CA2280313A1 - Dispersive electrode skin burns during electrosurgery - Google Patents
Dispersive electrode skin burns during electrosurgery Download PDFInfo
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- CA2280313A1 CA2280313A1 CA 2280313 CA2280313A CA2280313A1 CA 2280313 A1 CA2280313 A1 CA 2280313A1 CA 2280313 CA2280313 CA 2280313 CA 2280313 A CA2280313 A CA 2280313A CA 2280313 A1 CA2280313 A1 CA 2280313A1
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- 231100000075 skin burn Toxicity 0.000 title claims abstract description 11
- 230000004913 activation Effects 0.000 claims abstract description 10
- 230000002035 prolonged effect Effects 0.000 claims abstract description 5
- 238000000034 method Methods 0.000 claims description 14
- 208000027418 Wounds and injury Diseases 0.000 abstract description 11
- 230000006378 damage Effects 0.000 abstract description 11
- 208000014674 injury Diseases 0.000 abstract description 11
- 230000003902 lesion Effects 0.000 abstract description 7
- 238000005516 engineering process Methods 0.000 abstract description 5
- 238000001356 surgical procedure Methods 0.000 abstract description 5
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 abstract description 4
- 239000011780 sodium chloride Substances 0.000 abstract description 4
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- 238000012544 monitoring process Methods 0.000 abstract description 2
- 230000000630 rising effect Effects 0.000 abstract description 2
- 210000001519 tissue Anatomy 0.000 description 14
- 238000002679 ablation Methods 0.000 description 4
- 210000000689 upper leg Anatomy 0.000 description 4
- 201000010260 leiomyoma Diseases 0.000 description 3
- DHMQDGOQFOQNFH-UHFFFAOYSA-N Glycine Chemical compound NCC(O)=O DHMQDGOQFOQNFH-UHFFFAOYSA-N 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 230000002262 irrigation Effects 0.000 description 2
- 238000003973 irrigation Methods 0.000 description 2
- 238000011471 prostatectomy Methods 0.000 description 2
- 239000000523 sample Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 230000008016 vaporization Effects 0.000 description 2
- 238000009834 vaporization Methods 0.000 description 2
- 206010061692 Benign muscle neoplasm Diseases 0.000 description 1
- 206010006803 Burns third degree Diseases 0.000 description 1
- FBPFZTCFMRRESA-FSIIMWSLSA-N D-Glucitol Natural products OC[C@H](O)[C@H](O)[C@@H](O)[C@H](O)CO FBPFZTCFMRRESA-FSIIMWSLSA-N 0.000 description 1
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical compound OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 description 1
- 206010013786 Dry skin Diseases 0.000 description 1
- 239000004471 Glycine Substances 0.000 description 1
- 201000004458 Myoma Diseases 0.000 description 1
- 206010040914 Skin reaction Diseases 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000008280 blood Substances 0.000 description 1
- 210000004369 blood Anatomy 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 210000000170 cell membrane Anatomy 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 230000001186 cumulative effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 229940079593 drug Drugs 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000037336 dry skin Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 230000002357 endometrial effect Effects 0.000 description 1
- 210000000981 epithelium Anatomy 0.000 description 1
- 230000003090 exacerbative effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
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- 238000012806 monitoring device Methods 0.000 description 1
- 210000003205 muscle Anatomy 0.000 description 1
- 230000017074 necrotic cell death Effects 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 230000001850 reproductive effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 230000035483 skin reaction Effects 0.000 description 1
- 231100000430 skin reaction Toxicity 0.000 description 1
- 239000000600 sorbitol Substances 0.000 description 1
- 239000006200 vaporizer Substances 0.000 description 1
Classifications
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
- A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
- A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
- A61B18/14—Probes or electrodes therefor
- A61B18/16—Indifferent or passive electrodes for grounding
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
- A61B2018/00636—Sensing and controlling the application of energy
- A61B2018/00642—Sensing and controlling the application of energy with feedback, i.e. closed loop control
- A61B2018/00654—Sensing and controlling the application of energy with feedback, i.e. closed loop control with individual control of each of a plurality of energy emitting elements
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
- A61B2018/00636—Sensing and controlling the application of energy
- A61B2018/00773—Sensed parameters
- A61B2018/00791—Temperature
- A61B2018/00797—Temperature measured by multiple temperature sensors
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- Health & Medical Sciences (AREA)
