Concentration and volume effects in thermochemical ablation in vivo: Results in a porcine model

Purpose: To explore the effects of volume and concentration in thermochemical ablation using an in vivo porcine model. Methods: Twelve swine 6075kg were used in this institutionally approved study. A needle design prototype coaxial device for reagent injections and a thermocouple were inserted into surgically exposed liver. Simultaneously, an acid and base (acetic acid and NaOH) were injected at 4mL/min based on a 3×3 matrix with concentration (5, 10, and 15mol/L) and volume on the axes (total volumes of 1, 2, and 4mL). Three animals (centre grid position) strengthened the statistical analysis. Each animal received four identical injections (total 48). Temperatures and heart rate were recorded. Livers were formalin-fixed after sacrifice. After sectioning, coagulation zones were analysed by two observers. Area and slice thickness were used to calculate the volume, surface area, and sphericity for each treatment. Results: Coagulation volumes ranged from 2.95±0.29 to 14.72±1.42mL with a maximum of 18.3mL. Highest peak temperature was 105°C with temperatures ranging 43.5±2.6°C to 91.0±6.5°C. There was no association between conditions and sphericity or heart rate. Conclusions: The method can be used successfully to ablate tissue in vivo. By neutralising acid in situ and releasing heat and a salt, this technique improves considerably upon the use of acetic acid used alone. Peak temperatures exceeded accepted coagulation thresholds even if the only mechanism operating was hyperthermia. Reagent concentrations and volumes increased the amount of the coagulum but not in a linear fashion.