Introduction

The term electrosurgery (radiofrequency surgery) refers to the passage of a high-frequency (radiofrequency) electrical current through the tissue in order to achieve a specific surgical effect such as cutting or coagulation. Each electrosurgical device consists of a high frequency electrical generator and two electrodes (Figure 1). Adjacent to the active electrode, tissue resistance to the passage of alternating current converts electrical energy to heat, resulting in thermal tissue damage.^1,2 The large return electrode disperses the current, reducing the current density to levels where tissue heating is minimal.

Figure 1. An electrosurgery circuit in monopolar biterminal mode  (image from Taheri A et al. Electrosurgery; basics and principles. Journal of American Academy of Dermatology. In press.)

Basic mechanism of electrosurgery

Electrocoagulation occurs when tissue is heated below the boiling point and undergoes thermal denaturation.³ A slow further increase in temperature leads to vaporization of the water content in the coagulated tissue and tissue desiccation. As more superficial coagulated tissues dry out, they become less electrically conductive leading to spark formation through desiccated tissue. Desiccation is not a method or a distinctive final result; it is only the final stage of coagulation that may or may not happen.

A sudden increase in tissue temperature above boiling point results in rapid explosive vaporization of the water content in the tissue adjacent to the electrode. This leads to tissue fragmentation and cutting (electrosection).^4-6

Current waveforms

Electrosurgical generators are able to produce a variety of electric waveforms (Figure 2). The name of each electrosurgical waveform or mode does not necessarily translate to the final tissue effect. The only variable that determines effects of a current is the depth and the rate at which heat is produced. The wave-form, voltage and power of electrosurgical current and the size of electrode tip can affect the depth and the rate of heat production and indirectly influence the final effect on the tissue.^3,7,8

Figure 2. Cutting mode uses a continuous waveform which is able to provide the maximum output power of the generator. Other modes use intermittent waveforms with lower maximum power than cutting waveform. An intermittent waveform incorporates higher voltage than a cut waveform at the same power setting  (image from Taheri A et al. Electrosurgery; basics and principles. Journal of American Academy of Dermatology. In press.)

Electrosurgical modalities

Electrocoagulation

Electrocoagulation can be performed in contact mode or in spray (fulguration) mode. However, the term electrocoagulation is usually used to refer to electrocoagulation in contact mode.

For superficial coagulation of small areas a fine-tip electrode is used to concentrate a low power current to a fine point (Table 1). The current density in tissue rapidly decreases with distance from the electrode (Figure 3); therefore, heat generation is practically confined to the vicinity of the electrode tip on the surface.⁹

When using a large-tip electrode with a large electrode-tissue contact surface, a higher power output should be used (Figure 3).¹⁰ Current density decreases with distance from the electrode surface more slowly compared to a fine electrode. A higher power output and slower decrease in current density leads to deeper tissue injury. A large electrode tip, therefore, should be used only for deep coagulation (Table 1).¹¹

In electrofulguration, the active electrode is held above the tissue. Using an interrupted high-peaked-voltage output, an electric discharge arc (spark) forms that rapidly dances from one location to the other and spreads the current over an area larger than the tip of the electrode.¹² Each spark carries the current to a very small point, acting as a very fine electrode. Given a relatively low power, tissue destruction and coagulation appears within a thin superficial layer of tissue. However, if electrode is kept over a confined area, continuous heat production on the superficial layers can cause heating of deeper layers and a deep coagulation (Table 1).

Figure 3. Electrocoagulation (image from Taheri A et al. Electrosurgery; basics and principles. Journal of American Academy of Dermatology. In press.)

Electrosection

The major advantage of electrosection over scalpel is that hemostasis is achieved immediately upon incision by coagulation on either side of the incision wall.

A thin needle can concentrate current on a small area and allows the same cutting effect to be achieved with a lower power setting. This leads to less heat production and less collateral tissue coagulation compared with a thicker electrode.^6,13 Therefore, a thin needle is used to make a relatively clean incision with minimal coagulation and hemostasis on the incision walls (Figure 4). A thick needle electrode can cut through the tissue using a very high power current. Current density and temperature decreases from electrode more slowly compared with a thin electrode and results in a deeper coagulation margin (blend cut; Figure 4).

