- Email: [email protected]
Electrosurgery 101
TECHNOLOGY
Electrosurgery 101 Charles W. Van Way III, MD Department of Medical Education, St. Luke’s Hospital, Kansas City, Missouri INTRODUCTION: THE UNEXPLORED COUNTRY Electrosurgical technology is a basic part of operative surgery. Few surgeons will operate without using it. And yet, basic principles and practical applications of electrosurgery are poorly understood. Unhappily, most surgeons minimize the importance of electrosurgery. We don’t understand it, and we don’t particularly think we need to understand it. We just use it. More particularly, residents are not given formal instruction in its use. Operating room personnel are usually trained by the manufacturer’s representatives. Most surgeons rely on operating room nursing personnel when setting up electrosurgical equipment. That is to say, we rely on people trained by sales representatives. Actually, the sales representatives are responsible individuals and well trained on the equipment. It would be nice if surgical residents knew as much as the average representative. Now, operating room personnel do their best. But even people doing their best can make mistakes. Injuries resulting from electrosurgery are the most common reason for malpractice suits against hospitals, resulting from operations. OK, so we don’t know enough. But, what should we know? On the theoretical side, it would be good to understand the difference between cutting and coagulation current, as well as the characteristics of radio-frequency current used in electrosurgery. On the practical side, it is important to know about the differing varieties, such as fulguration and desiccation, to be able to tell operating room personnel how to adjust the equipment, to identify common hazards, and to know how to prevent injuries. Electrosurgical technology is neither self-evident nor inherently safe. Injuries resulting from electrosurgery may be catastrophic. As an extreme example, some years ago, a patient being operated on in a large West Coast teaching hospital caught on fire and died. Electrosurgery was being used at the time. The professor and the resident didn’t have a clue as to what happened. The fire was probably caused by arcing at the dispersive electrode—the “ground pad”— or it may have been
Correspondence: Inquiries to Charles W. Van Way III, MD, Dept. of Medical Education, St. Luke’s Hospital, 4401 Wornall Road, Kansas City, MO 64111; fax: (816) 932-5179; e-mail: [email protected]
172
caused by equipment failure. Both the surgeons and the hospital were successfully sued. This paper is intended to be the first of a series, whose purpose will be to provide the background and the basics of electrosurgery. The first installment will discuss basic electrosurgical coagulation and cutting, and have a few words about safety. Subsequent papers will discuss electrosurgical physics, the use of electrosurgery in laparoscopic surgery, and new technologies. Several new technologies exist, including the argon beam coagulator, Faraday shield technology to prevent injury during laparoscopy, and radio-frequency destruction of tissue in cardiology and surgical oncology.
WHAT’S IN A NAME? The proper name of the technology is electrosurgery. The term “electrocautery” is often used. Actually, electrocautery refers to the use of electricity to heat an iron to be used as a hot cautery. One might compare it to a surgical soldering iron. Electrosurgery is most commonly monopolar, in which a single electrode is used, and the return circuit is through a dispersive pad (ground pad, to most of us). Monopolar electrosurgery can produce both coagulation and cutting. Bipolar electrosurgery uses a type of forceps in which the current passes between the arms of the forceps. It is used widely in neurosurgery. Bipolar electrosurgery is limited to coagulation mode. Other names are used to describe the modes of electrosurgery, which depend to some extent on the type of current used. Electrodissection is use of electrosurgery to divide tissue; i.e., cutting. Electrocoagulation is electrosurgery in its coagulation mode, used for hemostasis. Two major types of electrocoagulation, fulguration and desiccation, exist. Both types refer to coagulation of tissue produced by monopolar electrosurgery. In desiccation, the electrode is held in contact with the tissue or with a clamp to produce a zone of coagulation by direct contact. In fulguration, the electrode is held slightly above the tissue, so that the current travels across a gap to reach the tissue. The current actually travels through air by ionizing the nitrogen, creating a current path from the electrode to the tissue. The ionized current path lasts for only a few milliseconds, so that the appearance of an electrode during fulguration shows multiple ionization pathways. It looks like multiple miniature lightening strikes: (Fig. 1). Two types of current are used in electrosurgery: cutting cur-
CURRENT SURGERY • © 2000 by the Association of Program Directors in Surgery Published by Elsevier Science Inc.
