Evaluating safe irrigation rates for Tm fiber laser lithotripsy to prevent thermal injury: an in vitro and numerical simulation.

PURPOSE: To evaluate temperature changes and thermal injury during thulium fiber laser (TFL) lithotripsy in the urinary tract and identify the safe irrigation rate, providing a reference for optimal parameter settings in clinical practice.

METHODS

An in vitro thermal injury experiment was conducted using a home-made TFL operating at 40 W. The experiment utilized a glass tube simulating the urinary tract. A peristaltic pump circulated 25 °C saline at irrigation rates ranging from 10 to 40 mL/min. Real-time temperature measurements were recorded using thermocouples, and thermal injury was assessed by calculating the thermal dose threshold. Additionally, a validated numerical simulation model was developed to analyze temperature distributions and predict safe irrigation rates at 20 and 30 W.

RESULTS

In the in vitro experiment, at 40 W, severe thermal injury occurred in the urinary tract when the irrigation rate was below 30 mL/min, particularly in the ureter and renal calyx. The numerical simulation model demonstrated a high degree of consistency with the experimental results. According to the simulation, at 30 W, thermal injury occurred in the renal calyx when the irrigation rate was below 20 mL/min. At 20 W, thermal injury was observed in the renal calyx when the irrigation rate was below 10 mL/min.

CONCLUSIONS

The increase in temperature and the extent of thermal injury were strongly dependent on laser power and irrigation rate, with a lesser dependence on anatomical location. The accuracy of the numerical simulation was validated through experiments, demonstrating its capability to reliably predict temperature variations and thermal injury under different laser power settings and irrigation rates.