**6. Plasma background**

Plasma is created when a gas is energized to a level that accelerates and frees electrons, resulting in a mixture of neutral atoms, charged ions and molecules. Plasmas occur in nature, within stars and the polar aurora. Early research on plasmas arose from controlled laboratory conditions and gave rise to applications within Medicine. Today, medical plasmas are in use for a spectrum of applications, including wound debridement, tissue regeneration, reducing cancerous cell proliferation and inducing selective apoptosis of neoplastic cells [19]. Medical plasmas are used in minimally invasive surgery in the fields of Gynecology, Urology, Otolaryngology and Gastrointestinal endoscopy. A well-known example is the Argon plasma technology used for soft tissue coagulation to reduce bleeding and tissue ischemia [20]. As discussed below, the use of a stream of ionized inert gas to deliver radiofrequency energy provides an advantageous alternative energy source for skin and soft tissue contraction.

## **7. Physics and mechanics of Renuvion®**

Renuvion® is a helium-based plasma and radiofrequency technology that has been cleared by the Food and Drug Administration for cutting, coagulation and ablation of soft tissue. It creates a direct discharge, non-equilibrium, low temperature plasma beam at atmospheric pressure as helium gas is passed over a sharp, conductive point held at high voltage and high frequency. The system consists of a RF generator, supply of helium gas and an electrode within the tip of a handpiece [21]. The generator operates at a maximum of 4.0 kV, 40 Watts and 490 kHz frequency [22]. Independently tunable power levels, gas flow rates and pulsing of energy delivered provides a high level of precision. Unlike monopolar and bipolar instruments, the Renuvion® handpiece does not conduct heat after its application.

Renuvion® provides rapid heating of tissue in 360° with minimal depth of treatment. Heat is generated by two methods. The first is the ionization and rapid neutralization of helium atoms as the gas passes over the RF energized electrode. Second, a portion of RF energy used to energize the electrode is carried to the tissue by the plasma stream, whereby the tissue's resistance generates heat [23]. The electrosurgical generator maintains a consistent power output over a range of impedances [10]. In contrast, monopolar and bipolar devices have limited power output in tissues with greater impedance [10]. The mechanical movement of the handpiece and hence, the direction of plasma flow subcutaneously, is tracked by the light spray generated by the plasma streams. In Renuvion®, the colorless, monatomic, inert helium gas stream also delivers kinetic energy to clear the target tissue of fluid or debris [24].

At clinically equivalent settings, Renuvion® offered more control of tissue response with lower lateral and depth of thermal spread compared to monopolar, Argon, CO2 laser [25]. In a porcine model utilizing kidney, muscle, ovarian and uterine tissue blocks, the depth and spread of coagulation were found to be a function of the current density, gas flow rate, duration of application and distance of the probe tip to the target tissue [24]. Increasing the power increased the heat energy delivered to the tissue [24]. Histologic analysis demonstrated 2 mm depth of thermal spread following 5 sec of 100% power and 5 L/min Helium gas flow [24]. The same study demonstrated that prolonged exposure up to 30 seconds did not increase the depth of thermal effect over 3 mm, just the length and width of thermal spread, in all tissue types studied [24]. The depth of collagen denaturation was seen histologically to be 0.180–0.247 mm at both 50% and 100% power. Conductive heat transfer to surrounding tissues offers less heat transfer to the epidermis, thereby eliminating the need for external temperature monitoring.

The inherent resistance (impedance) to the flow of RF current through tissue increases as tissue is treated and desiccates. The RF current will preferentially flow through the path of least resistance characterized by the lowest tissue impedance. As such, the plasma beam alternates between treating different tissues surrounding the device. Continuous movement of the handpiece further introduces new, lower impedance tissue to the tip and delivers uniform energy to a large area. This lowers the need for the user to constantly redirect the handpiece. The RF energized plasma stream preferentially seeks tissue with the lowest impedance, like the fibro-septal network, to receive the majority of energy and undergo coagulation and contraction [26]. The low current of the Renuvion® device further disperses and prevents tissues from being over treated when multiple treatment passes are done. The increase in tissue impedance from coagulation preferentially diverts Renuvion® energy towards adjacent untreated tissue with subsequent passes. Subsequent live swine studies outlined the impact of device settings on the internal and external tissue temperatures with the use of a Forward-Looking Infrared Camera [26]. It was demonstrated that 6 passes of 60–80% power, at 1–4 lpm gas flow, and a handpiece speed of 1 cm/sec, raised internal temperatures to above 85° Celsius for a duration of 0.08 seconds, while external skin temperatures stayed within a safe range of 3.6° of baseline [26]. The internal tissue heating cycle lasted an average of 0.24 seconds from the time in which the handpiece tip approached to raise the target tissue temperatures, passed directly over and then moved past to lead to a rapid return to baseline temperatures. Maximum collagen contraction occurred within 0.044 seconds [2, 26]. The rapid rise to 85° Celsius is important as 10 times more time is needed to contract collagen for every 5° drop in temperature [17]. This makes Renuvion® technology very efficient compared to many other technologies. In contrast, bulk heating devices (Thermi, InMode) uses a radial pattern of heat directed primarily to the dermis that is maintained at optimal temperatures for comparatively prolonged time (>120 sec) for maximum contraction to occur, thereby increasing treatment times and requiring constant monitoring of epidermal temperatures [1].