0149-7944/00/$20.00 PII S0149-7944(00)00196-3
FIGURE 1. A magnified view of fulguration. Although the electrode in the center doesn’t touch the tissue being coagulated, current travels through pathways of ionized air.
rent and coagulation current. Significant overlap exists between them. With the solid-state electrosurgical generators used today, either type of current can produce electrodissection or desiccation. Only coagulation current can produce fulguration. The terms electrodissection, fulguration, and desiccation are not commonly used by clinical surgeons, but are widely used by engineers, sales representatives, and others within the electrosurgical industry.
BRIEF HISTORY OF ELECTROSURGERY Electrosurgical technology is more than 100 years old. At the end of the 19th century, several devices were invented to generate radio-frequency current, largely for the purpose of radio transmissions. The most widely used was the spark gap transmitter, which was the standard radio transmitter for 3 decades before vacuum tubes were invented in the 1920s. The spark gap transmitter was a somewhat crude device. It put out a waveform with a fairly constant frequency that varied greatly in amplitude. One could smooth out the variations in amplitude by feeding the output of the spark gap through a combination of inductors and capacitors, at the cost of some of the power. As crude as it was, the spark gap transmitter functioned well enough to make radio communication a worldwide medium of communication during the first decades of the 20th century. In the 1890s, scientists in France began to explore what would happen if one applied radio-frequency current to tissue. They discovered that the raw output of a spark gap transmitter would coagulate bleeding, and that a “pure,” or smoothed, radio frequency current would cut tissue. The technology was primitive by modern standards, but it was effective. Beginning CURRENT SURGERY • Volume 57/Number 2 • March/April 2000
around the turn of the century, it began to be used in clinical surgery in Europe. Surgeons in the United States began to use the technique in the 1920s. Harvey Cushing, the Boston surgeon who was the father of neurosurgery, is usually credited with introducing electrosurgery to the United States. Actually, many neurosurgeons think he invented electrosurgery. He didn’t, but he did pioneer its use in the brain. He worked closely with Dr. Bovie, an electrical engineer at MIT, who founded a company to make electrosurgical generators. The Bovie Company has long since been swallowed up by other companies, but it dominated the field for about 30 years. And, of course, Dr. Bovie’s name is often used to describe the technology he fostered. Spark gap technology was used first, until the 1940s, when vacuum tube technology came to dominate the field. Interestingly, the spark gap technology was used in medicine for 20 years after it had been abandoned in radio engineering. Transistors were developed in the 1950s, but at first could not handle the high power required for electrosurgery. After the development of the silicon power transistor in the 1960s, most companies switched to solid-state technology. The original electrosurgical generators were waist-high consoles, whereas modern generators are small boxes. Monopolar electrosurgery was the initial form, and it is still the most common. Bipolar electrosurgery has been around since Cushing’s day. Argon-enhanced electrocoagulation (the argon beam coagulator) was developed by 2 or 3 companies in Denver in the 1970s and 1980s. Radio-frequency ablation of tissue, used in cardiology and in oncology, was developed during the 1980s and 1990s. 173
FIGURE 2. Cutting current, as shown on the oscilloscope screen. The Y axis is amplitude, and the X axis is time. Notice that the current is continuous, and that the frequency is about 10 cycles per 20 microseconds—i.e., about 500,000 cycles/second.
BASIC CUTTING AND COAGULATION Electrosurgery uses radio-frequency current in the range of 400,000 to 600,000 Hz (otherwise known as cycles per second). This is around the low end of your AM radio dial. Electrosurgical generators deliver well over 100 w to the patient. Voltages produced by electrosurgical generators range from as low as 100 v to as high as 5000 v. The use of electrical energy at these levels is potentially dangerous. Both cutting and coagulation current use the same frequency. Coagulation current is interrupted some 30,000 or so times per second, producing a chain of very short packets of
radio-frequency energy (Fig. 2). Cutting current is simply a continuous radio-frequency current (Fig. 3). The difference between them appears to be that with cutting current, the continuous current quickly heats individual cells to the point of boiling, and the cells rupture. This rupture divides tissue, and produces a cutting effect. But with coagulation current, the cells cool off during the “off” cycles, and the tissue dries out rather than rupturing. So what is blended cutting? Blended cutting is simply cutting current interrupted at the same rate as coagulation current. But instead of concentrating the generator output into 2 or 3 cycles, like coagulation current, blended cutting lets more cycles
FIGURE 3. Blended cutting, showing that the continuous current is interrupted every 48 microseconds, or about 21,000 times per second. The “on” time is slightly longer than the “off” time. Engineers refer to this as a “duty cycle,” which is about 53% in this case. This cycle is equivalent to blend #1 on most electrosurgical generators. Notice that, although the amplitude (voltage) is the same as in Figure 2, the current delivered by this waveform must be only half of that delivered by the waveform in Figure 1. To keep the power level constant, the generator would increase the voltage delivered by this waveform to twice that shown here. 174
CURRENT SURGERY • Volume 57/Number 2 • March/April 2000
FIGURE 4. Blended cutting, with a “duty cycle” of about 17%. Again, an actual generator would increase the voltage level to keep the power output constant.
