By means of two electrical connections called “electrodes”.
In “monopolar” electrosurgery, one is an “active” electrode and is used to introduce therapeutic current into tissue. These are also called “tips” or “electrode tips” and come in a wide variety of sizes and shapes suited to specific clinical indications for incision, excision, curettage, and coagulation. These are held in an insulated hand piece. The other electrode is the “dispersive” electrode and is in the form of a large flexible pad. “Dispersive” connection to the patient is by means of capacitive coupling which works through normal street clothing without direct skin contact so that the patient reclines against the dispersive pad ( or “plate” ) completing the electrical circuit.
The “active” electrode is many orders of magnitude smaller in surface area that the “dispersive” electrode so that therapeutic current is highly concentrated in the area being treated. In contrast, therapeutic current is distributed over the very large area of the “dispersive” pad such that current density at any point is too low to induce any measurable histological effect, hence the term “dispersive”.
In “bipolar” electrosurgery, both electrodes are the same or similar size and are mounted on a common hand piece. No separate dispersive plate or pad is used and the cable from the bipolar hand piece to the electrosurgery unit has two conductors.