Principles of Electrosurgery

Principles of Electrosurgery

David L. Carr‐Locke1 and John Day2

1 Weill Cornell Medicine, New York, NY, USA

2 Erbe USA Inc., Marietta, GA, USA

Learn and understand electrosurgery

It is potentially the most dangerous tool we use in endoscopy


Electrosurgery is the medical harnessing of electricity to create various thermal tissue effects during clinical applications requiring resection, incision, hemostasis, and devitalization of target tissue. Electrocautery is often used interchangeably with electrosurgery but is a misnomer since it merely represents the ability to “burn” (coagulate) with electricity and not cut or perform a combination of both cutting and coagulation tissue effects.

Electrosurgery was introduced in Europe in 1923 by Erbe Elektromedizin GmbH and in 1926 (Figure 12.1) in the United States by William Bovie and Harvey Cushing (Figure 12.2) [1]. Grant Ward, a well‐known surgeon of his time, recognized early in 1932 how dangerous electrosurgery could be when used by an untrained individual. He stated: “An adequate surgical training is a prerequisite to the adoption of electrosurgery…. It little behooves the novice to take up such a powerful weapon—dangerous in the hands of the unskilled” [2]. The surgeon JL Glover wrote about the use of thermal knives compared with other modalities in 1978, shortly after the arrival of modern isolated generators. He opined: “There is no group of instruments in the surgical armamentarium that is used as frequently and understood as poorly as electrosurgery units…” [3]. In the 1960s and 1970s, electrosurgical units (ESUs) were an absolute mainstay in medical care, but few among medical professionals had formal education regarding their use. The Journal of the Association of Operating Room Nurses, the Journal of the American Medical Association, and the American Journal of Surgery and Cancer all carried articles in the late 1960s and 1970s about injuries to patients from electrosurgery.

Before the newer “isolated system” safety features were developed in electrosurgery in the late 1960s, there were some catastrophic injuries surrounding the use of electrosurgery. The alternate site burn was usually caused by electrical energy taking the path of least resistance via an EKG electrode. This burn could be deep, even charring tissue down to bone. Another example was the return plate site burn resulting from the consequences of turning up power without first checking the status of the patient plate. It could have been incorrectly placed over a bony prominence, incorrectly oriented for the procedure being performed, be dehydrated when applied, or not adherent well to the skin. Electrosurgery was developing a “bad name,” but these were all preventable errors. While burns cannot ever be totally eliminated when using ESUs, the current “isolated systems” work with safety systems in the generator to help prevent injuries such as these.

Multiple elements contribute to the skill of the art and science of using electrosurgery as depicted in Figure 12.3. Successful training in the use of electrosurgery therefore requires understanding of:

  1. The basics of electricity
  2. The difference between monopolar and bipolar devices
  3. Safety measures in electrosurgery
  4. Tissue effects of electrosurgery in endoscopy
  5. Clinical applications of electrosurgery in endoscopy.

Basics of electricity as applied to electrosurgery

There are some basic rules regarding all electrical circuits, which also apply to clinical use:

  1. Electricity always takes the path of least resistance.
  2. Electricity always seeks ground.
  3. There must be a complete circuit for electricity to flow.

Basic terminology is important since generators vary and the user must understand how to adjust their controls in order to achieve the desired clinical effect safely: Current is the flow of electrons and is measured in amperes or amps. Resistance or impedance represents the obstacle to the flow of current and is measured in ohms. Voltage is the driving force pushing current through the resistance and is measured in volts. Energy is a basic universal concept in physics and applies to many systems where forces are applied or transferred and is measured in joules. Power is the rate of transfer of energy and is measured in watts. One watt is a rate of one joule per second. Frequency is the rate at which the electromagnetic wave (such as an alternating electric current) changes direction and is measured in hertz (abbreviated to Hz). One hertz is equivalent to one cycle per second.

Photo depicts the Erbostat: the first electrosurgical generator produced by Erbe-Elektromedizin GmbH in 1923.

Figure 12.1 The “Erbostat”: the first electrosurgical generator produced by Erbe‐Elektromedizin GmbH in 1923.

Photo depicts the first Bovie generator designed by Bovie and Cushing in 1926.

Figure 12.2 The first “Bovie” generator designed by Bovie and Cushing in 1926.

The behavior of electricity is governed by the laws of physics and its principles are predictable. Four variables are present in its equations: resistance (R), voltage (V), current (I), and power (P). They are associated through the equations V = I × R and P = V × I. When any one of the variables changes, the others are affected. All three properties are present in an electrical circuit or pathway when used in electrosurgery.

Schematic illustration of the integration of art and science in electrosurgery.

Figure 12.3 The integration of art and science in electrosurgery.

