It refers to the path therapeutic current takes from the active electrode back to the unit. In an isolated output unit the path is from the active electrode, through the body, through the dispersive electrode and back to the unit. A very small clinically negligible amount of therapeutic current can stray off to electrical earth ground. The limitation of stray, or “RF leakage” current, prevents alternate site burns and makes isolated output units safe for concurrent use with physio-monitoring equipment and significantly reduces radio interference with other equipment in the room. This has been the standard in general surgery operating rooms for 25 years. Isolated output units absolutely will not work without a dispersive plate in monopolar application.
Therapeutic current in “ground referenced” units returns to the unit primarily through the dispersive electrode, which is connected to electrical earth ground through a capacitor inside the unit. However, therapeutic current will flow through any electrical path to earth ground wherever it is available : capacitively through the chair, through physio-monitoring leads such as EKG leads, or wherever else the patient contacts earth ground. These units can work without a dispersive plate when sufficient capacitive coupling between the patient and the chair exists. These units do interfere with other equipment readily and are not recommended for use in conjunction with physio-monitors or with bipolar accessories. It is also not advisable to touch the metal casing of these units during operation either, since there is a risk of an unpleasant tingling or “shocking” sensation, even a small risk of coagulation burn.