Abstract
Electrosurgery is a ubiquitous technology in common use in laparoscopic and open surgery across all surgical disciplines. While this technology is safe when used properly, a potential exists for unintended delivery of energy through multiple mechanisms. Proper understanding of basic electrophysics is important to understanding the basic mechanisms of failure. We present a review of these basic concepts, as well as multiple case vignettes of surgical complications with explanations of the described principles. (J GYNECOL SURG 38:264)
Introduction
Worldwide, gynecologic surgery is increasingly performed through the use of laparoscopic and robotic techniques. First developed in the 1920s, the routine use of radiofrequency electrosurgery has become ubiquitous. Every medical student remembers the excitement of the first time he or she was handled the mystical “Bovie” and told to “buzz that bleeder!” While electrosurgical tools give us tremendous ability to create hemostasis and safely cut through tissues, use of these tools is not without risk.
Safe use of electrosurgery depends on a surgical team's clear understanding of this surgery's mechanisms and functions. While many different electrical principles govern how electrosurgical complications occur, ultimately, they derive from the fundamental pathway of energy delivered to an unintended place. This may occur by spread of electrosurgical heat, by direct application of electrical energy to unintended structures, or by diversion of the actual stream of energy through an unintended electrical pathway. A surgeon who hopes to minimize electrosurgical complications must understand all of these mechanisms of potential failure in order to avoid them.
In this article, we present the basic principles of electrosurgery and examine specific case vignettes involving electrosurgical complications to illustrate mechanisms of injury best. We then then explore the root causes of injuries related to electrosurgical techniques by describing prototypical complications, why they occur, and how best to prevent them.
A Little History
An interest in the use of electrosurgery dates to the 1800s when Philipp Bozzini (Doctor of Medicine; 1773–1809
Today, these units have become “miniature” further, and often serve multiple functions, including simple monopolar energy delivery, and bipolar energy delivery, and, often, have impedance-measured bipolar “smart energy” devices, all in the same unit. Ultimately, all of these units function similarly and operate using the same electrical principles.
Principles of Electrosurgery
The term electrocautery is sometimes used interchangeably with electrosurgery; yet this is technically incorrect. Cautery refers to the application of heat directly to tissue. Electrocautery is the use of electricity to heat a resistive electrode and, in turn, create what is effectively a “hot poker.” Electrocautery has been used in surgery in the past, and, in fact, preceded the use of electrosurgery by more than 100 years, first being used by Alexandre-Edmond Becquerel (physicist; 1820–1891
Electrosurgery refers to the creation of an electrical circuit including an electrosurgical generator, an electrode, and the patient. By directing electrons through a small interface between electrode and patient, electrosurgery can affect many different functions including cutting, coagulating, desiccating, and fulgurating.
The flow of electrons through a circuit is referred to as current (I). This current is akin to a volume of water flowing down a river, with a measurement of that current being equal to that volume crossing a given point over a given time period. This is most commonly measured in amperes (A).
Voltage (V) refers to the electrical force that pushes electrons through a circuit. Think of it as the height of the waterfall that a river goes over. In the case of hydroelectric power, it is that fall in the water that is harnessed to generate power. In the same way, the fall in electrical state of electrons is the power we deliver to tissue in electrosurgery. While we cannot control voltage directly in electrosurgery, the electrosurgical generator varies the voltage it delivers in order to control power.
Resistance (R) is how difficult it is to push electrons through a circuit. In the river, resistance is effectively the width and depth of the river, or the total area that the water can flow though at any point. In electrosurgery, we can control resistance by touching tissue with a very small electrode (high resistance), or with a bigger electrode surface (lower resistance). Different tissues also have different resistances. For example, fat has high resistance, while blood vessels (being full of fluid) have much lower resistance.
Power (P) is the total amount of electrical energy delivered per time. The unit watts (W) is 1 Joule/second. In the water example, power is the total kinetic energy released in the river flowing. In electrosurgery, power is the one thing we can control directly via the mechanisms on the generator box. For example, if you set your monopolar generator to 30 on cut and 30 on coagulation, you are telling the box that when you activate it, you want 30 W of power. You, in turn, will create the resistance by the way you use your instrument, and then the box will vary voltage to attempt to give you the power you requested.