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- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
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- Otolaryngology (AREA)
- Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
- Plasma & Fusion (AREA)
- Physics & Mathematics (AREA)
- Heart & Thoracic Surgery (AREA)
- Medical Informatics (AREA)
- Molecular Biology (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Surgical Instruments (AREA)
Abstract
This invention relates to skin burns at the return electrode site (dispersive electrode, pad electrode, ground pad) that have been experienced during transurethral prostactectomy, Hysteroscopic surgery and other types of electrosurgery even when dispersive electrodes with a Return Electrode Monitoring (REM) system are used. The mechanisms of burn is temperature rising over 45°C at the electrode/skin interface due to excessive current density exceeding the dispersive capacity of pad electrode. In particular this invention is to develop dispersive electrodes with temperatures sensors and alarms, similar to the REM system, warning with flashing lights and/or sound and deactivating the electrical generator (ESU) when the temperature at the electrode/tissue interface rises above 45°C. To avoid or minimize the risks of such an injury the surgeon should consider the following: use the minimum effective power output to vaporize the intended tissue; avoid prolonged activation intervals of the ESU and allow sufficient time between activation periods to dissipate the heat built up at the dispersive electrode/skin interface; consider dispersive electrodes with larger surface area; consider dispersive electrodes with temperature sensors and alarms, similar to the REM system, deactivating the ESU when temperature rises to inappropriate levels; and/or consider bipolar electrosurgical technology, such as coaxial bipolar electrodes (Versapoint TM) that cut, desiccate and vaporize intrauterine lesions in a saline environment.
Description
DISPERSIVE ELECTRODE SKIN BURNS DURING ELECTROSURGERY
FIELD OF THE INVENTION
This invention relates to methods and apparatus to avoid dispersive electrode skin burns during electrosurgery.
BACKGROUND OF THE INVENTION
A Case History A 40-year-old African American patient had a 3-cm submucous leiomyoma vaporized hysteroscopically on November 4, 1996 with the VaporTrodeTM grooved electrode (Circon ACMI, Stamford, Connecticut) and a Valleylab Force 2 electrosurgical generator (ESU, Valleylab, Boulder CO) as described in Brooks PG. (Resectoscopic myoma vaporizer. J
Reproductive Medicine 1995; 40; 791-795) and Glasser MH, (Endometrial ablation and hysteroscopic myomectomy by electrosurgical vaporization.
J Am Assoc Gynecol Laparose 1997; 4; 369-374). The current in the cut mode was increased step-wise from 180 to 300 watts until adequate vaporization of the fibroid was achieved. No alarms, flashing lights, bells or whistles were raised during the procedure which lasted approximately 20 minutes of generator activation time. Following removal of the dispersive electrode from the patient's left thigh "deep second-to-third-degree burns on the medial and superolateral aspect of the margin where the cautery pad was applied" were noted. The lesion required skin grafting and healed accordingly.
This report by Dr. Raders is the first one in the literature describing a dispersive electrode, with a REM system, skin burn during gynaecological resectoscopic surgery. An incident in which a 65-year-old patient's thigh was burned at the return electrode site during transurethral prostatectomy (TURP) has been reported in ECRI, Health Devices, Hazard Report: Skin Burns Resulting from the Use of Electrolytic Distension/Irrigation Media during Electrosurgery with Roller Ablation Electrode, June 1998, Vol. 27 No. 6, pages 233-235.
Valleylab Report The engineering group at the Valleylab performed an analysis of the potential cause of this patient's injury. During simulation of the procedure, the maximum current measured was 440 mA (rounded to 500 mA). Since a Valleylab REM patient return electrode has a surface area of 126 cm2 the maximum current density through the dispersive electrode would have been 500 mA divided by 126 cm2 or approximately 4 mA/cm2. It has been published by Becker et al. that a current density in excess of 50 mA/cm2 was required to cause reddening of a volunteers' skin as described in Becker CM, Malhotra IV, Hedley-Whyte J. The distribution of radio frequency current burns. Anesthesiology, 1973; 38 (2):106-121.
In addition the engineers calculated the heatng factor (HF) of the dispersive electrode defined as the current2 x the duration of the current (HF=I2t) expressed in Amperes2seconds (A2s) and reported that "both the heating factor and current density calculations led engineering to believe that the reported lesion was not of thermal origin. The true cause of this lesion may never be known. Pressure necrosis is often mistaken for an electrosurgical injury, as well as skin reaction to materials."
