Steven Walsh, Ph.D. Unique energy-based surgical devices afford broad clinical use in the cutting, coagulation, and ablation of tissues using a high velocity jet of thermal plasma, and the PlasmaJet surgical system is one example of this medical device evolution. Plasma is formed when sufficient energy is added to remove outer electrons from a gas to form ions. Often called the fourth state of matter, after solid, liquid, and gas, plasmas are a highly energetic gaseous phase consisting of a balance of molecular or atomic ions and free electrons. Plasmas are naturally occurring and represent the most abundant form of matter in the universe; however, it is the artificially generated plasmas that have multiple technical applications principally derived from the energy released when the ionized gas transitions from the plasma state back to the gaseous state.

There are two general categories of plasmas—cold and thermal—based on the relative proportion of ionized to non-ionized gas particles. Cold plasmas have a low proportion Nikolay Suslov, Ph.D. (typically less than one percent) of gas particles in the ionized plasma form, whereas thermal plasmas are virtually fully ionized. Although the ionized particles in both classes are extremely energetic, the low proportion in cold plasmas makes this form not macroscopically hot. Cold plasmas are extensively used in industry for critical surface cleaning and have been proposed for multiple medical applications, including sterilization or decontamination processes. Thermal plasmas are characterized as being macroscopically hot and have widespread industrial use in materials cutting.

The PlasmaJet surgical system employs this latter form of thermal plasma created by the passage of high purity argon gas across an electrical arc with tightly controlled current and timing parameters. The plasma jet is formed by the rapid volumetric expansion of the gas as it is ionized and contained within the device tip, and exits at a high temperature and high velocity. The characteristics of the jet responsible for cutting, coagulation, or ablation are controlled by the current profile of the arc and the amount of gas flowing across that arc. The plasma jet is then directed to the tissue surface where the plasma interacts with the tissue to produce the desired effect. As a primarily thermally mediated process, the effect on the tissue surface is controlled by the power density of the jet, with coagulation occurring with a relatively diffuse or low power density, and ablation with an increased and more focused power density. Cutting is a highly focused form of ablation, where the ablation occurs rapidly over a narrow surface area.

The benefits of PlasmaJet occurs when the plasma jet impinges on the tissue surface and the high energy ionized particles transfer their energy to the tissue surface as the plasma transitions back to the gas state. Unlike other energy-based surgical devices where thermal energy is conducted through bulk tissue volumes several millimeters deep, the energy transfer with the PlasmaJet occurs at the immediate surface of the tissue to first vaporize the water and create a dry sponge to a depth of only a few hundredths of a millimeter. As the thermal energy is conducted into the depth of the tissue, protein denaturation occurs, resulting in a dense coagulated layer that provides a hemostatic boundary. The balance of thermal energy applied by the plasma jet and the dissipation of that heat into the body results in a greatly reduced volume of tissue affected, often less than a millimeter deep. Tissue ablation or cutting occurs as the dried superficial tissue layer is vaporized and the zone of coagulation propagates from the plasma jet. Since the same principles of heat diffusion hold as with coagulation, the zone of thermal damage in cutting is typically less than three millimeters from the ablated or cut tissue surface.

Recent enhancements to the standard continuous plasma jet have been developed to improve the use characteristics of PlasmaJet by creating a plasma flow with a volumetrically oscillating jet. Termed “Ultra,” the oscillating jet is formed by rapidly modulating the plasma generating arc current between two different amperages to create a train of plasma pulses with alternating high/low temperatures and corresponding high/low velocities. Under the low current phase of the cycle, the plasma jet formed is at a lower temperature and lower velocity than the jet created during the high current phase. The trailing high velocity high current pulse thus impacts the low velocity low current pulse causing both axial and radial scattering of the plasma particles. For coagulation and ablation, this scattering results in an expansion of the jet volume and an increased zone of effectiveness. The modulation between the high and low current levels also allows higher temperature plasmas to be created (during the high current phase) than would be possible under continuous plasma operation, and thus Ultra also affords improved cutting efficiency.

As a relative newcomer to the world of energy-based surgery, PlasmaJet has tremendous potential to expand across a variety of general and specialty surgical applications, and can be specifically tailored to meet clinician functional needs for tissue cutting, coagulation, and ablation

A review of the current literature shows broad use of plasma surgery in gynecology and oncology, and it is expected to find similar use in spine, thoracic, and neurosurgical applications. Over the coming years, the system will continue to evolve with improved handpiece features to facilitate use in more complicated open and laparoscopic surgical procedures, as well as further developments to the plasma generation platform technology that will allow further improvements in surgical effectiveness.