Pelvicaliceal Volume and Fluid Temperature Elevation During Laser Lithotripsy

Background: While high-power laser systems facilitate successful ureteroscopic treatment of larger and more complex stones, they can substantially elevate collecting system fluid temperatures with potential thermal injury of adjacent tissue. The volume of fluid in which laser activation occurs is an important factor when assessing temperature elevation. The aim of this study was to measure fluid temperature elevation and calculate thermal dose from laser activation in fluid-filled glass bulbs simulating varying calix/pelvis volumes. Materials and Methods: Glass bulbs of volumes 0.5, 2.8, 4.0, 7.0, 21.0, and 60.8 mL were submerged in a 16-L tank of 37°C deionized (DI) water. A 230-μm laser fiber extending 5 mm from the tip of a ureteroscope was positioned in the center of each glass bulb. Irrigation with 0, 8, 15, and 40 mL/min of room temperature DI water was applied. Once steady-state temperature was achieved, a Ho:YAG laser was activated for 60 seconds at 40 W (0.5 J × 80 Hz, SP). Temperature was measured from a thermocouple affixed to the external tip of the ureteroscope. Thermal dose was calculated using the Dewey and Sapareto t43 methodology. Results: The extent of temperature elevation and thermal dose from laser activation were inversely related to the volume of fluid in each model and the irrigation rate. The time to threshold of thermal injury was only 3 seconds for the smallest model (0.5 mL) without irrigation but was not reached in the largest model (60.8 mL) regardless of irrigation rate. Irrigation delivered at 40 mL/min maintained safe temperatures below the threshold of tissue injury in all models with 1 minute of continuous laser activation. Conclusions: The volume of fluid in which laser activation occurs is an important factor in determining the extent of temperature elevation. Smaller volumes receive greater thermal dose and reach threshold of tissue injury more rapidly than larger volumes.