ECRI Report The entire system used in this case was systematically and thoroughly evaluated by Emergency Care Research Institute (ECRI, Plymouth, PA). They reported that "there were no electrical breaks anywhere along the system and all components functioned as they were supposed to do with no alarms raised during the procedure."
To elucidate the possible mechanism of such an injury one must follow the electrical current from the ESU to the VaporTrode electrode and its return through the dispersive electrode back to the generator. The ECRI report on the three components of the electrical system was as follows:
FIELD OF THE INVENTION
This invention relates to methods and apparatus to avoid dispersive electrode skin burns during electrosurgery.
BACKGROUND OF THE INVENTION
A Case History A 40-year-old African American patient had a 3-cm submucous leiomyoma vaporized hysteroscopically on November 4, 1996 with the VaporTrodeTM grooved electrode (Circon ACMI, Stamford, Connecticut) and a Valleylab Force 2 electrosurgical generator (ESU, Valleylab, Boulder CO) as described in Brooks PG. (Resectoscopic myoma vaporizer. J
Reproductive Medicine 1995; 40; 791-795) and Glasser MH, (Endometrial ablation and hysteroscopic myomectomy by electrosurgical vaporization.
J Am Assoc Gynecol Laparose 1997; 4; 369-374). The current in the cut mode was increased step-wise from 180 to 300 watts until adequate vaporization of the fibroid was achieved. No alarms, flashing lights, bells or whistles were raised during the procedure which lasted approximately 20 minutes of generator activation time. Following removal of the dispersive electrode from the patient's left thigh "deep second-to-third-degree burns on the medial and superolateral aspect of the margin where the cautery pad was applied" were noted. The lesion required skin grafting and healed accordingly.
This report by Dr. Raders is the first one in the literature describing a dispersive electrode, with a REM system, skin burn during gynaecological resectoscopic surgery. An incident in which a 65-year-old patient's thigh was burned at the return electrode site during transurethral prostatectomy (TURP) has been reported in ECRI, Health Devices, Hazard Report: Skin Burns Resulting from the Use of Electrolytic Distension/Irrigation Media during Electrosurgery with Roller Ablation Electrode, June 1998, Vol. 27 No. 6, pages 233-235.
Valleylab Report The engineering group at the Valleylab performed an analysis of the potential cause of this patient's injury. During simulation of the procedure, the maximum current measured was 440 mA (rounded to 500 mA). Since a Valleylab REM patient return electrode has a surface area of 126 cm2 the maximum current density through the dispersive electrode would have been 500 mA divided by 126 cm2 or approximately 4 mA/cm2. It has been published by Becker et al. that a current density in excess of 50 mA/cm2 was required to cause reddening of a volunteers' skin as described in Becker CM, Malhotra IV, Hedley-Whyte J. The distribution of radio frequency current burns. Anesthesiology, 1973; 38 (2):106-121.
In addition the engineers calculated the heatng factor (HF) of the dispersive electrode defined as the current2 x the duration of the current (HF=I2t) expressed in Amperes2seconds (A2s) and reported that "both the heating factor and current density calculations led engineering to believe that the reported lesion was not of thermal origin. The true cause of this lesion may never be known. Pressure necrosis is often mistaken for an electrosurgical injury, as well as skin reaction to materials."
ECRI Report The entire system used in this case was systematically and thoroughly evaluated by Emergency Care Research Institute (ECRI, Plymouth, PA). They reported that "there were no electrical breaks anywhere along the system and all components functioned as they were supposed to do with no alarms raised during the procedure."
To elucidate the possible mechanism of such an injury one must follow the electrical current from the ESU to the VaporTrode electrode and its return through the dispersive electrode back to the generator. The ECRI report on the three components of the electrical system was as follows:
1. The Vaportrode Electrode "There was nothing from inspection or testing to suggest the electrode contributed to the incident."
2. The Dispersive Electrode (REM type,126 cm2) "The pad was unremarkable with the exception of a black skin tissue fragment (5 x 12 mm in size) stuck on the long side of the pad that has the tab extension where the cable is attached.
There were no signs of electrical arcs or overheating in the area of the conductive gel."
