In vitro study on the thermal effects of holmium laser lithotripsy in flexible ureteroscopy

To investigate the impact of surgical parameters (power, pulse width, and irrigation flow rate) on thermal effects during flexible ureteroscopic holmium laser lithotripsy using an in vitro model, to optimize surgical conditions and minimize thermal damage. An in vitro upper urinary tract model was constructed to simulate the human upper urinary tract environment. Under the same power (36 W), different energy and frequency, pulse duration (long pulse duration and short pulse duration), and irrigation flow rate (0 mL/min, 30 mL/min, 60 mL/min) were set, and the temperature changes within 120 s of laser application were recorded. At 120 s of laser activation, under identical pulse width, irrigation flow rate, and power output (36 W), no statistically significant difference in temperature was observed between the 1.8 J/20 Hz and 1.2 J/30 Hz energy/frequency settings (P > 0.05). Under the same power settings without irrigation, the long-pulse group exhibited significantly higher localized temperatures than the short-pulse group (P < 0.05). However, when the irrigation flow rate reached ≥30 mL/min, the temperature difference between long-pulse and short-pulse modes became statistically insignificant (P > 0.05). Notably, at irrigation flow rates ≥30 mL/min, all experimental groups maintained temperatures within the safe range (<43 °C, a widely recognized threshold for thermal injury onset). initiation flow rate is a key factor in controlling thermal effects. Maintaining an irrigation flow rate > 30 mL/min can effectively reduce the risk of urothelial injury. Long pulse duration generates more heat than short pulse duration, so the pulse width should be carefully selected to optimize surgical safety.