A novel hydrodynamic design greatly improves the debris clearance rate of flexible ureteroscopy.

OBJECTIVES: To introduce a novel hydrodynamic design for a flexible ureteroscope that can increase stone debris clearance.

METHODS: Based on hydrodynamics, the new design allowed the ureteroscope to have six water jets. Fluid gushed from the six jets and would ultimately converge into an eddy. The safety and stone debris clearance efficiency were tested in a 3D-printed kidney model. Stone fragments between 0.5 and 1 mm were used to mimic the debris. A ureteroscope already approved for marketing was used as a control.

RESULTS: The new design did not change the local renal pressure and did not raise the whole renal pressure under irrigation at 80 or 100 mL/min but slightly raised it under irrigation at 120 mL/min. The pressures in the 2 g stone clearance procedures were 26.0, 33.1, and 37.5 cmH2O for the new design and 25.1, 30.2, and 39.3 cmH2O for the current design; in the 4 g stone clearance procedures, the pressures were 30.1, 37.2, and 40.0 cmH2O for the new design and 26.9, 30.8, 39.8 cmH2O for the current design, all under conditions of 80, 100, 120 mL/min irrigation, respectively. The new design significantly improved the stone-clearance rate by nearly tenfold. It successfully cleared 2 g and 4 g stones within 900 s under the three irrigation rates. In contrast, the current design cleared less than 10％ of the stone debris in all tests.

CONCLUSION: The new hydrodynamic design significantly improved the stone debris clearance rate without causing obviously increased renal pressure, and the improvement was maintained under different irrigation pressures and stone burdens.