Electrosurgery

Definition

Modern electrosurgery encompasses a group of techniques by which high-frequency alternating electrical current is applied to living tissues in order to achieve superficial coagulation, deep coagulation, or cutting of the skin. Since living tissue is a poor conductor of electricity, the flow of electrical current is hampered and builds up at the site of application. This resistance to the flow of electricity results in its conversion to heat. The use of different varieties of electrosurgical current, each characterized by a distinctive waveform, results in unique biologic outcomes, including desiccation, coagulation or section of treated skin.

Electrocautery

The forerunner of modern electrosurgery was electrocautery (from Greek kauterion , branding iron) . In electrocautery, invented in 1875, a metal wire is heated by resistance to the flow of direct current electricity, as in an electric toaster. Hemostasis (even in a wet field) can be obtained with electrocautery, but the resulting third-degree burn may result in prolonged healing times and may cause inferior cosmetic outcomes.

Of note, electrocautery, with its hot element ( Fig. 140.1 ), is different from modern electrosurgery, in which high-frequency alternating current is applied via an unheated electrode. Electrocautery units are of value for providing hemostasis for surgical patients with pacemakers and implantable cardioverter-defibrillators (ICDs), because external electromagnetic fields may compromise the function of these devices. A number of electrocautery units are currently produced; among them is the Thermal Cautery Unit (Geiger Medical Technologies Inc.). Disposable battery-powered electrocautery instruments are also available, but the desired temperature can diminish during contact with tissue.

Historical Aspects

Although used by most dermatologists on a daily basis, high-frequency electrosurgery (often referred to as “radiosurgery”) could not have been developed if several major advances in the knowledge of electricity had not occurred. In order for alternating current electricity to be utilized for medical purposes, it was necessary for high-frequency currents to be produced. A generator that could provide such current was developed in 1889 by Thompson, who noted heat in his wrists when current was passed through his hands when immersed in saline solution . Experiments conducted by Jacques Arsène d’Arsonval in 1891 established that the application, in human subjects, of electric currents with frequencies greater than 10 000 cycles per second (10 KHz) failed to cause neuromuscular stimulation and the associated tetanic response . Also in the 1890s, Oudin, following some modifications to d’Arsonval's equipment, was able to generate a spray of sparks that caused superficial tissue destruction.

At the turn of the twentieth century, Rivière conceived the notion of using very small treatment electrodes in order to concentrate the current density. This would enable one to treat a skin lesion with an electric spark . Walter de Keating-Hart and Pozzi in 1907 introduced the term “fulguration” (from Latin fulgur , lightning), referring to the superficial carbonization that resulted when the spark from the Oudin coil was used to treat skin. They claimed that this modality was ideal for treating skin cancer and that the spark could selectively destroy tumor cells by interfering with their source of nutrition.

In 1909, Doyen introduced the term “electrocoagulation” (from Latin coagulare , to curdle) to describe a different form of electrosurgery in which tissue was touched directly with the treatment electrode and an indifferent electrode was added to the circuit. The indifferent electrode allowed for direct removal of the electricity entering the patient and caused the latter to flow back into the electrosurgical device. By removing this static energy build-up, shocks were avoided in surgeons and other bystanders. The amperage was effectively increased while the “recycling” of electrical current allowed for lower voltages to be utilized. The current produced with this biterminal arrangement penetrated more deeply than fulguration and directly coagulated tissues rather than causing only surface carbonization. Doyen claimed that this more deeply penetrating current was more likely to be effective in the destruction of tumor cells.

William Clark, in 1911, reported on the use of an electrosurgical output that caused dehydration of tissue without carbonization at the surface . He substituted a multiple spark gap for the usual single one in a monoterminal Oudin current generator. This provided a smoother current that resulted in the production of fine sparks as opposed to the long, thick sparks seen with electrofulguration. Clark used the term “desiccation” (from Latin desiccare , to dry out) to describe this action.

The next major event in the development of electrosurgery came in 1923 when Dr George A Wyeth, a noted tumor surgeon, used electrosurgery for cutting tissues . His apparatus, which he termed an “endotherm knife” (Greek endo , within; thermē , heat), used a thermionic vacuum tube instead of a spark gap . Wyeth called the technique “electrothermic endothermy”. He believed that the technique was particularly applicable to tumor surgery since it sealed off not only the smaller blood vessels but also the lymphatics that might otherwise provide for dissemination of metastatic disease.