3. The Valleylab Force 2 ESU
"All ECRI tests revealed that the generator performed within the manufacturer's specifications and that all alarms were operational. However, this does not preclude the possibility that the unit contributed to the injury since there are significant differences in performance between the Force 2 and other models and makes of ESU's in the current delivering capability into output load impedances."
SUMMARY OF THE INVENTION
Skin burns at the return electrode site (dispersive electrode, pad electrode, ground pad) have been experienced during transurethral prostactectomy, Hysteroscopic surgery and other types of electrosurgery even when dispersive electrodes with a Return Electrode Monitoring (REM) system are used. The mechanisms of burn is temperature rising over 45°C at the electrode/skin interface due to excessive current density exceeding the dispersive capacity of pad electrode.
Proposed Solution to Avoid Injury Develop dispersive electrodes with temperatures sensors and alarms, similar to the REM system, warning with flashing lights and/or sound and deactivating the electrical generator (ESU) when the temperature at the electrode/tissue interface rises above 45°C. One might couple the REM and Temperature Monitoring Device into one system.
For example, to avoid or minimize the risks of such an injury the surgeon should consider the following:
1. Use the minimum effective power output to vaporize the intended tissue;
2. Avoid prolonged activation intervals of the ESU and allow sufficient time between activation periods to dissipate the heat built up at the dispersive electrode/skin interface;
3. Consider dispersive electrodes with larger surface area;
4. Consider dispersive electrodes with temperature sensors and alarms, similar to the REM system, deactivating the ESU when temperature rises to inappropriate levels; and/or 5. Consider bipolar electrosurgical technology, such as coaxial bipolar electrodes (VersapointTM ) that cut, desiccate and vaporize intrauterine lesions in a saline environment.
DESCRIPTION OF THE INVENTION
Basic Electrosurgery The flow of current in Amperes is directly proportional to the driving force (voltage) in Volts and inversely proportional to the resistance offered by the conductor in Ohms (Ohms law: I=V/R).
Biological tissue has its own minute electricity (in mV) and a component of capacitance as a result of the cell membranes maintaining unequal distribution of ions across them. Therefore the resistance offered by biological tissue is referred to as impedance rather than resistance and it is also expressed in Ohms. The impedance measured in various biological tissues has been approximated to be 30 Ohms for blood, 300-400 Ohms for muscle, 1,000-2,000 Ohms for fat, 1,000 Ohms for wet epithelium and over 100,000 Ohms for dry skin.
The load impedance that the patient circuit presents to the ESU
determines the current that passes through the system and subsequently through the dispersive electrode. The load impedance is the sum of the impedances of the active electrode tissue interface, plus the impedance through the patient's body between the active site and the dispersive electrode plus the dispersive electrode in contact with skin interface.
5 According to ERCI "a low value of load impedance in combination with the use of a Valleylab Force 2 ESU will result in higher currents through the dispersive electrode than will result with most other ESU's. The Force 2 delivers substantially higher output current when the total connected circuit impedance is lower than 150 Ohms."
The VaporTrode electrode is a 3-mm in width grooved rollercylinder which offers a greater-than-usual contact area with the tissue than the cutting loop or the rollerball. Therefore according to the ECRI, conditions were present n the incident surgery that predisposed toward low total-load impedance with resulting higher-than-usual expected currents born by the dispersive electrode. Contributors to those conditions included: an electrode with a greater-than-usual contact area with the leiomyoma tissues (3-mm in width); a high-power-demanding procedure (up to 300 watts of pure cutting current) and an ESU
delivering higher-than-usual current when low impedances are encountered.
Experimental Evidence 1. ECRI measurements suggested that when the low impedance was decreased to 100 and 50 Ohms, the Force 2 ESU delivered at a maximum power output (300 watts) was approximately 1.8 and 2.4 Amperes, respectively. Under these conditions the current density at the dispersive electrode would be approximately 14 to 19 mA/cm2 (1800 and 2400 Am = 126 cm2.
2. Heat sensing cameras over dispersive electrodes have measured temperature increases by 3 to 4°C during routine electrosurgical procedures. Temperature rise by 8 to 10°C result in skin burns at the site of the return pad electrodes. Temperature changes on the REM electrode during VaporTrode resectoscopic surgery have not been reported.
