Sequential activation of multiple grounding pads reduces skin heating

Radio frequency (RF) tumor ablation has become an accepted treatment modality for tumors not amenable to surgery. The need for larger ablation zones has required increase in RF generator power, with current generation devices delivering 200-250 W. Skin burns due to ground pad heating have become a common complication and are now a limiting factor for further increase in ablation zone and generator power. We performed ex vivo experiments with three ground pads (5 x 5 cm) placed on a tissue phantom. We applied 100 W of power for 12 min between the pads, and an RF electrode while we measured leading edge temperature below each pad, and temperature profile on the pads using temperature-sensitive LCD-paper. We compared conventional operation (i.e. simultaneous connection of all three pads) to sequential activation of the pads where each pad is only active for approximately 0.5 s. The timing during sequential activation was adjusted to keep leading edge temperature equal between the pads. Temperature rise below the leading edge for proximal, middle and distal ground pad was 10.7 +/- 1.04, 1.0 +/- 0.15 and 0.3 +/- 0.07 degrees C for conventional operation, and 4.8 +/- 0.16, 4.4 +/- 0.20 and 4.5 +/- 0.35 degrees C for sequentially activated operation. The maximum leading edge temperature rise was more than twice as high for conventional compared to switched operation (p<0.001). Sequential activation of multiple ground pads resulted in reduced maximum leading edge temperature, and allows control of each pad such that leading edge temperature of all pads is the same. This may reduce the incidence of ground pad burns by allowing each pad to reach same temperatures independent of location, and may allow higher power RF generators due to reduced skin heating.