through. Blended cutting is basically a cutting current, but with some coagulation effect. The shorter the “packets” of radiofrequency current, the more blended cutting acts like coagulation. “Blend 1” might let 50% of the current through, whereas “Blend 3” might let only 10% through (Figs. 4 and 5). With modern high-voltage, high-wattage electrosurgical generators, either type of current can cut or coagulate, although differences in effectiveness exist. Using coagulation current to cut, for example, produces much more extensive charring and adjacent tissue damage. Fulguration cannot be produced by cutting current, because it lacks the high voltage required.
Cutting current is typically low voltage and high current. This is low voltage only by electrosurgical standards, because the voltage is still more than 100 V. Coagulation current, on the other hand, is typically “on” for only 6% of the time. It has voltage levels 10 to 20 times those of cutting current, for the same power level. Because coagulation produces desiccation and drying of the tissue, the tissue impedance is higher, and the current flow is much lower than electrosurgical cutting. Desiccation is produced when an electrode is held in contact with tissue and current is applied. Either cutting or coagulation current will work, although coagulation current is somewhat
FIGURE 5. Coagulation current, showing that the current is confined to only 3 half-cycles. These pictures all show the same amplitude or voltage. The amount of current delivered during these brief “on” periods is much less than that delivered by cutting current. To deliver the same amount of power, the generator would drive the voltage for the coagulation waveforms to a level 10 or 20 times higher than that used for pure cutting waveforms. CURRENT SURGERY • Volume 57/Number 2 • March/April 2000
175
more rapid. The tissue is dried by the current, and coagulation of blood vessels is produced. Desiccation produces a pale, dry, eschar adjacent to the electrode position. Fulguration is produced when the electrode is held a short distance (2–5 mm) from the tissue, and the spark is allowed to pass from the electrode to the tissue (Fig. 1). Fulguration is typically done with coagulation current. A particular configuration of coagulation current called the “spray mode” is sometimes available on the electrosurgical generator. The reason it works is fairly technical, but the net effect is to allow the electrode to be held a bit further from the tissue. Fulguration typically produces a dark char on top of the tissue, with a fairly superficial eschar that can be effective in producing hemostasis. But if it is not done carefully, with the spark traveling to dry tissue rather than to blood on the top of tissue, fulguration may produce a coagulum of charred blood over the tissue, and it may leave bleeding tissue beneath the coagulum. The ultimate extension of fulguration is argon beam coagulation, in which the electrode is held 5 to 10 mm from the tissue, and the current travels down a “beam” of ionized argon gas to the tissue.
MORE POWER, SCOTTY! Many years ago, electrosurgical generators were adjusted by numbers on the skirt of the plastic dials on the front of the machine. Most generators worked well with the dials adjusted to 3 (of 10). Today, digital readouts are used. They indicate power level, in watts. Measuring the power level depends on multiplying current times voltage, and adjusting for the duty cycle (Figs. 2 and 4). Separate indicators almost always exist for cutting and coagulation currents. In theory, we have the ability to adjust the generators much more precisely and to use separate adjustments. However, old habits die hard. Most of us, and most operating room personnel, still use the old 3 of 10, only we now use “30” on the power readout. So we adjust both cutting and coagulation to “30 w,” and go about our business. Unfortunately, 30 w is barely adequate for coagulation current, and totally inadequate for cutting current. So most surgeons use coagulation current for everything, including cutting, and don’t understand why their electrosurgery doesn’t work particularly well. The secret to using cutting current is to adjust it to 60 w. In fatty tissue, which conducts current less well than muscle or fibrous tissue, it may be best to go to 80 w. Of course, some difference exists among the different brands of generators. But they all use watts as their unit of output, and this produces a fair amount of standardization.
