. Is it necessary to repeat history [editorial]? J Gynecol Surg 1989;5:323.
Fertility and Sterility
FERTILITY AND STERILITY
Printed on acid-tree paper in U. S. A.
Copyright c 1995 American Society for Reproductive Medicine
Tissue actions of bipolar scissors compared with monopolar devices
Michael S. Baggish, M.D. * Robert D. Tucker, Ph.D., M.D.t Good Samaritan Hospital, Cincinnati, Ohio, and University of Iowa, Iowa City, Iowa
Objectives: To establish whether bipolar scissors offer equivalent cutting performance compared with monopolar scissors and to compare extent of thermal coagulation injury using two electrosurgical generators. Design: Eighteen female rabbits' uterine horns were cut using controlled velocity at several different wattages with either bipolar or monopolar scissors. The specimens were examined microscopically and zones of thermal necrosis were measured using a stage micrometer against a 1 mm standard. Results: Bipolar scissors cut equally well compared with monopolar scissors and showed significantly less thermal injury. When coupled to a constant voltage generator both the bipolar and monopolar scissors performed better. Conclusion: Bipolar scissors offer the surgeon significant safety advantages and equivalent or better performance compared with monopolar scissors when used for laparoscopic surgery. Fertil Steril 1995;63:422-6 Key Words: Bipolar scissors, laparoscopic surgery, thermal injury, tissue action, constant voltage electrosurgical unit
The rapid growth and increasing complexity of laparoscopic surgical procedures has accentuated the need for simplified techniques to control bleeding. The essence of least invasive surgery is to operate in a dry field, avoiding major hemorrhage, which can force conversion of the endoscopic approach to a laparotomy. The resurgence of radio frequency electrosurgical devices fulfills the need for tissue cutting with simultaneous vascular coagulation in a relatively simpIe cost-effective manner. Until recently, such cutting tools have used monopolar delivery systems. Bipolar coagulation forceps have been used for many years and have superceded monopolar instruments for the performance of tubal sterilization largely because of safety advantages (1-3). Monopo-
Received May 6, 1994; revised and accepted August 26, 1994.
lar electrodes effect action at the electrode-tissue interface by the creation of high current density (power density), conversion of electrical to thermal energy, and the return of current to ground (via ground plate and electrosurgical generator) using the patient as the intermediary conductor. In contrast, bipolar electrodes are coupled such that one part serves as the active electrode and its mate serves as the neutral (return) electrode. Therefore, current passes only through the tissue held between the jaws of the forceps and not indiscriminately through the body of the patient. The risks of high frequency leakage and dangerous current splitting to ground therefore are minimized (4-6). The application of bipolar technology to effect cutting tissue by means of bipolar scissors is reported herein. This new device was compared with monopolar scissors in so far as hemostasis attained and tissue thermal artifact produced.
* Reprint requests: Michael S. Baggish, M.D., Department of Obstetrics and Gynecology, Good Samaritan Hospital, 375 Dixmyth Avenue, Cincinnati, Ohio 45220 (FAX: 513-221-5865). t Department of Pathology and Biomedical Engineering, University of Iowa. 422
Baggish and Tucker Techniques and instrumentation
MATERIALS AND METHODS
The study was carried out at three centers: Good Samaritan Hospital, Cincinnati, Ravenswood HosFertility and Sterility