A Harvard physicist, William Bovie PhD, probably made the most important contribution to the development of electrosurgery. With financial assistance from the Liebel-Flarsheim Company of Cincinnati, he built an operating room electrosurgical device that offered both coagulation and cutting currents . Dr Harvey Cushing, a distinguished neurosurgeon, became quite interested in these techniques and, with Bovie at the controls, began using electrosurgery for controlling bleeding and cutting through tissues during surgical procedures at Peter Bent Brigham Hospital in 1926. Dr Cushing's favorable impressions of electrosurgery assured acceptance of this technique by the surgical world. The subsequent impact of Bovie's machine upon medicine was so great that the word “bovie” is still often used generically as a noun to refer to an electrosurgical apparatus or even as a verb to describe the act of performing electrosurgery .

Electrosurgical Devices and Outputs

The circuitries of all electrosurgical instruments share certain design features necessary for production of suitable electrical outputs for electrosurgery. Standard household current first passes through a transformer which alters the voltage, providing the levels and characteristics required for the instrument's various circuit functions. The current next travels through an oscillating circuit that may employ a spark gap, a thermionic vacuum tube, or solid state transistors to increase electrical frequency. Finally, this altered electrical energy is delivered to the treatment electrode.

Each electrosurgical current produces its own unique wavy pattern of current flow, or waveform . The latter may be either damped or undamped , depending on the type of oscillating circuit used. In general, damped waveforms provide electrodesiccation and electrofulguration, whereas the application of moderately damped and undamped currents results in electrocoagulation and cutting currents, respectively ( Fig. 140.2 ). The spark gap generator produces a damped wave, consisting of bursts of energy in which successive wave amplitudes gradually return to zero. This occurs due to the resistance to energy flow presented by the gap.

Use of a thermionic tube results in a more uniform output. The valve tube circuit is able to neutralize the internal resistance responsible for the damping effect seen in the spark gap circuit, and the amplitude of output therefore remains unchanged. Depending on the circuitry used, the output can be moderately damped (partially rectified) or slightly damped (fully rectified). A filtered, fully rectified output is essentially continuous and uniform, similar to an undamped wave. The different types of waveforms each result in different biologic outcomes and are, therefore, used for different electrosurgical procedures .

Terminology: Monopolar, Bipolar, Monoterminal and Biterminal

The terms monopolar and bipolar denote the number of tissue contacting tips at the end of the surgical electrode. When the surgical electrode has only one tip projecting from its end, it is a monopolar electrode. If it has two tips, it is a bipolar electrode. Therefore, an electrosurgical forceps (that plugs into two ports on the electrosurgical device) is considered to be bipolar, as opposed to a pointed electrode, which is monopolar (and plugs into one port on the device).

Monoterminal refers to the use of a treatment electrode without an indifferent or dispersive electrode (“ground plate”). Biterminal denotes that both treatment and indifferent electrodes are used (see Fig. 140.1 ). Such is the case with electrocoagulation and electrosection, in which use of the indifferent plate, although not technically necessary for the machine to work, will definitely enhance the efficiency of the electrosurgical apparatus. In biterminal electrosurgical applications, there is “recycling” of the energy that comes out of the treatment electrode, passes through the patient and is then removed from the patient via the indifferent electrode. Electrodesiccation and its variant, electrofulguration, are monoterminal procedures in which the indifferent electrode serves no purpose and, in most instances, is not even connected to the patient.

A simple way to visualize this is to think of the wires coming out of the machine as terminals. If only one wire (the handpiece for the electrode) is attached to the machine, then the application is monoterminal in nature. If, in addition, a “ground plate” is used, requiring a second wire to be attached to the machine, then the procedure is biterminal (see Fig. 140.6 ).

When a ball electrode is used to electrocoagulate a bleeding vessel, one is using biterminal, monopolar electrosurgery. In the case of bipolar forceps in which the electrode is connected to both the active and the dispersive electrode termini, we are using a biterminal, bipolar modality.