Three of these elements come together in Ohm's law: V = I × R (voltage equals current times resistance). The fourth element of power comes together in the formula P = I × V (power is current times voltage). In order for the electrosurgical generator to give you the power you ask for, it has to vary the voltage until the current rises enough to deliver that level of power, depending on the resistance of the circuit you are creating.
In addition to varying voltage to achieve a specified power, an electrosurgical generator can also vary the waveform of the electricity to achieve different types of energy effects.
We are all familiar with cut and coagulation. Cut is a continuous sine wave of electricity, with electrons flowing forward and backward through the circuit in rhythmic synchrony, with a relatively low voltage. It cuts because the electrons are sawing up and back at relatively low energy, effectively vaporizing tissue without a lot of heat. Coagulation is an intermittent delivery of a relatively higher voltage current. Instead of the continuous “up and back” of an electron saw, coagulation can be thought of as an intermittent series of electron explosions with nothing in between. Coagulation puts down heat and burns tissue, and, for small enough vessels, can seal them. With enough countertraction, coagulation will also cut through tissue as it coagulates. Most generators also have blend settings that split the difference. Some advanced generators also have variants of coagulation currents that “spray,” which creatures more surface fulguration.
Monopolar Versus Bipolar Energy
We are also familiar with monopolar versus bipolar energy. Some people may think of these as 2 different things requiring different considerations, but they actually are the same thing. The only difference is the size and location of the electrodes. Monopolar fires energy through a small delivery electrode and the energy returns through a larger return electrode pad on the patient's back or thigh. Bipolar fires from one side of a small electrode and returns from another electrode on the same instrument. We use these devices for different things, but the same principles apply, and by applying them we can predict the behavior of the instrument.
Herein now are some prototypical case vignettes that illustrate these points and their clinical implications. All of these case vignettes are theoretical, and, thus, no specific patient consents were obtained.
Case Vignettes Involving Electrosurgical Complications
Case vignette #1
A 35-year-old female with a 6-cm right ovarian dermoid cyst undergoes laparoscopic surgery for ovarian cystectomy. At the time of surgery, she has moderate pelvic adhesions involving the right ovary, posterior uterus, and right pelvic sidewall. The surgeon uses a nondisposable monopolar-scissors device. The surgeon uses monopolar settings set at 100 W cut and 50 W coagulation. There were no bowel adhesions and, at the time of surgery, and so, the bowel was swept away from the pelvis during lysis of adhesions and for the cystectomy. Estimated blood loss for the surgery was 50 mL and the patient was discharged to go home on the day of surgery after an uncomplicated course in the recovery unit.
Four days later, she presents to the emergency department complaining of abdominal distention, loss of appetite, pain, and a temperature of 102.3°F. Computed tomography (CT) of her abdomen and pelvis reveals an abscess near the transverse colon and evidence of free air. Blood analysis shows leukocytosis with 19.6% white blood cells. An examination reveals a rigid abdomen with peritoneal signs. Surgical evaluation reveals a perforation of the small bowel in the upper abdomen, far from the surgical field.
What happened:
This case is an example of an electrosurgical injury occurring due to insulation failure or direct coupling. Injuries such as this may be unrecognized at the time of surgery due to occurring outside the field of view (FOV).
Insulation failure has been seen in 3%–39% of laparoscopic instruments, and most bowel injuries are unrecognized at the time of surgery. 4 In an ex-vivo study using porcine jejunum, Martin et al. showed that a small amount of energy leaked from standard instruments could cause full thickness injury. 5
In a retrospective meta-analysis by Llarena et al. from 2015, 29% of bowel injuries were` mediated by electrosurgical damage during laparoscopic hysterectomies. 6 Delayed recognition of injury is particularly significant as it increases morbidity. This can be more likely with a thermal bowel injury due to direct coupling or insulation failure outside of the FOV.
It is important to understand that, when a surgeon presses the monopolar pedal, that surgeon is instructing the device to try to complete a circuit. If resistance at the target is too high because of a significant air gap between the tips of the scissors and other grounded tissue, the generator will increase voltage until it hits a set maximum. 7 Even small defects in insulation create a potential path for electrons to complete a circuit, and, if this occurs, substantial thermal and electrical damage can occur to unintended surfaces. 8 When a patient is in a Trendelenburg position, the ileum and jejunum, or transverse or descending colon may be near enough to the shaft of a monopolar device to complete a circuit through such a defect, leading to bowel injury.