3. Limited study on a human volunteer by ECRI.
To simulate the clinical setting of the above injury a VaporTrode electrode was applied to surrogate tissue in a beaker filled with saline, glycine or sorbitol. A large metallic electrode in the beaker was connected to two Valleylab dispersive electrodes placed on a volunteer's left thigh.
To complete the circuit a single dispersive electrode was attached to the volunteers right thigh and was connected to the ESU. In addition a temperature probe was placed under the margin of the single dispersive return electrode.
The ESU was activated at a power setting of 150 watts in the cut mode with an activation cycle of 20 seconds on, 10 second off while simulated tissue ablation was performed with the rollerbar in the surrogate tissue.
After 2.5 minutes the volunteer reported noticeable heating under the single pad and the temperature probe showed a continuous rise up to 6°C that did not stabilize in that interval. The measured current through the system was approximately 1.4 A. The experiment was not repeated at higher settings or over longer periods of time for fear of causing skin burns over the volunteer's skin in contact with the dispersive single electrode in ECRI, Health Devices, Hazard Report: Skin Burns Resulting from the Use of Electrolytic Distension/Irrigation Media during Electrosurgery with Roller Ablation Electrode. June 1998, Vol. 27 No. 6, pages 233-235.
Conclusions ERCI concluded that the energy under the dispersive electrode exceeded the capacity of the pad and the underlying skin to limit the temperature rise and resulting in the lesions that were observed in the incident case.
It has been well established in the literature that current density and concomitant temperature rise are greater at the edges of a dispersive electrode than in the central conductive area. Also, the current density at the edge tends to be higher along that edge that faces the ESU site. The injuries in the incident case tend to correlate with this concept.
Recommendations This incident illuminates an area of previously unrecognized risk of electrosurgery. The exacerbating factors for such an injury are the need to vaporize large volumes of tissue (such as leiomas) requiring a larger surface contact electrode (VaporTrode) which has a larger contact impedance. In addition the procedure requires prolonged cumulative radio-frequency activity and a high power output (up to 300 watts).
To avoid or minimize the risks of such an injury the surgeon should consider the following:
1. Use the minimum effective power output to vaporize the intended tissue.
2. Avoid prolonged activation intervals of the ESU and allow sufficient time between activation periods to dissipate the heat built up at the dispersive electrode/skin interface.
3. Consider dispersive electrodes with larger surface area.
According to Tucker et al. electrosurgical return electrodes have an area of approximately 120cm2; this return electrode area has a safety margin of approximately a factor of 3. The area was chosen to dissipate the energy required for transurethral prostatectomy which is up to 300 watts.
Therefore power densities of 7.5 watts per cm2 (300 watts = 40cm2) have the potential to burn as described in Tucker R.D., Voyles R.C., Silvis S.E.
Capacitive coupled stray current during laparoscopic and endoscopic electrosurgical procedures. Biomedical Instrumentation and Technology 1992; 26: 303-311.
4. Consider dispersive electrodes with temperature sensors and alarms, similar to the REM system, deactivating the ESU when temperature rises to inappropriate levels. Such dispersive pads are not presently available.
2. The Dispersive Electrode (REM type,126 cm2) "The pad was unremarkable with the exception of a black skin tissue fragment (5 x 12 mm in size) stuck on the long side of the pad that has the tab extension where the cable is attached.
There were no signs of electrical arcs or overheating in the area of the conductive gel."
3. The Valleylab Force 2 ESU
"All ECRI tests revealed that the generator performed within the manufacturer's specifications and that all alarms were operational. However, this does not preclude the possibility that the unit contributed to the injury since there are significant differences in performance between the Force 2 and other models and makes of ESU's in the current delivering capability into output load impedances."
SUMMARY OF THE INVENTION
Skin burns at the return electrode site (dispersive electrode, pad electrode, ground pad) have been experienced during transurethral prostactectomy, Hysteroscopic surgery and other types of electrosurgery even when dispersive electrodes with a Return Electrode Monitoring (REM) system are used. The mechanisms of burn is temperature rising over 45°C at the electrode/skin interface due to excessive current density exceeding the dispersive capacity of pad electrode.
Proposed Solution to Avoid Injury Develop dispersive electrodes with temperatures sensors and alarms, similar to the REM system, warning with flashing lights and/or sound and deactivating the electrical generator (ESU) when the temperature at the electrode/tissue interface rises above 45°C. One might couple the REM and Temperature Monitoring Device into one system.