When the cutting electrode comes in contact with the tissue, an initial tissue heating and explosive vaporization of the water around the electrode leads to isolation of the electrode from the tissue. The current then passes through the vapor cavity by spark without a direct contact between the active electrode and tissue.^4,9 The higher the peak voltage of the current, the larger the sparks. Larger sparks spread current to a wider area of tissue around the electrode and act as if a thicker electrode is being used.¹⁴ Therefore, an interrupted high-peak-voltage current provides a blend cut (Figure 4).^3,15

In order to have less collateral tissue damage and coagulation on the incision walls, contact time should be reduced to minimize heat production and conduction.¹⁶ Therefore, the cutting of the tissue should be brisk with the lowest effective power setting.^5,6

Figure 4. Electrosection. Left: A thin needle is able to concentrate a low-peaked-voltage, low-power current (cutting current with relatively low power). Middle: A thick electrode provides deeper coagulation margins. Right: A high-peaked voltage current (blend or coagulation waveforms) produces large sparks that cannot concentrate the current  (image from Taheri A et al. Electrosurgery; basics and principles. Journal of American Academy of Dermatology. In press.)

Bipolar versus monopolar electrosurgery

In electrosurgery, the prefix 'mono-' and 'bi-' polar refers to the number of active electrodes. In monopolar electrosurgery an active electrode carries current to the tissue (Figure 1). Current then spreads through the body to be collected by a dispersive electrode. In bipolar electrosurgery, however, the current passes only through the tissue between the tips of a bipolar forceps (Figure 5). A bipolar forceps acts as two active electrodes.^17,18

Figure 5. Bipolar electrosurgery circuit  (image from Taheri A et al. Electrosurgery; basics and principles. Journal of American Academy of Dermatology. In press.)

Biterminal versus monoterminal electrosurgery

The prefix 'mono-' and 'bi-' terminal refers to the number of electrodes that are in contact with patient's body (Figure 1 and Figure 6).

In so-called 'earth-referenced' electrosurgical units, the return electrode is connected to earth and therefore, the earth and all conductive objects around the patient's body can act as a capacitive-type dispersive electrode (Figure 6). Electrosurgery can be performed using these units regardless of whether a dispersive electrode is attached to the patient. Performing monopolar electrosurgery without using a dispersive electrode is called monoterminal electrosurgery (Figure 6).

During monoterminal electrosurgery with an earth-referenced unit, if an electrically conductive object such as a metal table or surgical staff comes into contact with the patient's body, current concentration at this point may result in a burn. For this reason, monoterminal mode is used only on conscious patients who would be aware of such complications.

The type of electrosurgical unit commonly used in operating rooms today is floating or isolatedwith the dispersive electrode isolated from earth. An isolated generator will not work unless the dispersive electrode is attached to the patient.⁷ During activation, if the patient's body comes in contact with an environmental object, the risk of a burn is low.

Although a good dispersive electrode reduces the risk of distant site burns, inadequate contact of the dispersive electrode with the patient's body may result in a smaller contact area and current concentration at this point may lead to a burn at this site.^3,7,19,20

Figure 6. Monoterminal electrosurgery using an earth-referenced unit. The return electrode is connected to the earth  (image from Taheri A et al. Electrosurgery; basics and principles. Journal of American Academy of Dermatology. In press.)

Electrosection versus scalpel surgery

Electrosection is used as an alternative to scalpel surgery. While many studies support better outcomes using scalpel surgery, there is also literature favoring electrosection.^21-24 A general concept is to avoid electrosection for cutting skin when a primary closure is planned.

Electrosection results in some histologic distortion of surgical margins. For specimens requiring histopathological analysis, scalpel surgery is preferred.

Electrosurgery versus CO₂ laser surgery

Coagulation of tissues such as warts or skin tumors can be achieved using electrosurgery or CO₂ lasers. Both methods can provide superficial destruction, however electrocoagulation can be used more easily for deeper tissue destructions. While a CO₂ laser is more predictable and controllable for superficial destructions, in experienced hands, electrosurgery has more flexibility for choosing the depth of injury.

Similar to electrosection, CO₂ lasers can provide coagulation of the incision walls and hemostasis. Both techniques are operator dependent and cannot be standardized. Therefore, comparing these modalities in clinical settings is not easy. Some studies show more collateral coagulation using electrosection, while others report the opposite results.^23-31

Conclusion

Superficial coagulation of small areas can be performed with a fine-tip electrode. A large-tip electrode is used for deep coagulation. Making a relatively clean incision with little hemostasis (pure cutting) needs a thin electrode and a cutting current (cut mode). Blend cutting can be performed using an interrupted current (blend or coagulation mode).

In regards to safety, monoterminal mode may be limited, especially when using a high power on an unconscious patient. 

Table 1. Settings of an electrosurgical unit for destuction/coagulation of different skin targets

References 

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