When using any monopolar device, it should be routine practice to inspect the device to make sure there are no defects in the insulation. While this should also be done by the scrub technicians and sterile-processing technicians, the surgeon is the last line of defense. Some hospitals also use disposable instruments, which increase costs but decrease the likelihood of insulation failures.
Some people may have the impression that insulation is absolute and that any amount of nonconductive material will prevent a circuit from being established. This is a misconception. Your sneakers will not protect you from a lightning bolt, as the voltage and current involved will laugh at the ½ inch of nonconductive rubber. It is all relative. Many of us remember the early scissor-tip insulators on the Da Vinci monopolar device, which frequently failed in the face of the currents being applied. The devices were not damaged, but they, in the end, just did not have enough insulation material to prevent currents from breaking through them. Insulation is resistance to current flow, not a brick wall.
In many cases, higher power enables more-precise delivery of energy at the surgical site, with faster cutting and less duration of energy activation. As such, the adage of “use the lowest power possible” may not truly apply when it comes to the actual surgical site. Where this does apply, is in the potential for stray current. The higher you set the power, the more energy you give the generator to find an alternate circuit when there is no distal circuit available at the instrument tip. If there is a weak spot in the insulation, higher power will make it easier for stray power to break through insulation and form an alternate circuit, or even to break through entirely intact but inadequate insulation.
Case vignette #2
A surgeon is doing a beautiful robotic hysterectomy for a 12-week-size fibroid uterus. The superior pedicles have been taken down, and it is time to seal the uterine arteries. After taking down the anterior and posterior leaves of the broad ligament, the surgeon grasps the right uterine artery and surrounding fat with a left-sided bipolar device above the colpotomy ring, sealing the vessel in several locations. It takes several applications to seal the vessel fully, and after transection, there is some bleeding from the vessel requiring additional application of the bipolar device. After the hysterectomy, a cystoscopy is performed and there is efflux of urine from both ureteral orifices.
Three days later, the patient presents to the office with right-flank pain. A CT shows hydronephrosis and hydroureter without urinoma. A urologist is able to place a stent and, in time, the ureteral injury resolves.
What happened:
A bipolar device functions by firing electrons from one paddle to the other through the intervening tissue. This process creates heat, and, in continuous application, the heat will continue to spread circumferentially from the point of application for the duration of activation. Increasing resistance of the tissue also will demand longer application of current at a higher voltage, creating more heat than sealing less-resistive tissue. Skeletonization of the uterine artery is critical for creating minimal resistance. As fat has high resistance, failing to “de-fat” the uterine pedicle fully will force the generator to apply greater voltage to achieve the specified power, creating more heat. It also will create the conditions for an inadequate seal, in turn, requiring reapplication of energy, again, using more heat. Often, this reapplication is more lateral than the initial seal, again, increasing the chances of a thermal injury to the ureter. Failing to remove the anterior and posterior peritoneum and attempting to seal through these tissues will also lead to higher voltage and longer application of energy, again creating more heat.
The optimal application of bipolar to a uterine artery is at the isthmus at the edge of—or above—a properly installed colpotomy ring. In robotic cases, the bipolar will come from the contralateral side on 1 of the uterine arteries. When a uterus is large, this can force a suboptimal placement of the bipolar, both in terms of laterality and also in terms of a larger pedicle of tissue (in turn, requiring more energy). The answer to this problem is to identify when the contralateral arm is forcing suboptimal placement and to switch the arms before firing the energy.
The use of smart bipolar devices takes advantage of a generator's ability to measure resistance/impedance continuously as the device is activated, continuously varying current to achieve an optimal seal while delivering the minimum amount of energy required. These devices produce less thermal spread and, in many cases, also create a tighter seal to tissue than a more-conventional bipolar device. These devices may be branded systems (i.e., Medtronic LigaSuretm), or may be specific generators that can be coupled to a generic bipolar device (i.e., ERBE). In general, the use of these devices is preferred over raw bipolar, when available.
Case vignette #3
A surgeon is removing endometriosis using monopolar shears on coagulation current, while an assistant is retracting the bowel and clearing smoke with a suction irrigator. At times, the surgeon fires the monopolar too far from tissue to create a circuit, and there is arcing to the irrigator tip. A visible burn is seen on the sigmoid colon where the suction irrigator touched it. A colorectal surgeon is called, and the bowel is oversewn, with no long-term complications.
