Purpose
Ground pad skin burns are a common complication during radiofrequency (RF) tumor ablation procedures, with incidences of 0.1 – 3.2% for severe skin burns (2nd or 3rd degree), and 5 - 33% for mild skin burns. Two device manufacturers have recently implemented monitoring current and temperature of ground pads to avoid skin burns. Current ground pads consist of a metal foil placed on top of an adhesive, electrically conductive polymer that attaches to the skin. We investigated a new ground pad design featuring two gel layers of differing electrical conductivity and compared this design to a current commercial ground pad in computer models and ex vivo experiments.
Material and methods
We created finite element computer models of current ground pad designs, and a double-layer design. We varied electrical conductivity of the layers as well as geometry to determine the ideal design that produces minimum skin heating. We then created gel layers (10% Agar-Water) of electrical conductivity as determined in the computer models by varying concentration of NaCl in the gel. We created ground pads by placing two 5 mm thick gel layers (20% NaCl, 2% NaCl for upper and lower layer, 100 x 130 mm) on top of each other, with a copper foil on top. We performed ex vivo experiments where we had a tissue phantom placed in saline solution with fresh pig skin including fat layer on top. We placed either a commercial ground pad, or our two-layer pad on top of the skin and applied 1.5 A RF current (~120 W power) for 6 min (n=4 each). We measured temperature below the leading edge as well as 1 cm in front, and 1 cm behind. In addition we measured temperature profile on top of the pads using thermo-sensitive liquid crystal paper.
Results
Skin temperature increase 1 cm in front, below, and 1 cm behind of the leading edge were 6.1 ± 0.2, 8.4 ± 1.1 and 4.2 ± 0.6 ºC for the commercial pad; temperatures were 3 ± 0.3, 2.9 ±0.2 and 1.5 ± 0.1 ºC for the double-layered design. The double-layered pad design produced significantly lower skin temperatures at all locations (p < 0.005), with maximum skin temperature reduced by a factor of 2.9.
Conclusion
The double-layered ground pad design resulted in significantly reduced skin temperatures within 1 cm from the leading edge. Maximum skin temperature increase was reduced by a factor of almost three. This may lower the incidence of ground pad burns, and may allow the use of higher power RF generators.