Thermomechanics of electrosurgical procedures

Abstract

Starting with Pennes’ bioheat transfer equation to model the temperature profiles observed during ex vivo experiments, we show that the apparent specific heat of the tissue increases significantly at 100°C, highlighting the important role latent heat loss plays in energy dissipation. A proposed two-scale model that couples evaporation at the microscale with energy conservation at the macroscale is able to capture evaporation losses at 100°C and prevent further temperature increase. However, to account for the coupled effects of phase change of water in the intra- and extracellular spaces to vapor, vapor transport, and mechanical deformation, a more comprehensive thermo-mechanical model based on continuum mixture theory is proposed to accurately predict temperature in in vivo and ex vivo experiments on porcine liver tissue. We highlight the effect of applied power on tissue cutting and coagulation damage by coupling this model to an Arrhenius damage model to capture dynamic tissue heating during in situ electrosurgical cutting. The mixture model is coupled to a multi-frequency model to quantify the effect of frequency-dependent electrical properties on the rate of energy generation during ex vivo and in vivo electrosurgical tissue heating with multi-frequency power modes.