Caveat Emptor: The Heat Is "ON"-An In Vivo Evaluation of the Thulium Fiber Laser and Temperature Changes in the Porcine Kidney During Dusting and Fragmentation Modes

Introduction: We sought to examine the intrarenal fluid and tissue temperature alterations during dusting and fragmentation with the thulium fiber laser (TFL) in an in vivo porcine kidney. Materials and Methods: In two female Yorkshire pigs, temperature was continuously measured within the upper, interpolar, and lower calices along with the renal pelvis using multipoint thermal sensor probes; another temperature probe was situated at the tip of the ureteroscope. Four experimental protocols were performed for each animal: dual lumen ureteroscope with both warmed (37°C) irrigation and room temperature (20°C-22°C) irrigation and single lumen ureteroscope with warmed and room temperature irrigation. Of note, in each pig, one kidney underwent ureteroscopy (URS) with a 14F ureteral access sheath (UAS) in place, whereas the other kidney had no UAS placed. A 200-μm TFL fiber was fired at three laser settings: (1) dusting at 0.5 J, 80 Hz (40 W) with continuous activation until 5 minutes expired or a temperature of 44°C was reached, (2) low-power fragmentation 1 J, 10 Hz, (10 W), and (3) high-power fragmentation at 1.5 J, 20 Hz (30 W). In all cases, the pulse width was 1 ms. For fragmentation, the laser was activated for 10 seconds with a 2-second intermission for a 1-minute period (five cycles). Results: In the absence of a UAS, in all but one circumstance, temperatures reached or exceeded 44°C at all laser settings with the use of either warm or room temperature irrigation fluid, regardless of the type of ureteroscope used. Of concern, temperatures recorded at the tip of the URS were 4°C to 22°C less than the temperatures recorded in the renal calices. In contrast, with a 14F UAS in place, six distinct groups had temperatures that did not exceed 44°C, specifically at low- and high-power fragmentation settings with room temperature irrigation for both sets of ureteroscopes and at dusting and low-power fragmentation settings with warm temperature irrigation solely for the single lumen ureteroscope. Temperatures recorded at the tip of the ureteroscope with the deployment of a UAS yielded temperature differences ranging from 17°C less to 19°C more than the renal calices. Conclusions: TFL is a novel laser technology for lithotripsy. In the absence of a UAS, high-power TFL fragmentation settings in particular may create temperatures within the collecting system that could result in urothelial tissue injury. Of note, peak temperatures recorded at the tip of the ureteroscope may misrepresent the actual intrarenal temperature during TFL laser lithotripsy.