Electrosurgery Explained: Pole to Pole — Electrode Configurations in Electrosurgical Systems

Monopolar Electrosurgical Systems

Modern monopolar systems employ an active electrode, typically located at the distal end of the instrument. Electrical energy supplied by the electrosurgical generator is delivered through this active tip to the operative site. Current then returns through the patient’s body via a relatively large dispersive (return) pad placed in intimate contact with the patient’s skin, completing the circuit back to the generator.

Because the active electrode has a much smaller surface area than the dispersive pad, current density is significantly higher at the instrument tip. This concentration results in a localised tissue effect at the distal end of the instrument rather than at the return pad.

Monopolar systems can offer greater haemostatic capability compared to bipolar systems, as the return path through the patient enables deeper coagulative effects. To mitigate risks associated with the dispersive pad, such as pad-site burns, monopolar systems typically incorporate contact-quality monitoring to ensure adequate pad-to-skin contact is maintained throughout the procedure.

The development of monopolar electrosurgical systems was closely tied to early advances in high-frequency current delivery and waveform control, explored in the first article of the Electrosurgery Explained series.

From an engineering perspective, monopolar instruments are generally simpler in construction, as only a single electrode is present within the applied part.

Bipolar Electrosurgical Systems

In bipolar systems, both the active and return electrodes are located on the instrument itself. Electrical current flows from the active electrode—sometimes via a conductive medium such as saline—into the target tissue and returns locally through the adjacent return electrode back to the generator.

Because the electrodes are in close proximity, they must be separated by robust dielectric insulation. High-performance ceramic or polymeric insulating materials are often required to maintain electrical integrity under high-frequency operating conditions.

The relative geometry and spacing of the active and return electrodes can be adjusted to precisely control the distribution of the coagulative effect or ablative plasma, depending on the desired tissue interaction. Careful design is required to minimise effects such as return-fire, where plasma formation becomes biased toward the return electrode when the device is embedded in tissue.

By confining the current path to the immediate treatment area, bipolar systems eliminate the need for a patient return pad and remove the associated pad-site burn risk.

Tripolar Electrosurgical Configurations

In the bipolar configurations described above, both cutting/ablation and coagulation functions typically share a common return electrode. To optimise performance across these distinct functions, additional return electrodes can be incorporated into the instrument, allowing current paths to be selectively modified based on the intended tissue effect and clinical use.

This tripolar approach enables separate optimisation of ablation and coagulation modes by tailoring current flow for each function. Tripolar technology developed at ATL’s Cardiff site can be leveraged by OEMs seeking further refinements in RF ablation and coagulation performance.

Selecting the Right Electrode Configuration

Each electrode configuration—monopolar, bipolar, and tripolar—offers distinct advantages and trade-offs in tissue effects, safety profile, and device complexity. OEMs engaging with ATL can leverage ATL's expertise across all electrosurgical electrode configurations to develop systems aligned with specific clinical requirements and performance goals.

In the next article of the Electrosurgery Explained series, the underlying mechanisms of electrosurgical energy delivery and their effects on tissue will be discussed.