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ssss1 Tissue effect in relation to temperature.

Source: Modified from Dubiel et al. [1].

Temperature (°C) Tissue effect 250 Tissue carbonized from dehydration 100 Cell wall rupture 90 Tissue desiccation 70 Protein denaturing 50 Enzymatic activity inactivated 40 Inflammation and edema

Another important concept in understanding electrosurgery is the concept of power. Power is a measure of work per unit time. It is a function of voltage and current and is measured in watts. Power tells you the rate at which the energy works. Power rises exponentially with increases in voltage and decreases inversely with increases in resistance or impedance. However, voltage is the main determinant of tissue effect and is a function of the waveform that the generator delivers (see waveform section below).

An ESU is composed of four basic components: A generator, an active electrode, the patient, and the return electrode. The ESU uses low‐frequency alternating current (AC) from a wall outlet and converts it to a higher voltage radiofrequency (RF) output. The current can be used to induce diathermy but also stimulates muscle and nerve cells. Stimulation of muscle and nerve cells can lead to pain, muscle spasm, and even cardiac arrest. The sensitivity of nerves and muscles cells to electrical stimulation decreases and the excitability threshold increases with increasing frequency, meaning that nerve and muscle cell stimulation is refractory to electrical stimulation above 100‐kHz [2]. Therefore, electrosurgical devices use frequencies in the range of 350–500 kHz. This range is referred to as the medium RF electromagnetic spectrum (ssss1).