Bubble Trouble: The Thermal Risk of Ureteral Laser Lithotripsy in an Air Bubble.

INTRODUCTION

During ureteroscopic laser lithotripsy (URSL), unsafe elevations in ureteral temperature are thought to contribute to ureteral stricture formation. Cellular damage begins at 43°C, and proteins denature instantly at 60°C. Air bubbles may inadvertently migrate into the collecting system during URSL. The purpose of this study was to evaluate ureteral temperatures during simulated URSL in an air bubble with a holmium (Ho:YAG) and thulium fiber laser (TFL).

METHODS

BegoStone phantoms were positioned distal to the ureteropelvic junction in a model kidney and ureter submerged in a 35°C saline bath. A 7.5 Fr flexible ureteroscope was advanced to the stone, and continuous saline irrigation at 22°C was maintained at 15 mL/min. A needle thermocouple positioned 2 mm from the laser fiber tip monitored ureteral wall temperature. A 200 µm laser fiber was then advanced until it contacted the stone. The Ho:YAG and TFL were used in 5 trials each to ablate stones at 3, 10, and 20 W in saline and in a 3 mL air bubble.

RESULTS

In the control condition, neither laser exceeded 43°C at 3, 10, or 20 W. In an air bubble, ureteral temperatures exceeded 43°C after 1 second at 3 W for both TFL and Ho:YAG. At 10 W, the Ho:YAG exceeded 43°C after 1 second, while the TFL exceeded 60°C. The average temperature exceeded 60°C at 20 W for both lasers after 1 second. Both lasers generated much higher temperatures in an air bubble than in saline at all time points (p = 0.008), with maximum temperature exceeding 250°C for both lasers.

CONCLUSION

In this benchtop model, laser activation in an air bubble for 1 second exceeded the thermal safety threshold at ≥ 3 W and risks protein denaturation at ≥ 20 W. This study highlights the importance of avoiding air bubbles during URSL to maintain safe ureteral temperatures. Further studies are needed to validate these findings in vivo.