Thermal effect of holmium laser during ureteroscopic lithotripsy

Background: Holmium laser lithotripsy is the most common technique for the management of ureteral stone. Studies founded that holmium laser firing can produce lethal heating which will cause thermal injury towards ureter. The aim of our current study is to explore factors affecting thermal effect of holmium laser during ureteroscopic lithotripsy.Materials and Methods: An in vitro experimental model is design to simulate the ureteroscopic lithotripsy procedure. Different laser power settings (10w (0.5JX20Hz, 1.0JX10Hz), 20w (1.0JX20Hz, 2.0JX10Hz), 30w (1.5JX20Hz, 3.0JX10Hz)) with various firing time (3s, 5s, 10s) and irrigation flow rates（10ml/min, 15ml/min, 20ml/min and 30ml/min）were employed in the experiment. The temperature around the laser tip was recorded by thermometer.Results: The temperature in the “ureter” rises significantly with the increasing laser power, prolonging firing time and reducing irrigation flow. The highest regional temperature is 78.0℃ at the experimental set-up, and the lowest temperature is 23.5℃. Higher frequency setting produces more heat at the same power. Laser power<=10w, irrigation flow>=30ml/ml and “high-energy with low-frequency” can permit a safe working temperature.Conclusion: We clarify that the thermal effect of holmium laser is related with both laser working parameters and irrigation flow. The proper setting is the key factor to ensure the safety during ureteroscopic holmium laser lithotripsy.