Parts of the human body have electrical characteristics that can be represented by variations in impedance as shown in Figure 12.4. Materials that are good carriers of electrosurgery are “conductors,” meaning that they have a low level of resistance. Materials that have a high level of impedance are called “insulators.” Tissue resistance depends to a large extent on its vascularity and water content. As tissue dries out or is desiccated electrosurgically, its resistance increases greatly, and the current flowing through it decreases if the voltage is kept constant. Blood and the lining of the gastrointestinal tract are good conductors of electrosurgical energy. Muscle, skin, and fat are also conductors but have increasing levels of impedance in that order. Bone has a high level of impedance and plastic is an insulator. Gloves insulate us from the electrosurgical instruments.

Schematic illustration of the spectrum of impedance of human tissue.

Figure 12.4 The spectrum of impedance of human tissue.

Other than electrical differences between different tissues, patients are also different “electrically” from each other. Factors such as age, local and systemic disease processes, body build, air resistance in the electrical pathway, and hydration all play a role. The ESU must overcome these barriers and provide safe thermal tissue effects without unnecessary damage to the tissue being treated or elsewhere.

One of the most common questions about electrosurgery is: “Why can the current from a wall socket kill you, but the energy from an electrosurgical generator plugged into the wall will not?” The answer is frequency. A low‐frequency alternating current of 60 Hz, as used in a domestic electricity supply, will cause nerve stimulation, muscle stimulation, pain, and potentially cardiac arrest since it mimics the frequency at which nerves fire. Much higher frequencies as emitted by an ESU generator operate significantly above body frequency, which allows for delivery of energy without interference with the nervous system. For electrosurgery, electrical current from a wall outlet (60 Hz) is passed run through a transformer, which converts the energy to a high radiofrequency (350,000–3,000,000 Hz).

Schematic illustration of the spectrum of frequencies of electromagnetic waves.

Figure 12.5 The spectrum of frequencies of electromagnetic waves.

This high‐frequency alternating current produces thermal tissue effects, resulting in cutting and/or coagulation without neuromuscular stimulation. Figure 12.5 illustrates the spectrum of electromagnetic waves from household current at 60 Hz through 100,000 Hz or 100 kHz, which is the approximate threshold at which the body stops feeling electrical stimulation. ESUs operate at over three times this frequency between 350 kHz and 3 MHz similar to radio waves, which is why such outputs are often referred to as “radiofrequency” or “RF.” Television waves operate at even higher frequencies usually above 50 MHz.

Monopolar and bipolar circuits

Generators typically deliver thermal effects via two types of circuit—monopolar and bipolar (Figure 12.6a,b). Monopolar modes use the patient’s body to complete the circuit between the generator through the active electrode and the grounding pad or patient plate and back to the generator. The benefit of a monopolar circuit is the ability to achieve high levels of thermal effect from a device as well as versatility in regard to cutting and coagulation. Examples of the monopolar mode in endoscopy are the polypectomy snare, sphincterotome, needle‐knife, and argon plasma coagulation (APC). The bipolar or multipolar mode does not require a grounding pad because the circuit is completed between two points on the active electrode. The thermal effect is localized only to the tissue in direct contact with the target electrode. Two examples of bipolar/multipolar devices used in endoscopic intervention are the Gold Probe™ (Boston Scientific, Marlborough, MA, USA) used for hemostasis and the HALO™ devices (Medtronic, Minneapolis, MN, USA) used for tissue devitalization. The instruments are designed to deliver the power and also return it to the generator using only target tissue as the “circuit.” The advantage of this mode is the precise delivery of intense energy into a small space.

Schematic illustration of (a) Monopolar circuit. (b) Bipolar circuit.

Figure 12.6 (a) Monopolar circuit. (b) Bipolar circuit.

(Reproduced with permission from Erbe USA Inc.)

Safety measures in electrosurgery

The return electrode

In monopolar circuits, the return plate, dispersive pad, grounding pad, or neutral electrode collects the electrosurgical energy from the patient and returns it safely to the generator. The energy is returned through a low current density interface between the skin and the pad (see below for an explanation of current density) so that there is no thermal effect to the patient’s skin. Electricity must complete a circuit, or it will not flow. The grounded ESU is still available from several manufacturers and found usually in the ambulatory endoscopy center or office setting. Occasionally, older units are still found in hospitals, and users must be aware of the differences from modern ESUs and their potential dangers. The electrical energy must be able to return to “ground” (its place of origin). In these older units, the energy flows from the generator to the patient via the active electrode through the patient, exits through the dispersive pad, and returns to the grounded generator. The problem with these generators is that the electricity can also seek an alternative path and result in burns. The guidelines from professional organizations maintain that all removable external metal should be removed in order to minimize the possibility of the circuit being completed through a path of least resistance via, for example, an endoscopy table or IV pole.

Modern ESUs are “isolated” and keep current flow within the contained circuit and through the return pad, but electricity still adheres to the two principles: it seeks ground and follows the path of least resistance. If the circuit is broken, no current will flow at any point within the system. An isolated ESU has a transformer that causes the current to return only to the generator and not use alternate pathways to return to its source. If this is not possible, the generator will shut down. An isolated ESU prevents alternate site burns, but not patient return electrode burns.

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Jul 31, 2022 | Posted by in GASTOINESTINAL SURGERY | Comments Off on Principles of Electrosurgery

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