What is electrosurgery?
Electrosurgical generators are capable of producing a variety of current waveforms. Depending on the clinical results desired, different waveforms can be used to produce differing tissue effects. An understanding of the ways in which the electrosurgical generator can modify current is necessary to better understand the options available to the surgeon.
Any current can be classified as either direct current or alternating (varying) current. Direct current is constant, never changing in direction (polarity) or magnitude. Direct current is the type produced by batteries. It is not used in electrosurgery because of its tendency to produce depolarization of neural and muscular tissue.
Alternating current is so named because its direction (polarity) changes (alternates). This type of current is similar to that which comes from electrical wall outlets. The rapidity with which the direction of current flow changes per unit of time is referred to as frequency, and is measured in Hertz (Hz). One complete cycle per second is one Hz. If a current alters polarity one million times per second, it is a one megahertz (MHz) current. Electrosurgical generators typically operate at frequencies between 400,000 Hz and 2.5 MHz, although some generators produce currents with frequencies as high as 3.5 MHz. Because these frequencies fall in the range of radio waves, electrosurgical generators are sometimes called radio frequency generators, and do, in fact, produce radio waves as a byproduct. Either excessively high or low frequencies can cause undesirable effects. Depolarization of susceptible tissues ceases at frequencies above 10,000 Hz. Excessively high frequencies tend to encourage current leakage.
Waveforms can be altered by the multiplication of two or more signals, a process called modulation. Damped and blended currents are examples of this process. There are three basic types of current waveforms used in electrosurgery: cutting current, coagulation current, and blended current.