BASIC ELECTROSURGICAL SAFETY Most electrosurgical injuries occur at the ground pad. Now, electrosurgery has come a long way since the days when the ground pad was a metal plate with contact gel smeared on it. The current ground pad isn’t even called a ground pad. It’s now a dispersive electrode. To understand the changes and the safety features, we need to review how monopolar electrosurgery works from an electrical standpoint. 176
Electrosurgery places the patient’s body in an electrical circuit. Current travels from the generator, through a wire to the electrosurgical pencil electrode, and into the patient at the operative site. From the operative site, the current then travels through the patient’s body to the dispersive electrode, and then through a wire back to the generator to complete the circuit. Now, the idea is to concentrate the current at the tip of the pencil electrode to produce the desired effect, and to keep the current dispersed everywhere else to avoid damage anywhere else. When the current is allowed to concentrate anywhere else, accidents happen. Where are the likely sites of accidents? If someone steps on the pedal, the pencil can be turned on, and burn through the drapes, or burn the patient somewhere away from the operative site. Using a pencil with a button on the pencil avoids this hazard. But we still use a pedal during laparoscopy. One may use the wrong pedal, or hit the wrong button, but this usually is not a serious error. Usually. What else? The surgeon can produce an error simply by applying electrosurgery to the wrong structure. An example might be “buzzing” too near a major nerve. A large malpractice judgment occurred in Maryland from a case in which a chest surgeon coagulated bleeding too close to an intervertebral foramen and injured the spinal cord. A number of bowel injuries have been produced by laparoscopic surgeons, especially during the early days of laparoscopy. The laparoscopic surgeon must be careful to use electrocoagulation only within the field that can be seen on the monitor, to use the least voltage feasible by using cutting current for desiccation, keeping the power levels down, and so on. Laparoscopic surgery is a complex environment from an electrical standpoint, and it will be dealt with more completely in a subsequent article in this series. When the electrosurgical current diffuses out through the body, it can concentrate in unintended ways. Current travels preferentially down blood vessels, because arteries and veins have lower impedance than other structures. (I know that may be an unfamiliar term, but we’ll deal with impedance in the next article in the series.) So, consider a situation in which a structure— bowel, for example—is connected to the rest of the body through a thin vascular pedicle. Applying electrosurgical current to the bowel may result in damage to the vascular supply. And don’t be fooled by fat. Fat has high impedance (there’s that word again), and it does not dissipate current well at all. And then we come to the dispersive electrode. In the old days, the ground pad was simply a metal plate with conductive goo spread over it. During a long operation, the conductive paste would dry, and stop conducting. This process would concentrate the current into a small portion of the ground pad and produce a burn on the skin. Modern dispersive electrodes are fairly complex devices. Not only are they designed so the conductive gel doesn’t dry out, but they also have a built-in self-testing system, so that the electrosurgical generator can monitor the status of the dispersive electrode and shut down if the dispersive electrode dries, becomes loose, or otherwise presents a danger to the patient. Safety during electrosurgery rests on a knowledge how electrical energy interacts with the patient. Although great imCURRENT SURGERY • Volume 57/Number 2 • March/April 2000
provements have occurred over the past decade in making safer generators, electrosurgery still has the potential for causing damage to patients.
CONCLUSIONS Electrosurgery is an extremely valuable technology. It is no exaggeration to say that modern surgery would be impossible without it. An increased knowledge of the technology will bring great rewards in the ability of the surgeon to use electrosurgery more effectively as well as more safely.
CURRENT SURGERY • Volume 57/Number 2 • March/April 2000
FURTHER READING ECRI. Electrosurgical units. Health Devices 1997;26:400 – 410. The Toronto Hospital. Aspects of electrosurgery [CD-ROM]. Denver: Education Design, 1998. Voyles CR, Tucker RD. Education and engineering solutions for potential problems with monopolar electrosurgery at laparoscopy. Am J Surg 1992;164:57– 62. Voyles CR, Tucker RD. Essentials of monopolar electrosurgery for laparoscopy. Electrosurgical concepts. Boulder, Colo: Valley Lab, Inc, 1992.