pital, Chicago, and The University of Iowa. Eighteen New Zealand female rabbits weighing 5 to 6 kg were anesthetized with 5 mg/kg Rompun 5 mg/kg and 35 mg/kg Ketamine. The animals underwent laparotomy via midline incision; the uterine horns were exposed. The horn was cut into segments using bipolar scissors (left horn) and monopolar scissors (right horn). Ninety-four cuts were made at varying power settings: 25, 30, 35, 40, 45, and 50 W. Each segment was removed and pinned flat to prevent curling. The samples were fixed 24 to 48 hours in 10% buffered formalin. The samples were embedded in paraffin, sectioned, stained with hematoxylin and eosin, and evaluated microscopically. The area of thermal coagulation, i.e., irreversible injury, was measured using an Olympus-Vanox T Photomicroscope (Olympus, Lake Success, NY) with built-in stage micrometer. The units of measurement on the micrometer were calibrated at various objective powers (X4, X10, X20) against a Zeiss and Olympus 1 mm standard (Zeiss, Thornwood, NY), consisting of 100 subdivisions (0.01 mm). Zone of thermal injury (mm) was plotted against applied energy (watts) and statistically analyzed by Wilcoxon and Sign nonparametric methods. Monopolar and bipolar data were compared. Because both sets of data were completely matched, a difference curve was constructed. Specification Scissors
Bipolar scissors were supplied by Everest Medical (Minneapolis, MN). The design of the insulated dual-action scissors consists of stainless steel electrodes bonded opposite to the ceramic cutting surfaces of the two blades. The shaft diameter of the scissors was 5 mm and the working length was 33 cm or 45 cm. Monopolar scissors were supplied by Ethicon Endosurgery (Cincinnati, OH). The 5-mm diameter scissors was curved and insulated to the exposed blades with 0.008- to 0.009-inch (0.200 to 0.225 mm) Teflon. The working length measured 33 cm. The electrodes consisted of stainless steel blades (both cutting and reverse surfaces). Both pieces of equipment were disposable (single use). Specifications of Electrosurgical Generator
Two types of electro surgical generators were used for the experiment. Each is designed to deliver maximum output power into a resistive load of approximately 300 n. Erbe MCC 350 (Erbe, Tublingen, Germany) and Valleylab Force 2 (Valley LaboVol. 63, No.2, February 1995
E
.s>
0.10
a: J
0.40'
~
0.10'
.., ..J
cC
:E
0.20'
::J: l-
0.10'
a: w II.
0
(B)
0.10'
0.00'
III W
Z
0
·0.10 20
II
10
II
40
411
10
15
N APPLIED WATTS
Figure 1 Plot of zones of thermal injury associated with increasing wattage for both monopolar (e; B) and bipolar (A; A) scissors. The delta thermal injury is plotted in C (0).
ratories, Boulder, CO) generators represent two totally different technologies: The Erbe MCC 350 generator exemplifies constant voltage output, with microprocessor technology and peak voltages ranging from 200 to 600 V at the electrode-tissue interface. The generator operates at a frequency 350 kHz and is equipped with bipolar pure sign wave output (cutting current). The ValleylabForce 2 generator is not a constant voltage generator. In bipolar mode, it produces 0 to 800 V open circuit operating at 500 kHz. It is not equipped with automatic bipolar technology. Standardization of Electrosurgical Cutting Velocity
Because thermal damage relates to the duration of electric current on tissue, quantification of cutting velocity was considered important. This was attained by performing a deliberate and exaggerated motion lasting 1 second for each mechanical cutting action of the scissors. In fact, during the experiments, this method of cutting was found to produce the most effective hemostasis. RESULTS
Figure 1 details a plot of zones of damage associated with increasing wattage for both monopolar and bipolar scissors. Monopolar data is shown in curve B, bipolar data is shown in curve A, and the difference between curve B and curve A is shown in curve C. The bipolar data follows a path that closely approximates a straight line from 25 to 50 W. Significantly greater damage to tissue collated with inBaggish and Tucker Techniques and instrumentation
423
> a: :::)
... ~ IL
0
W
Z
0
N
Z C
W
::E
0.11 0.10' D.lI' 0.10' 0.411' 0.40' 0.86 0.10' O.U' 0.20' 0.11' 0.10' O.OS 0.00 20
NOTI!: • DATA
IIIII'~.D
IIY , WATT I'0Il_ C.
OONTIIAIIT IIETWEEN THE • AND 110 .-LOTII
J/././
/1
(C)
,..J.:,/"//
(A)
25
81
80
50
411
40
61
APPLIED WATTS
> a: :::)
... ~ IL
0
W
Z
2
z
C
W
::E
o.e5 0.80' 0.11' 0.10' 0.411' 0.40' 0.86' 0.80' D.25 0.20' 0.11' 0.10' O.OS 0.00 110
Memll .. DATA DI"U._ IIY , WATT 1'011 MIIII OP CONTIIAIT ..,....M .. AND . . PLOTII
I/
•
,.1
(0)
..,-/ /","
;;----'
U
80
81
40
411
50
Iii
APPLIED WATTS
Figure 2 (A), Mean zones of damage created by bipolar (&; A) and monopolar (e; B) scissors. Error bars, 95% confidence intervals. (B), The same data as in A plotted with 2 SD error bars.
