Effect of Chilled Irrigation on Caliceal Fluid Temperature and Time to Thermal Injury Threshold During Laser Lithotripsy: In Vitro Model

Introduction: High-power lasers (100–120 W) have widely expanded the available settings for laser lithotripsy and facilitated tailoring of treatment for individual cases. Previous in vitro and in vivo studies have demonstrated that a toxic thermal dose to tissue can result from treatment within a renal calix. The objective of this in vitro study was to compare thermal dose and time with tissue injury threshold when using chilled (CH) irrigation and room temperature (RT) irrigation. Materials and Methods: A glass tube attached to a 19 mm diameter bulb simulating a renal calix was placed in a 37°C water bath. A 242 μm laser fiber was passed through a ureteroscope with its tip in the center of the glass bulb. A wire thermocouple was placed 3 mm proximal to the ureteroscope tip to measure caliceal fluid temperature. RT at 19°C or CH at 1°C irrigation was delivered at 0, 8, 12, 15, or 40 mL/minute. The laser was activated at 0.5 J × 80 Hz (40 W) for 60 seconds. Thermal dose was calculated using the Sapareto and Dewey t43 methodology with thermal dose = 120 equivalent minutes considered the threshold for thermal tissue injury. Results: At each irrigation rate, CH irrigation produced a lower starting temperature, a lower plateau temperature, and less thermal dose compared with RT irrigation. The threshold of thermal injury was reached after 13 seconds of laser activation without irrigation. With 12 mL/minute irrigation, the threshold was reached in 46 seconds with RT irrigation but was not reached with CH irrigation. Conclusion: As higher power laser lithotripsy techniques become further refined, methods to mitigate and control thermal dose are necessary to enhance efficiency. CH irrigation slows temperature rise, decreases plateau temperature, and lowers thermal dose during high-power laser lithotripsy.