Thermal Safety Boundaries for Laser Power and Irrigation Rate During Ureteroscopy: In Vivo Porcine Assessment With a Ho:YAG Laser

Abstract

To map thermal safety boundaries during ureteroscopy (URS) with laser activation in two in vivo porcine subjects to better understand the interplay between laser power, irrigation rate, and fluid temperature in the collecting system. URS was performed in two in vivo porcine subjects with a prototype ureteroscope containing a thermocouple at its tip. Up to 6 trials of 60seconds laser activation were carried out at each selected power setting and irrigation rate. Thermal dose was calculated for each trial, and laser power-irrigation rate parameter pairs were categorized based on number of trials that exceeded a thermal dose of 120 equivalent minutes. The collecting fluid temperature was increased with greater laser power and slower irrigation rate. In the first porcine subject, 25W of laser power could safely be applied if irrigation was at least 15mL/min, and 48W with at least 30mL/min. Intermediate values followed a linear curve between these bounds. For the second subject, where the calyx appeared larger, 15W laser power required 9mL/min irrigation, 48W required 24mL/min, and intermediate points also followed a near-linear curve. This study validates previous bench research and provides a conceptual framework for selection of safe laser lithotripsy settings and irrigation rates during URS with laser lithotripsy. Additionally, it provides insight and guidance for future development of thermal mitigation strategies and devices.