creasing applied wattage when time on tissue was held constant (P < 0.001). The monopolar data also showed a strongly significant fit (P < 0.001) to a second order polynomial of increasing thermal damage with increasing wattage. The values for thermal damage at a given wattage were always larger in this curve than they were in the bipolar curve. Curve C illustrates the difference values between the two sets of above data. The equation for this difference has a strongly significant fit (P < 0.001) to a linear function that expresses how much larger the monopolar data is than the bipolar data. The equation is given by Delta = (Mo - Bi) = 1.92 X AW + 0.0001 and clearly states that on the average and at any value of AW, applied wattage, the monopolar data will be about twice as large as the bipolar data. Figure 2A plots mean areas of damage generated by the two scissor types as functions of the applied wattage and is accompanied by an error bar that encompasses the 95% confidence intervals for that mean. Figure 2B plots the same data with two stan424
Baggish and Tucker
Techniques and instrumentation
dard deviation error bars. Figure 3 illustrates the strong correlation between areas of thermal injury induced by the two methods. This plot is misleading in the sense that injury induced by one method is not dependent on injury induced by the second method. However, it clearly illustrates that the use of thermal energy, which is common to both methods, causes similar areas of damage when it is applied by either method. The area of injury caused by a given wattage in the monopolar method is two times as large as that generated by the bipolar method. Of particular interest in this plot is the lack of data seen in the midregion of the plot. Despite the fact that wattages were uniformly increased in 5 W increments, the data do not show a continuous series of points over the area range. This region is identified as the "GAP" region on the plot. Other than larger zones of thermal injury, little benefit could be observed with power settings> 35 W with either bipolar or monopolar modality. Five times less mean thermal injury was observed with the constant voltage-automatic bipolar electrosurgical unit (ESU) compared with the conventional ESU at 25 W. The area of coagulation necrosis was easily identified (Fig. 4A). The outer edge of the zone was marked by a thin line of cellular debris and/or carbonization. The "dead zone," i.e., irreversible injury, was marked by deep blue or purple staining that was in sharp contrast to the light blue uptake of the surrounding viable tissue. Cellular detail was indistinct within the zone (Fig. 4B). Nuclei were
> a:
...~ :::)
0.10
.:
0.50
..
IL
0
0.40'
W
Z
0
N
0.80
c...I
0.20'
::J
a:
0 D. 0 Z 0 :::E
..
.'
GAP
0.10 0.00 0.00
0.05
0.10
0.11
0.20
0.115
0.80
BIPOLAR ZONE OF INJURY
Figure 3 Regression of injury from monopolar versus bipolar scissors. Thermal energy results in similar areas of damage when applied by either method. The area of injury generllted by monopolar scissors at any given wattage is two times greater than that generated by bipolar scissors. b., areas of injury. Monopolar = 1.99(bipolar); n = 30; r = 0.9741.