What happened:
Direct coupling occurs when a monopolar electrode is allowed to create a circuit with another conductive device on, in, or near the patient. In this case, the suction irrigator is a metal device that is highly conductive and entirely able to create a circuit with the monopolar. Furthermore, the application of power while the monopolar electrode is not near enough to tissue to create a circuit creates high resistance to the target tissue, and is “daring” the current to find a new way back to the generator. The other important element is that the base of the suction irrigator is made of plastic and, thus, is highly resistive. So, if you charge the suction irrigator, current will travel through the irrigator tip and then return through whatever conductive tissue it touches, in this case, the bowel that is being retracted.
Direct coupling may also occur if one manages to charge a metal port or cannula with a monopolar instrument. Fortunately, this is unlikely to cause a problem as the cannula has a large surface area connection to the patient and thus current will return through the abdominal wall, even if the cannula did touch other tissue.
One may also create direct coupling in open surgery by accidentally charging a metal retractor. Given an adequately small connection to the patient, this may also create a burn.
Direct coupling is something we also do on purpose. Grasping a bleeder with a hemostat and touching the activated electrosurgery pencil to the hemostat is creating a direct coupling. While this is relatively safe, the use of cut current when doing this reduces energy while providing a similar, if not superior, hemostatic seal. Ideally one should couple to the hemostat past the point of contact with the surgeon's hands, as otherwise (similar to case #1), we are again daring electrons to find a path home through the surgeon's gloves.
Case vignette #4
A surgeon fires a monopolar scissors without creating a distal connection, while using a mixed-material port. A bowel injury is later found.
What happened:
This is an example of capacitive coupling. We will not belabor this electrically complex situation here, as modern equipment has largely made this a thing of the past. In short, capacitive coupling allows a current to flow between 2 circuits that are not actually touching, using their intervening magnetic fields as a medium. This is how your phone charges wirelessly as well. This was a problem in the past because of ports that were made of both plastic and metal, creating a potential capacitor. Today, ports are either entirely metal or entirely plastic. Plastic ports will not act as capacitors, and metal ports are fully grounded to the patient and, as such, capacitive current will not escape to other surfaces.
Each of these cases follows a common theme: the delivery of energy to unintended tissue. Electrosurgery is a versatile and powerful tool, but like any tool requires proper understanding and skill to use properly.
Case vignette #5
A thin woman undergoes a laparoscopic hysterectomy. The return electrode is placed over her hip. At the end of the surgery, a full-thickness burn is found under the return electrode
What happened:
The return electrode functions by providing a large conductive surface to allow return of electrons to the electrosurgery unit. While most electrosurgery systems will detect a return pad that is losing its adherence through automatic-detection systems, a return electrode placed over a very thin patch of tissue will continue to function. Placing a pad over an area that brings current through a very small bit of tissue (the tiny bit of fat over the iliac crest of a thin patient, for example), is asking energy to travel through an area of high resistance, creating heat. Furthermore, such burns can be deep and require substantial intervention to heal.
Tips and Techniques for Prevention of Electrosurgical Injuries
A number of strategies have been outlined by many researchers. 9 We offer you a consolidated list of the best tips.
Use the lowest-possible power settings.
Favor a low-voltage waveform (cut).
Skeletonize vessels before applying bipolar coagulation.
When sweeping bowel out of the FOV, check to be sure your instruments will not be resting on it (prevent direct coupling to unintended instruments).
Favor bipolar electrosurgery over monopolar when appropriate.
Avoid initiating current when the device is not in contact with the tissue.
Use brief intermittent activation whenever possible to reduce buildup of heat.
Know your patient's anatomy and isolate structures before applying energy.
Always place return electrodes over fleshy portions of the body, such as the back or thigh.
Conclusions
Electrosurgery is a versatile and powerful surgical technology which, like all energy delivery, carries with it risks of complications. The common pathway of complications is delivery of energy to the wrong tissues, either through spread of heat, through direct coupling, capacitive coupling, or through insulation failure. Understanding each of these pathways of failure, and how to avoid them, is critical to safe use of the technology.
Footnotes
Authors' Contributions
Both authors were actively involved in the drafting, editing, and completion of this article.
Author Disclosure Statement
No financial conflicts of interest exist.
Funding Information
No external funding was received for preparation of this article.