7. Characteristics of bulk heating devices

Traditional subcutaneous monopolar and bipolar radiofrequency devices utilize a small cannula that is placed underneath the skin to heat the adipose tissue. They are called bulk heaters because the thermal energy generated from the tip of the device heats the adjacent tissue from the point of emanation. The surrounding tissue becomes warm gradually in a radiant distribution. Monopolar RF has only a single source of subcutaneous energy, and heat must accumulate in the tissue from this small point. A grounding pad is needed to safely treat the patient (Figure 1). Bipolar devices maintain a zone of energy between two sources, in this case, one internal and the other external (Figure 2). If the external treatment head is small, it will take a while for the tissue between the two emitters to heat up. Broader external heads create wider fields of heated tissue and are more time efficient. Energy output also influences the speed of tissue heating. Tumesced tissue increases the permittivity of the adipose layer toward heat. If liposuction is indicated, it should be performed prior to energy application. Then, tissue heating is optimized, as the heat-resistant adipose shield will have been removed from the collagen bands of the fibroseptal network, which have lower impedance. Advantages of these device types include ease of use, a known performance history, and many experienced users. Limitations include a long duration of heating if treatment areas are broad. Even with an external sensor such as a FLIR camera or external thermistor, burns and seromas can occur. Clinical endpoints of treatment include warmth, erythema, and a slight tissue reaction when the cannula is moved under the skin. While the internal cannula tip can get to the preset temperature quickly, the surrounding tissue takes time to get warm. Thus, there are "hot spots," which may

#### Figure 1.

Monopolar soft tissue coagulation device. The heated tissue radius is small, as the cannula tip is not large. There is a central region that heats to a high temperature, but this rapidly drops down at the periphery. A grounding pad is needed in order to safely treat the patient.

#### Figure 2.

Bipolar configuration of a radiofrequency-assisted tissue tightening device. There is an internal and external heat sensor. The cannula is deployed in the subcutaneous fat in a manner similar to that of a liposuction cannula.

develop seromas, and areas where heating is not optimized. If the operator continues to heat a region that has already been optimally treated, cauterization of the microvasculature can cause ischemia, resulting in fibrosis or a burn. Knowing the amount of energy used is helpful, but a difficulty with any energy-based device is knowing when you are done. Factors that should reduce the amount of time and energy spent include an area with thin skin, a relatively thin layer of fat (such as the neck, face, and decollete), and any degree of existing fibrosis. FLIR studies show that when used in a primary case in the fibrous bra roll region, a bipolar device generated a skin temperature of 45°C for several minutes, even after the device was removed (Figure 3), despite the preset skin cutoff temperature being 38°C. A key to success when using these devices is to consider decreasing treatment time and measuring the skin temperature with FLIR in regions that have been previously treated and have some scar tissue and compromised blood supply. In fibrous areas, the physical nature of bulk heating can create a heat sink, due to the slow dispersion of heat. Compromised blood supply due to scarring or physical containment of heat Helium Plasma-Driven Radiofrequency in Body Contouring DOI: http://dx.doi.org/10.5772/intechopen.84207

Figure 3. Illustration of methods used in tissue temperature study.

is a region with fibrous fat which is a relative contraindication to the use of a subcutaneous bulk heating device.
