Frequency
Several considerations place limits upon the frequencies at which electrosurgical generators can operate.
Frequencies in excess of 10,000 Hz are necessary to produce the diathermic effect without neuromuscular stimulation. Frequencies below this threshold cause undesirable depolarization of susceptible tissues (heart, muscle, and nervous tissue), leading to tonic and clonic muscle contractions with rhabdomyolysis and cardiac dysrythmias.
Similarly, the use of excessively high frequencies can lead to surgical complications. The primary concern in the design of electrosurgical equipment is the containment of the current pathway within its intended circuit. Travel of the current via alternate, undesired pathways can produce electrosurgical burns. Such an alternate pathway may occur via a pathway of less capacitive resistance to ground. Capacitance, technically defined as leakage or loss of current through an insulator, occurs with much greater efficiency as the frequency of the current increases, allowing shunting of current to occur (short circuit). Capacitive coupling can occur if other electrical circuits, such as monitoring equipment, are in contact with the patient, causing alternate site burns.
It is for these reasons that almost all contemporary electrosurgery generators use a frequency of between 400,000 Hz and 2.2 MHz, with the most commonly used generators producing either 600,000 Hz or 750,000 Hz.