Ureteral Tissue Temperature During Ureteroscopy With Ho:YAG Laser Activation in an In Vivo Porcine Model

To measure temperature of the outer ureteral wall and calculate thermal dose with different irrigation and laser power settings during ureteroscopy in a porcine in vivo model.

The ureters of two porcine subjects were exposed through laparotomy incisions. A length of PFA tubing, with equally spaced windows, was inserted into the ureter through a ureterotomy. An array of thermocouples was positioned on the outside of the ureter, colocated with the windows. A LithoVue Elite (Boston Scientific) ureteroscope with a wire thermocouple attached was inserted into the tube adjacent to the ureteral windows. Trials of 60 seconds laser activation were performed at different power and irrigation rates. Thermal dose was calculated at each thermocouple with the threshold of thermal injury considered to be 120 equivalent minutes.

All trials conducted with 8 mL/min irrigation: 20 W laser power produced elevated ureteral temperatures. Thermal doses exceeded the thermal injury threshold along a 3 cm length of ureter in some cases. 67% of trials using 15 mL/min irrigation: 30 W laser power also produced suprathreshold thermal doses within ureteral tissue. Employing a 50% operator duty cycle at these same settings decreased thermal dose below threshold. Thermal dose did not reach the threshold of thermal injury in any trials with 40 mL/min irrigation.

Ureteroscopy in a porcine model with commonly used irrigation rates and laser settings can elevate ureteral temperatures and produce thermal doses above the threshold of thermal injury.