Abstracts
2002 Digestive Disease Week

# 101518 Abstract ID: 101518 Saline-Linked Surface RF Ablation: Determination of Causal Factors and Prevention of Steam Popping
Steven Strasberg, Michael McKlurken, Stefan Topp, David Lipson, Gundumi Upadhya, David Linehan, st louis, MO; Dover, NH

Saline cooled surface RF ablation is a new modality to deliver destructive energy to surface liver tumors or resection margins. Saline cooling prevents charring and resultant current dampening due to increase in impedance. It thereby permits higher levels of total energy delivery. In preliminary experiments in pigs we produced lesions 4cm in diameter and 2cm in depth in 9 minutes. However, as only the surface is cooled, temperatures within the tissue may rise above 100oC with resulting undesirable steam formation and expansion that lead to tissue disruption ("popping"). We have modeled this phenomenon, performed experiments on pigs to determine the validity of the model, and determined the parameters that predict popping. Methods: 90 surface lesions were created in the livers of six anesthetized pigs using a saline linked RF ablation system (TissueLink Inc). Variables were lesion size (1,2 or 4 cm.), power (10-100Watts) and inflow occlusion (+ or -). Time of application was constant, based on preliminary experiments. Results: The model predicted a threshold power Pt for popping. Above that power, popping would occur rapidly and more rapidly as power exceeded Pt. Below Pt popping would never occur. It also predicted that popping was dependent on the diameter of the lesion, and minimally dependent on inflow occlusion. Experimental results bore out the predictions of the model. Popping occurred at lower powers in smaller lesions. As shown for 2cm lesions, (figure) popping was dependent on power and minimally dependent on inflow occlusion. Pt was 15W for 1cm lesions, 25 W for 2 cm lesions and about 80W for 4cm lesions. Conclusions: Pt for steam popping of surface RF lesions in pig livers has been determined. Steam popping may be prevented by maintenance of power below Pt. Creation of larger lesions that give time for heat to dissipate will permit higher power inputs without popping. Inflow occlusion has a small effect on steam popping