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Electrosurgery 101 Charles W. Van Way III, MD Department of Medical Education, St. Luke’s Hospital, Kansas City, Missouri INTRODUCTION: THE UNEXPLORED COUNTRY Electrosurgical technology is a basic part of operative surgery. Few surgeons will operate without using it. And yet, basic principles and practical applications of electrosurgery are poorly understood. Unhappily, most surgeons minimize the importance of electrosurgery. We don’t understand it, and we don’t particularly think we need to understand it. We just use it. More particularly, residents are not given formal instruction in its use. Operating room personnel are usually trained by the manufacturer’s representatives. Most surgeons rely on operating room nursing personnel when setting up electrosurgical equipment. That is to say, we rely on people trained by sales representatives. Actually, the sales representatives are responsible individuals and well trained on the equipment. It would be nice if surgical residents knew as much as the average representative. Now, operating room personnel do their best. But even people doing their best can make mistakes. Injuries resulting from electrosurgery are the most common reason for malpractice suits against hospitals, resulting from operations. OK, so we don’t know enough. But, what should we know? On the theoretical side, it would be good to understand the difference between cutting and coagulation current, as well as the characteristics of radio-frequency current used in electrosurgery. On the practical side, it is important to know about the differing varieties, such as fulguration and desiccation, to be able to tell operating room personnel how to adjust the equipment, to identify common hazards, and to know how to prevent injuries. Electrosurgical technology is neither self-evident nor inherently safe. Injuries resulting from electrosurgery may be catastrophic. As an extreme example, some years ago, a patient being operated on in a large West Coast teaching hospital caught on fire and died. Electrosurgery was being used at the time. The professor and the resident didn’t have a clue as to what happened. The fire was probably caused by arcing at the dispersive electrode—the “ground pad”— or it may have been
Correspondence: Inquiries to Charles W. Van Way III, MD, Dept. of Medical Education, St. Luke’s Hospital, 4401 Wornall Road, Kansas City, MO 64111; fax: (816) 932-5179; e-mail: [email protected]
172
caused by equipment failure. Both the surgeons and the hospital were successfully sued. This paper is intended to be the first of a series, whose purpose will be to provide the background and the basics of electrosurgery. The first installment will discuss basic electrosurgical coagulation and cutting, and have a few words about safety. Subsequent papers will discuss electrosurgical physics, the use of electrosurgery in laparoscopic surgery, and new technologies. Several new technologies exist, including the argon beam coagulator, Faraday shield technology to prevent injury during laparoscopy, and radio-frequency destruction of tissue in cardiology and surgical oncology.
WHAT’S IN A NAME? The proper name of the technology is electrosurgery. The term “electrocautery” is often used. Actually, electrocautery refers to the use of electricity to heat an iron to be used as a hot cautery. One might compare it to a surgical soldering iron. Electrosurgery is most commonly monopolar, in which a single electrode is used, and the return circuit is through a dispersive pad (ground pad, to most of us). Monopolar electrosurgery can produce both coagulation and cutting. Bipolar electrosurgery uses a type of forceps in which the current passes between the arms of the forceps. It is used widely in neurosurgery. Bipolar electrosurgery is limited to coagulation mode. Other names are used to describe the modes of electrosurgery, which depend to some extent on the type of current used. Electrodissection is use of electrosurgery to divide tissue; i.e., cutting. Electrocoagulation is electrosurgery in its coagulation mode, used for hemostasis. Two major types of electrocoagulation, fulguration and desiccation, exist. Both types refer to coagulation of tissue produced by monopolar electrosurgery. In desiccation, the electrode is held in contact with the tissue or with a clamp to produce a zone of coagulation by direct contact. In fulguration, the electrode is held slightly above the tissue, so that the current travels across a gap to reach the tissue. The current actually travels through air by ionizing the nitrogen, creating a current path from the electrode to the tissue. The ionized current path lasts for only a few milliseconds, so that the appearance of an electrode during fulguration shows multiple ionization pathways. It looks like multiple miniature lightening strikes: (Fig. 1). Two types of current are used in electrosurgery: cutting cur-
CURRENT SURGERY • © 2000 by the Association of Program Directors in Surgery Published by Elsevier Science Inc.