For example, to avoid or minimize the risks of such an injury the surgeon should consider the following:
1. Use the minimum effective power output to vaporize the intended tissue;
2. Avoid prolonged activation intervals of the ESU and allow sufficient time between activation periods to dissipate the heat built up at the dispersive electrode/skin interface;
3. Consider dispersive electrodes with larger surface area;
4. Consider dispersive electrodes with temperature sensors and alarms, similar to the REM system, deactivating the ESU when temperature rises to inappropriate levels; and/or 5. Consider bipolar electrosurgical technology, such as coaxial bipolar electrodes (VersapointTM ) that cut, desiccate and vaporize intrauterine lesions in a saline environment.
DESCRIPTION OF THE INVENTION
Basic Electrosurgery The flow of current in Amperes is directly proportional to the driving force (voltage) in Volts and inversely proportional to the resistance offered by the conductor in Ohms (Ohms law: I=V/R).
Biological tissue has its own minute electricity (in mV) and a component of capacitance as a result of the cell membranes maintaining unequal distribution of ions across them. Therefore the resistance offered by biological tissue is referred to as impedance rather than resistance and it is also expressed in Ohms. The impedance measured in various biological tissues has been approximated to be 30 Ohms for blood, 300-400 Ohms for muscle, 1,000-2,000 Ohms for fat, 1,000 Ohms for wet epithelium and over 100,000 Ohms for dry skin.
The load impedance that the patient circuit presents to the ESU
determines the current that passes through the system and subsequently through the dispersive electrode. The load impedance is the sum of the impedances of the active electrode tissue interface, plus the impedance through the patient's body between the active site and the dispersive electrode plus the dispersive electrode in contact with skin interface.
5 According to ERCI "a low value of load impedance in combination with the use of a Valleylab Force 2 ESU will result in higher currents through the dispersive electrode than will result with most other ESU's. The Force 2 delivers substantially higher output current when the total connected circuit impedance is lower than 150 Ohms."
The VaporTrode electrode is a 3-mm in width grooved rollercylinder which offers a greater-than-usual contact area with the tissue than the cutting loop or the rollerball. Therefore according to the ECRI, conditions were present n the incident surgery that predisposed toward low total-load impedance with resulting higher-than-usual expected currents born by the dispersive electrode. Contributors to those conditions included: an electrode with a greater-than-usual contact area with the leiomyoma tissues (3-mm in width); a high-power-demanding procedure (up to 300 watts of pure cutting current) and an ESU
delivering higher-than-usual current when low impedances are encountered.
Experimental Evidence 1. ECRI measurements suggested that when the low impedance was decreased to 100 and 50 Ohms, the Force 2 ESU delivered at a maximum power output (300 watts) was approximately 1.8 and 2.4 Amperes, respectively. Under these conditions the current density at the dispersive electrode would be approximately 14 to 19 mA/cm2 (1800 and 2400 Am = 126 cm2.
2. Heat sensing cameras over dispersive electrodes have measured temperature increases by 3 to 4°C during routine electrosurgical procedures. Temperature rise by 8 to 10°C result in skin burns at the site of the return pad electrodes. Temperature changes on the REM electrode during VaporTrode resectoscopic surgery have not been reported.
3. Limited study on a human volunteer by ECRI.
To simulate the clinical setting of the above injury a VaporTrode electrode was applied to surrogate tissue in a beaker filled with saline, glycine or sorbitol. A large metallic electrode in the beaker was connected to two Valleylab dispersive electrodes placed on a volunteer's left thigh.
To complete the circuit a single dispersive electrode was attached to the volunteers right thigh and was connected to the ESU. In addition a temperature probe was placed under the margin of the single dispersive return electrode.
The ESU was activated at a power setting of 150 watts in the cut mode with an activation cycle of 20 seconds on, 10 second off while simulated tissue ablation was performed with the rollerbar in the surrogate tissue.
After 2.5 minutes the volunteer reported noticeable heating under the single pad and the temperature probe showed a continuous rise up to 6°C that did not stabilize in that interval. The measured current through the system was approximately 1.4 A. The experiment was not repeated at higher settings or over longer periods of time for fear of causing skin burns over the volunteer's skin in contact with the dispersive single electrode in ECRI, Health Devices, Hazard Report: Skin Burns Resulting from the Use of Electrolytic Distension/Irrigation Media during Electrosurgery with Roller Ablation Electrode. June 1998, Vol. 27 No. 6, pages 233-235.
