Sand clearance vs. flowrate during ureteroscopy: studies in an in-vitro transparent kidney model.

Purpose: Suction has recently been introduced into the ureteroscopic armamentarium to improve stone fragment and debris clearance. However, the benefits of suction appear to be limited by current irrigation systems. This study aimed to measure the time to clear sand ureteroscopically from a transparent silicone kidney-ureter model at different flowrates and compare with results with conventional pressurized irrigation and intermittent suction.

Methods: A LithoVue™ Elite ureteroscope was inserted through a Clear Petra 11/13 Fr 46 cm or 12/14 Fr 50 cm FANS device into a transparent silicone kidney model. Irrigation was delivered from a peristaltic pump at rates of 18-90 ml/min with pump assisted outflow or from a pressurized source with suction assisted outflow. Intrarenal pressure (IRP) was maintained between 30-40 cmHO. Trials were conducted to measure the time required to completely aspirate 0.5 g of sand from the mid and upper calyces.

Results: Sand was cleared more quickly from the kidney model as flowrate increased up to ~ 70-80 ml/min. Use of continuous flowrate was more efficient at clearing sand than variable flowrate produced by bursts of intermittent suction.

Conclusions: Flowrate is a primary variable affecting efficiency of sand clearance in in vitro studies. Current clinical methods that utilize intermittent suction during ureteroscopy are likely less efficient than configurations that provide continuous flowrates. Incorporation of IRP feedback into irrigation systems may facilitate high flowrate while maintaining stable low IRP, thereby enhancing efficiency and safety of ureteroscopy.