0149-7944/00/$20.00 PII S0149-7944(00)00196-3
FIGURE 1. A magnified view of fulguration. Although the electrode in the center doesn’t touch the tissue being coagulated, current travels through pathways of ionized air.
rent and coagulation current. Significant overlap exists between them. With the solid-state electrosurgical generators used today, either type of current can produce electrodissection or desiccation. Only coagulation current can produce fulguration. The terms electrodissection, fulguration, and desiccation are not commonly used by clinical surgeons, but are widely used by engineers, sales representatives, and others within the electrosurgical industry.
BRIEF HISTORY OF ELECTROSURGERY Electrosurgical technology is more than 100 years old. At the end of the 19th century, several devices were invented to generate radio-frequency current, largely for the purpose of radio transmissions. The most widely used was the spark gap transmitter, which was the standard radio transmitter for 3 decades before vacuum tubes were invented in the 1920s. The spark gap transmitter was a somewhat crude device. It put out a waveform with a fairly constant frequency that varied greatly in amplitude. One could smooth out the variations in amplitude by feeding the output of the spark gap through a combination of inductors and capacitors, at the cost of some of the power. As crude as it was, the spark gap transmitter functioned well enough to make radio communication a worldwide medium of communication during the first decades of the 20th century. In the 1890s, scientists in France began to explore what would happen if one applied radio-frequency current to tissue. They discovered that the raw output of a spark gap transmitter would coagulate bleeding, and that a “pure,” or smoothed, radio frequency current would cut tissue. The technology was primitive by modern standards, but it was effective. Beginning CURRENT SURGERY • Volume 57/Number 2 • March/April 2000
around the turn of the century, it began to be used in clinical surgery in Europe. Surgeons in the United States began to use the technique in the 1920s. Harvey Cushing, the Boston surgeon who was the father of neurosurgery, is usually credited with introducing electrosurgery to the United States. Actually, many neurosurgeons think he invented electrosurgery. He didn’t, but he did pioneer its use in the brain. He worked closely with Dr. Bovie, an electrical engineer at MIT, who founded a company to make electrosurgical generators. The Bovie Company has long since been swallowed up by other companies, but it dominated the field for about 30 years. And, of course, Dr. Bovie’s name is often used to describe the technology he fostered. Spark gap technology was used first, until the 1940s, when vacuum tube technology came to dominate the field. Interestingly, the spark gap technology was used in medicine for 20 years after it had been abandoned in radio engineering. Transistors were developed in the 1950s, but at first could not handle the high power required for electrosurgery. After the development of the silicon power transistor in the 1960s, most companies switched to solid-state technology. The original electrosurgical generators were waist-high consoles, whereas modern generators are small boxes. Monopolar electrosurgery was the initial form, and it is still the most common. Bipolar electrosurgery has been around since Cushing’s day. Argon-enhanced electrocoagulation (the argon beam coagulator) was developed by 2 or 3 companies in Denver in the 1970s and 1980s. Radio-frequency ablation of tissue, used in cardiology and in oncology, was developed during the 1980s and 1990s. 173
FIGURE 2. Cutting current, as shown on the oscilloscope screen. The Y axis is amplitude, and the X axis is time. Notice that the current is continuous, and that the frequency is about 10 cycles per 20 microseconds—i.e., about 500,000 cycles/second.
BASIC CUTTING AND COAGULATION Electrosurgery uses radio-frequency current in the range of 400,000 to 600,000 Hz (otherwise known as cycles per second). This is around the low end of your AM radio dial. Electrosurgical generators deliver well over 100 w to the patient. Voltages produced by electrosurgical generators range from as low as 100 v to as high as 5000 v. The use of electrical energy at these levels is potentially dangerous. Both cutting and coagulation current use the same frequency. Coagulation current is interrupted some 30,000 or so times per second, producing a chain of very short packets of
radio-frequency energy (Fig. 2). Cutting current is simply a continuous radio-frequency current (Fig. 3). The difference between them appears to be that with cutting current, the continuous current quickly heats individual cells to the point of boiling, and the cells rupture. This rupture divides tissue, and produces a cutting effect. But with coagulation current, the cells cool off during the “off” cycles, and the tissue dries out rather than rupturing. So what is blended cutting? Blended cutting is simply cutting current interrupted at the same rate as coagulation current. But instead of concentrating the generator output into 2 or 3 cycles, like coagulation current, blended cutting lets more cycles
FIGURE 3. Blended cutting, showing that the continuous current is interrupted every 48 microseconds, or about 21,000 times per second. The “on” time is slightly longer than the “off” time. Engineers refer to this as a “duty cycle,” which is about 53% in this case. This cycle is equivalent to blend #1 on most electrosurgical generators. Notice that, although the amplitude (voltage) is the same as in Figure 2, the current delivered by this waveform must be only half of that delivered by the waveform in Figure 1. To keep the power level constant, the generator would increase the voltage delivered by this waveform to twice that shown here. 174
CURRENT SURGERY • Volume 57/Number 2 • March/April 2000
FIGURE 4. Blended cutting, with a “duty cycle” of about 17%. Again, an actual generator would increase the voltage level to keep the power output constant.
