Variables affecting proper system grounding for radiofrequency ablation in an animal model

PURPOSE: The authors sought to determine which factors contribute to excessive thermal deposition and burns at the grounding pad site after high-current percutaneous, image-guided radiofrequency (RF) ablation, MATERIALS AND METHODS: Radiofrequency (1,000-2,000 mA) was applied for 10 minutes with use of an internally-cooled electrode placed into in vivo pig livers (n = 88), In separate experiments, the number of pads (1, 2, or 4), orientation of pads (horizontal, vertical, or diagonal), and distance between the pads and the electrode (10-50 cm) of mesh or foil grounding pads (12.5 x 8 cm; 100 cm(2)) were varied. Thermistors measured skin surface temperatures during ablation, Pathologic analysis of skin changes was performed. RESULTS: Temperature elevations at the grounding pad were observed for every trial, with a temperature elevation greater than or equal to 12 degrees C (as high as 45 degrees C) observed in 60 of 88 trials (68.2%). Temperatures at the grounding site pad were dependent on all variables studied, including the grounding pad surface area, the amount of current deposited in the liver, the orientation of the pad, and the pad's distance from the electrode. Second-degree burns were seen with temperatures exceeding 47 degrees C and third-degree burns were observed when a temperature greater than or equal to 52 degrees C was noted. For a given set of RF parameters, reduced heating was observed for trials in which foil grounding pads were used (P < .001), Grounding pad burns did not occur at 2,000 mA (maximum generator output) when four foil pads were placed horizontally greater than or equal to 25 cm from the electrode. CONCLUSIONS: High-current RF ablation can induce severe burns at the grounding pad site if inadequate precautions are taken. To minimize the risk of burns, multiple large-surface-area foil pads should be placed on well-prepared skin and oriented with the longest surface edge facing the RF electrode.