Within the operative sequence, Renuvion® is utilized after tumescence and liposuction. It is important to note that the use of tumescent solution enlarges the space for handpieces to travel and provides a means for RF conduction, as adipose tissue is less conductive. Each access port is the apex and offers a fan shaped pattern for the handpiece strokes. The visible pattern and intensity of the plasma stream helps to direct depth during the process of multilayer volumetric heating. Prior to insertion of the handpiece, it is important to prime the handpiece by activating it against a metal instrument to visualize the plasma stream. For handpieces

#### *Contractile Effects of Radiofrequency Energized Helium Plasma on the Fibrous Septal Network DOI: http://dx.doi.org/10.5772/intechopen.97849*

that have a retractable blade electrode, it is also important to ensure the blade is retracted prior to insertion. The minimal amount of helium gas (L/min) necessary to ensure a good bridge or connection to deliver the RF energy to the tissues should be utilized. The use of counter ventilation port permits egress of excess helium gas, avoidance of gas tracking and postoperative crepitus. Re-suctioning after use of the handpiece may also reduce gas related sequalae, remove liquified and fragmented cells and free fatty acids, and remove residual heated tumescent fluid that may lead to an unpredictable tissue response. The RF energy should be delivered using smooth, continuous movement of the handpiece. It can be monitored by the trans-illumination of the plasma stream in tissue, and activation should be stopped within 1 cm of the access port to prevent overheating of this area from repeated contact. There are indication lines on the handpiece shaft within 40 mm of the tip that visually guide the surgeon as to when to stop handpiece activation. A variety of handpiece lengths, diameters, flexibility and single or twin port options are available. Compressing or gathering the tissue around the handpiece with the other hand allows for directing and monitoring handpiece placement, intended plane and depth of treatment, provides more substrate to the RF energy path with each stroke, and avoids heating nontarget structures, like muscles. Tactile feedback from the non-handpiece hand offers a sense of decreasing soft tissue laxity and confirms there is no rise in skin temperature. Recall that the threshold for epidermal burns is significantly lower than the optimal temperature for collagen contraction. Error codes will provide audible warnings of gas occlusions from tip obstruction and immediately stop the delivery of RF energy in the handpiece. Deactivation of the unit and power output will occur with gas flow faults. Like bulk heating devices, the amount of time-on-tissue and energy delivered should be reduced in areas of thin skin, thin adipose layers, pre-existing scar tissue or compromised blood flow [13]. Moreover, Renuvion® is not well suited for patients with collagen vascular diseases, poorly vascularized tissue, pre-existing fibrosis or skin compromise, or lifestyles that might impair collagen remodeling such as smoking, poorly controlled diabetes, chronic NSAID use, and in patients with implantable devices that can attract the RF energy preferentially over the grounding electrode [27]. Results are likely to be limited in regions of compromised soft tissue as evidenced by open wounds, severe pendulosity, severe laxity and/or striae.

In general, Renuvion® provides reproducible, safe, well-tolerated soft tissue contraction three dimensionally and abrogates the risk of laxity. There is a 2D or linear contraction of collagen changes in the deep dermis, and 3D contraction of fascia, septal connective tissue that separates fat lobules and connects fascia to dermis, and reticular fibers that provide the framework of collagen fibers that encase fat cells [28]. Histologically, collagen bundle alignment in multiple directions is seen. The nonuniform geometry of the different components leads to a range of soft tissue remodeling results, regardless of the energy applied. Targeting the interstitial connective tissue bands without the need for full thickness dermal heating provides faster treatment times in comparison to bulk heating devices, with superior overall soft tissue contraction. Given interpatient variability in available FSN substrate, establishing clinical guidelines for consistent and predictable results is proving challenging. Recent single and multi-center chart reviews have demonstrated high patient satisfaction along with the safe and effective use of Renuvion® as an adjunct to enhance liposuction outcomes [21, 29, 30]. Consistent and reproductible soft tissue contraction was demonstrated even in the clinically challenging area of the neck area by subjective and quantitative analyses of before and after photographs [21]. Current studies are underway attempting to quantify the amount of energy deposited as kilojoules delivered per area and correlate them with resulting changes in soft tissue laxity.