through. Blended cutting is basically a cutting current, but with some coagulation effect. The shorter the “packets” of radiofrequency current, the more blended cutting acts like coagulation. “Blend 1” might let 50% of the current through, whereas “Blend 3” might let only 10% through (Figs. 4 and 5). With modern high-voltage, high-wattage electrosurgical generators, either type of current can cut or coagulate, although differences in effectiveness exist. Using coagulation current to cut, for example, produces much more extensive charring and adjacent tissue damage. Fulguration cannot be produced by cutting current, because it lacks the high voltage required.
Cutting current is typically low voltage and high current. This is low voltage only by electrosurgical standards, because the voltage is still more than 100 V. Coagulation current, on the other hand, is typically “on” for only 6% of the time. It has voltage levels 10 to 20 times those of cutting current, for the same power level. Because coagulation produces desiccation and drying of the tissue, the tissue impedance is higher, and the current flow is much lower than electrosurgical cutting. Desiccation is produced when an electrode is held in contact with tissue and current is applied. Either cutting or coagulation current will work, although coagulation current is somewhat
FIGURE 5. Coagulation current, showing that the current is confined to only 3 half-cycles. These pictures all show the same amplitude or voltage. The amount of current delivered during these brief “on” periods is much less than that delivered by cutting current. To deliver the same amount of power, the generator would drive the voltage for the coagulation waveforms to a level 10 or 20 times higher than that used for pure cutting waveforms. CURRENT SURGERY • Volume 57/Number 2 • March/April 2000
175
more rapid. The tissue is dried by the current, and coagulation of blood vessels is produced. Desiccation produces a pale, dry, eschar adjacent to the electrode position. Fulguration is produced when the electrode is held a short distance (2–5 mm) from the tissue, and the spark is allowed to pass from the electrode to the tissue (Fig. 1). Fulguration is typically done with coagulation current. A particular configuration of coagulation current called the “spray mode” is sometimes available on the electrosurgical generator. The reason it works is fairly technical, but the net effect is to allow the electrode to be held a bit further from the tissue. Fulguration typically produces a dark char on top of the tissue, with a fairly superficial eschar that can be effective in producing hemostasis. But if it is not done carefully, with the spark traveling to dry tissue rather than to blood on the top of tissue, fulguration may produce a coagulum of charred blood over the tissue, and it may leave bleeding tissue beneath the coagulum. The ultimate extension of fulguration is argon beam coagulation, in which the electrode is held 5 to 10 mm from the tissue, and the current travels down a “beam” of ionized argon gas to the tissue.
MORE POWER, SCOTTY! Many years ago, electrosurgical generators were adjusted by numbers on the skirt of the plastic dials on the front of the machine. Most generators worked well with the dials adjusted to 3 (of 10). Today, digital readouts are used. They indicate power level, in watts. Measuring the power level depends on multiplying current times voltage, and adjusting for the duty cycle (Figs. 2 and 4). Separate indicators almost always exist for cutting and coagulation currents. In theory, we have the ability to adjust the generators much more precisely and to use separate adjustments. However, old habits die hard. Most of us, and most operating room personnel, still use the old 3 of 10, only we now use “30” on the power readout. So we adjust both cutting and coagulation to “30 w,” and go about our business. Unfortunately, 30 w is barely adequate for coagulation current, and totally inadequate for cutting current. So most surgeons use coagulation current for everything, including cutting, and don’t understand why their electrosurgery doesn’t work particularly well. The secret to using cutting current is to adjust it to 60 w. In fatty tissue, which conducts current less well than muscle or fibrous tissue, it may be best to go to 80 w. Of course, some difference exists among the different brands of generators. But they all use watts as their unit of output, and this produces a fair amount of standardization.