Conclusions ERCI concluded that the energy under the dispersive electrode exceeded the capacity of the pad and the underlying skin to limit the temperature rise and resulting in the lesions that were observed in the incident case.
It has been well established in the literature that current density and concomitant temperature rise are greater at the edges of a dispersive electrode than in the central conductive area. Also, the current density at the edge tends to be higher along that edge that faces the ESU site. The injuries in the incident case tend to correlate with this concept.
Recommendations This incident illuminates an area of previously unrecognized risk of electrosurgery. The exacerbating factors for such an injury are the need to vaporize large volumes of tissue (such as leiomas) requiring a larger surface contact electrode (VaporTrode) which has a larger contact impedance. In addition the procedure requires prolonged cumulative radio-frequency activity and a high power output (up to 300 watts).
To avoid or minimize the risks of such an injury the surgeon should consider the following:
1. Use the minimum effective power output to vaporize the intended tissue.
2. Avoid prolonged activation intervals of the ESU and allow sufficient time between activation periods to dissipate the heat built up at the dispersive electrode/skin interface.
3. Consider dispersive electrodes with larger surface area.
According to Tucker et al. electrosurgical return electrodes have an area of approximately 120cm2; this return electrode area has a safety margin of approximately a factor of 3. The area was chosen to dissipate the energy required for transurethral prostatectomy which is up to 300 watts.
Therefore power densities of 7.5 watts per cm2 (300 watts = 40cm2) have the potential to burn as described in Tucker R.D., Voyles R.C., Silvis S.E.
Capacitive coupled stray current during laparoscopic and endoscopic electrosurgical procedures. Biomedical Instrumentation and Technology 1992; 26: 303-311.
4. Consider dispersive electrodes with temperature sensors and alarms, similar to the REM system, deactivating the ESU when temperature rises to inappropriate levels. Such dispersive pads are not presently available.
5. Consider bipolar electrosurgical technology which eliminates the need for dispersive electrodes. Coaxial bipolar electrodes (VersapointTM) that cut, desiccate and vaporize intrauterine lesions in a saline environment are now available (Versapoint, Gynecare, Menlo Park, CA) in Tucker R.D., Voyles R.C., Silvis S.E. Capacitive coupled stray current during laparoscopic and endoscopic electrosurgical procedures.
Biomedical Instrumentation and Technology 1992; 26: 303-311.
Biomedical Instrumentation and Technology 1992; 26: 303-311.
Claims (5)
1. A method of minimizing or avoiding dispersive electrode skin burns during electrosurgery comprising the following:
a) using minimum effective power output to vaporize the intended tissue; and/or b) avoiding prolonged activation intervals of the ESU and allowing sufficient time between activation periods to dissipate heat build up at the dispersive eleectrode.
a) using minimum effective power output to vaporize the intended tissue; and/or b) avoiding prolonged activation intervals of the ESU and allowing sufficient time between activation periods to dissipate heat build up at the dispersive eleectrode.
2. A method according to claim 1 wherein said electrosurgery is carried out using dispersive electrodes.
3. A method according to claim 2 wherein said dispersive electrodes are selected having large surface area
4. A method according to claim 2 wherein said dispersive electrodes comprise temperature sensors and alarms.
5. A method according to claim 1 wherein said electrosurgery is carried out using coaxial bipolar electrodes.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2280313 CA2280313A1 (en) | 1999-08-17 | 1999-08-17 | Dispersive electrode skin burns during electrosurgery |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2280313 CA2280313A1 (en) | 1999-08-17 | 1999-08-17 | Dispersive electrode skin burns during electrosurgery |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2280313A1 true CA2280313A1 (en) | 2001-02-17 |
Family
ID=4163975
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2280313 Abandoned CA2280313A1 (en) | 1999-08-17 | 1999-08-17 | Dispersive electrode skin burns during electrosurgery |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2280313A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8118807B2 (en) | 2004-04-16 | 2012-02-21 | Sydney West Area Health Service | Biomedical return electrode having thermochromic layer |
-
1999
- 1999-08-17 CA CA 2280313 patent/CA2280313A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8118807B2 (en) | 2004-04-16 | 2012-02-21 | Sydney West Area Health Service | Biomedical return electrode having thermochromic layer |
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