Electrosurgical generators are devices that produce currents of various waveforms suitable for surgical applications. The earliest electrosurgical generators used a spark gap system to produce a highly damped, high frequency current. Shortly thereafter, valve (vacuum tube) generators, which had the capability of producing smooth, sine wave currents, suitable for cutting of tissue, were introduced. The tube generator has since been replaced by the modern, solid state generator. The spark gap and the solid state generators are the two types in modern usage. Solid state generators produce the coagulation waveform by using transistors and solid state components to produce high voltage bursts of current. Spark gap generators produce damped, high voltage bursts of current by discharge of air-spaced plates. Spark gap systems are incapable of producing undamped, cutting current.
Even though solid state generators are capable of producing peak voltages in excess of 10,000 volts, unlike spark gap units, they usually cannot maintain the same level of power output at high impedance loads, as when working in a fluid environment.
Cutting and coagulating currents are produced from two independent generators contained within the ESU. Contrary to what is popularly understood, blended currents from solid state electrosurgical systems are produced by the cutting current generator, and consist of a simple, damped waveform, much less drastic in modulation than the coagulation current. Earlier models, such as combination spark-gap/valve generators, combined the outputs of the cutting generator and the coagulation generator to produce a blended waveform with a much higher root mean square power. In either case, the desired effect is to enable the standard electrode to cleanly divide tissue, while causing sufficient thermal effect to produce hemostasis.