BASIC ELECTROSURGICAL SAFETY Most electrosurgical injuries occur at the ground pad. Now, electrosurgery has come a long way since the days when the ground pad was a metal plate with contact gel smeared on it. The current ground pad isn’t even called a ground pad. It’s now a dispersive electrode. To understand the changes and the safety features, we need to review how monopolar electrosurgery works from an electrical standpoint. 176
Electrosurgery places the patient’s body in an electrical circuit. Current travels from the generator, through a wire to the electrosurgical pencil electrode, and into the patient at the operative site. From the operative site, the current then travels through the patient’s body to the dispersive electrode, and then through a wire back to the generator to complete the circuit. Now, the idea is to concentrate the current at the tip of the pencil electrode to produce the desired effect, and to keep the current dispersed everywhere else to avoid damage anywhere else. When the current is allowed to concentrate anywhere else, accidents happen. Where are the likely sites of accidents? If someone steps on the pedal, the pencil can be turned on, and burn through the drapes, or burn the patient somewhere away from the operative site. Using a pencil with a button on the pencil avoids this hazard. But we still use a pedal during laparoscopy. One may use the wrong pedal, or hit the wrong button, but this usually is not a serious error. Usually. What else? The surgeon can produce an error simply by applying electrosurgery to the wrong structure. An example might be “buzzing” too near a major nerve. A large malpractice judgment occurred in Maryland from a case in which a chest surgeon coagulated bleeding too close to an intervertebral foramen and injured the spinal cord. A number of bowel injuries have been produced by laparoscopic surgeons, especially during the early days of laparoscopy. The laparoscopic surgeon must be careful to use electrocoagulation only within the field that can be seen on the monitor, to use the least voltage feasible by using cutting current for desiccation, keeping the power levels down, and so on. Laparoscopic surgery is a complex environment from an electrical standpoint, and it will be dealt with more completely in a subsequent article in this series. When the electrosurgical current diffuses out through the body, it can concentrate in unintended ways. Current travels preferentially down blood vessels, because arteries and veins have lower impedance than other structures. (I know that may be an unfamiliar term, but we’ll deal with impedance in the next article in the series.) So, consider a situation in which a structure— bowel, for example—is connected to the rest of the body through a thin vascular pedicle. Applying electrosurgical current to the bowel may result in damage to the vascular supply. And don’t be fooled by fat. Fat has high impedance (there’s that word again), and it does not dissipate current well at all. And then we come to the dispersive electrode. In the old days, the ground pad was simply a metal plate with conductive goo spread over it. During a long operation, the conductive paste would dry, and stop conducting. This process would concentrate the current into a small portion of the ground pad and produce a burn on the skin. Modern dispersive electrodes are fairly complex devices. Not only are they designed so the conductive gel doesn’t dry out, but they also have a built-in self-testing system, so that the electrosurgical generator can monitor the status of the dispersive electrode and shut down if the dispersive electrode dries, becomes loose, or otherwise presents a danger to the patient. Safety during electrosurgery rests on a knowledge how electrical energy interacts with the patient. Although great imCURRENT SURGERY • Volume 57/Number 2 • March/April 2000
provements have occurred over the past decade in making safer generators, electrosurgery still has the potential for causing damage to patients.
CONCLUSIONS Electrosurgery is an extremely valuable technology. It is no exaggeration to say that modern surgery would be impossible without it. An increased knowledge of the technology will bring great rewards in the ability of the surgeon to use electrosurgery more effectively as well as more safely.
CURRENT SURGERY • Volume 57/Number 2 • March/April 2000
FURTHER READING ECRI. Electrosurgical units. Health Devices 1997;26:400 – 410. The Toronto Hospital. Aspects of electrosurgery [CD-ROM]. Denver: Education Design, 1998. Voyles CR, Tucker RD. Education and engineering solutions for potential problems with monopolar electrosurgery at laparoscopy. Am J Surg 1992;164:57– 62. Voyles CR, Tucker RD. Essentials of monopolar electrosurgery for laparoscopy. Electrosurgical concepts. Boulder, Colo: Valley Lab, Inc, 1992.
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