Fertility and Sterility
pyknotic and bizarrely elongated or smudged. Within the zone and neighboring the zone, blood vessels and lymphatics were thrombosed or collapsed (Fig. 4C). Occasionally vacuoles were created and sometimes filled with proteinaceous fluid. The latter were associated with the more extensive destruction, i.e., >200 JLm (Fig. 4D). Cut modes of the ESU produced sinusoidal outputs. However, the amplitude variations and high frequency components ofthe Valleylab system contrasted to the purely sinusoidal constant voltage output of the Erbe ESU. The Erbe ESU with a frequency of 350 kHz generated more or less pure sinusoidal shape waveforms that were independent of the resistive load or power setting. The Valleylab ESU with a fundamental frequency of 500 kHz produced a waveform that was asymmetric and noisy with several harmonics. DISCUSSION
Several problems are associated with the use of monopolar devices during operative laparoscopy. These include direct coupling, capacitive coupling, and high frequency leakage (4, 5). In an effort to diminish these inherent risks, gynecologists have in the past turned to bipolar technology (6). Until recently, no bipolar cutting devices were available for use during laparoscopic surgery. The bipolar scissors used in this investigation proved to be at least equally efficacious when compared with their monopolar counterparts. With either of the two generators used in this experiment, the areas of thermal artifact were less with bipolar than monopolar scissors. Hemostasis was adequate with both pairs of scissors tested. Because the bipolar technology is not associated with capacitive or direct coupling, they are safer to use with laparoscopic techniques, particularly in situations where peripheral vision is diminished. Although thermal injury can occur with bipolar instruments, those injuries relate to the surgeon picking up the wrong
Figure 4 (A), Section of rabbit horn (X40) showing thin line of carbon formation. Bipolar cut, 30 W. (B), Magnification (X100) showing 0.1 mm necrotic zone (arrows) characterized by deeper staining, distorted nuclei, and cells. The line of carbonization can be seen at the 65 division mark of the micrometer. Bipolar cut, 30 W. (C), Thermal damage measuring 0.34 mm after a 30 W monopolar cut (X40). (D), Magnification (X200) of Figure 3 showing thrombosed vessels (white arrows), elongated bizarre nuclei, and vacuoles containing proteinaceous material (dark arrows). These changes were seen with thermal injury zones> 200 11m. Monopolar cut, 30 W. Vol. 63, No.2, February 1995
Baggish and Tucker
Techniques and instrumentation
425
structure or by conductive spread of heat associated with prolonged time of application. Obviously, the same additional difficulties can happen additively with monopolar instruments as well. Effective cutting of tissue occurs with voltages between 200 and 600. Carbonization and excessive coagulation are reduced when electrode-tissue interface operates at voltages < 600. Unfortunately, conventional generators cannot produce voltages < 600 unless the power is set very low «20 W) creating very slow cutting. Constant voltage generators maintain this preferable peak to peak voltage at <600 V even at high powers, therefore, thermal injury (coagulation necrosis) zones are decreased. When high frequency current flows through constrictions in tissue using monopolar techniques, the thermal action starts at the point of constriction and not at the point where the electrode touches the tissue (decreased area increases current density and thus thermal damage). Thus, the initial flow of current may be outside the field of the operator's view. With bipolar application, the site ofthe thermal action is at the position of electrodes. Coagulation occurs at 70°C whereupon collagens within the clot are converted into glucose, producing an adhesive effect, causing the clot to stick to the electrode. When sticking occurs, the blood vessel and clot are avulsed, reopening the blood vessel, as the electrode is pulled away. Automatic bipolar control based on the change in electrical resistance of the coagulated tissue relative to the temperature of the tissue helps to ensure that the electrode remains clean during cutting and coagulation. Addi-
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tionally, unnecessary long and intensive coagulation increases the risk of accidental burns by conduction. Based on this study one could conclude that bipolar scissors perform competitively with monopolar scissors relative to hemostasis, speed, and secondary thermal injury. Bipolar scissors offer the surgeon and the patient significant safety advantages, particularly when coupled to a microprocessor controlled electrosurgical generator. Acknowledgment. The authors thank Robert Johnson, Ph.D., of the Good Samaritan Hospital Research Department, Cincinnati' Ohio, for performing the statistical tests.
REFERENCES 1. Thompson BN, Wheeless CR. Gastrointestinal complications of laparoscopic sterilization. Obstet Gynecol 1973; 41:669-74. 2. Tucker RD, Benda JA, Sievert CE, Engel T. The effect of bipolar electrosurgical coagulation waveform on a rat uterine model of fallopian tube sterilization. J Gynecol Surg 1992;8:235-41. 3. Tucker RD, Benda JA, Mardan A, Engel T. The interaction of electrosurgical bipolar forceps and generators on an animal model of fallopian tube sterilization. Am J Obstet Gynecol 1991;165:443-9. 4. Baggish MS, Diamond MP, Nezhat C, Rock JA, SanFilippo JS. Overcoming complications of laparoscopic surgery I. Contemp Ob Gyn 1994;39:92-106. 5. Voyles CR, Tucker RD. Education and engineering solutions for potential problems with laparoscopic monopolar electrosurgery. Am J Surg 1992;164:57-62. 6. Baggish MS. Is it necessary to repeat history [editorial]? J Gynecol Surg 1989;5:323.
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