Please enter your terms or keywords to search for.
Electrosurgery Explained – Mechanisms of Electrosurgical Tissue Effects
Electrosurgery Explained – Mechanisms of Electrosurgical Tissue Effects
26 Feb 20265 min read
In the fourth article of the Electrosurgery Explained series, Rich Hoodless discusses the fundamental mechanisms behind electrosurgical tissue effects and how RF energy interacts with biological tissue under different operating conditions.
Extensive research has been conducted to understand the effects of electrosurgical energy at both micro- and macroscopic scales. While a complete understanding involves complex electrical, chemical, mechanical, and thermal interactions, it is valuable to develop a high-level appreciation of how each electrosurgical mode produces its clinical effect.
Before examining individual tissue effects, it is important to distinguish between the two primary electrosurgical operating environments.
Dry-Field Environment
In a dry-field configuration, the electrosurgical device is not substantially immersed in an electrolytic medium such as saline. Current passes from the active electrode through the tissue and returns via a return electrode.
Although small amounts of conductive fluid (e.g., blood or irrigant used for site clearing) may be present, neither the tissue nor the device is surrounded by pressurized liquid.
Examples of dry-field devices include electrosurgical scalpels, forceps, and vessel sealers.
Dry-field vessel sealer illustrating current passing directly through tissue without substantial immersion in saline.
Wet-Field Environment
In contrast, in a wet-field configuration, both the tissue and the device are immersed in saline, typically under controlled flow and pressure conditions.
As in dry-field systems, current passes from the active electrode through tissue and returns to the generator. However, in wet-field applications, the conductive electrolyte between the device and tissue plays an active role in completing the electrical circuit.
Devices operating in wet-field environments include arthroscopic electrosurgical wands and urology or gynecology resection loops.
Wet-field resection loop operating in saline, where the conductive electrolyte contributes to circuit completion.
Mechanisms of RF Electrosurgical Tissue Effects
Coagulation
The primary purpose of coagulation is hemostasis. Secondary effects may include controlled tissue shrinkage for specific clinical objectives.
Coagulation occurs through Joule (resistive) heating. As current passes through tissue, impedance generates heat, raising tissue temperature. The temperature rise must be carefully controlled to avoid boiling or unintended ablation.
Protein denaturation leads to:
- Formation of a coagulum that blocks open vessels
- Shrinkage of vessel walls, further restricting bleeding
Power density in coagulation mode is lower than in cut mode to prevent unintended incision. In wet-field bipolar systems, coagulation plays a critical role in maintaining surgical visibility and preventing “red-outs.”
Cut / Ablation
In cut or ablation mode, RF energy raises tissue temperature sufficiently to vaporize intracellular fluid.
The affected material may include:
- Tissue (vessels, ligaments, skin)
- Conductive fluids (saline, blood)
Each material exhibits different impedance characteristics, which also change dynamically as tissue heats or dehydrates. Generator impedance response technology can dynamically adjust output parameters to maintain consistent cutting performance.
Although cut mode provides a secondary hemostatic effect, excessive thermal spread must be avoided to prevent unwanted necrosis. Proper control of:
- Power levels
- Impedance feedback
- Electrode geometry
- Load curve matching
is essential to achieving a clean, controllable incision without tissue charring.
Dry-Field Cutting
In dry-field cutting, the electrode is brought into direct contact with tissue, completing the electrical circuit.
Even in this configuration, small volumes of conductive fluid may introduce multiple impedance elements in series.
Electrode geometry significantly influences performance. A smaller active electrode increases current density at the tip, producing highly localized tissue heating and therefore precise cutting.
Dry-field electrosurgical cutting occurring at the region of highest current density.
Wet-Field Ablation
In wet-field ablation, the surrounding conductive medium becomes a critical factor.
During activation:
- Local tissue temperature rises
- A vapor pocket forms around the active electrode
- The generator responds to increased impedance by increasing voltage
- Dielectric breakdown occurs
- Plasma forms within the vapor pocket
Excited ions in the plasma disrupt intermolecular bonds, resulting in controlled tissue ablation.
Still images from high-speed video capture (5000fps) of a wet-field device activated in saline in pulsed ablation mode. From Left to Right, the vapour pocket can be seen to form, followed by localised and then stable plasma formation. The orange plasma originates from emission from excited sodium ions in the surrounding saline.
Fulguration
Fulguration is a non-contact surface effect.
The electrode is held slightly away from tissue. A high-frequency, high-voltage electric field ionizes a gaseous medium (typically air). Once ionized, current passes through the plasma arc to the tissue surface without direct electrode contact.
This technique is commonly used for:
- Surface hemostasis
- Lesion treatment
- Tissue drying
Because plasma arcs may branch, the effect is often referred to as spray coagulation.
Simplified diagram showing a monopolar fulguration setup with non-contact plasma arc formation.
Argon Plasma Coagulation (APC)
A related technique, Argon Plasma Coagulation (APC), uses inert argon gas as the ionization medium.
Argon provides:
- A non-combustible environment
- Chemically inert plasma formation
- Greater control over plasma propagation
APC is widely used in gastroscopic and bronchoscopic applications.
Bench test images of a monopolar APC device showing axially and circumferentially firing probes. The purple coloration is characteristic of ionized argon emission.
Engineering Control of Tissue Effects
Understanding these mechanisms is essential for designing electrosurgical systems capable of delivering predictable, controlled clinical outcomes.
ATL has extensive experience developing devices and systems capable of supporting multiple tissue effects—including combinations of coagulation, cutting, ablation, and plasma-based techniques.
OEMs engaging with ATL’s engineering team can leverage decades of experience in:
- Impedance-responsive generator design
- Electrode geometry optimization
- Thermal margin control
- Plasma system development
Nearly 30 years after the founding innovations in Cardiff, the engineering team continues to advance the performance of RF electrosurgical systems in the spirit of ongoing technical refinement.
Frequently Asked Questions (FAQ)
What is the difference between dry-field and wet-field electrosurgery?
In dry-field electrosurgery, the device operates without substantial immersion in saline, and current passes directly through tissue to a return electrode. In wet-field electrosurgery, both the tissue and device are immersed in saline, and the conductive electrolyte plays an active role in completing the circuit.
How does RF electrosurgery coagulate tissue?
Coagulation occurs through resistive (Joule) heating. As RF current passes through tissue, impedance generates heat, leading to protein denaturation, vessel shrinkage, and formation of a coagulum that achieves hemostasis.
What causes plasma formation in wet-field ablation?
During activation, tissue heating creates a vapor pocket around the electrode. As impedance rises, the generator increases voltage until dielectric breakdown occurs, forming plasma. The plasma’s excited ions disrupt molecular bonds, resulting in controlled tissue ablation.
Why is electrode geometry important in cutting mode?
Smaller active electrodes increase current density at the tip, producing highly localized heating. This enables precise cutting while minimizing unintended thermal spread.
What is the difference between fulguration and argon plasma coagulation (APC)?
Fulguration uses ionized air to create a non-contact plasma arc for superficial tissue treatment. Argon plasma coagulation (APC) uses inert argon gas as the ionization medium, providing greater control and a non-combustible plasma environment.