Assessing the Influence of Irrigation Flows on Clearance of Calculi Fragments During Percutaneous Nephrolithotomy: A Numerical and Physical Model Study

Objective: To analyze the intrarenal hydrodynamic processes and clearance of stone fragments during percutaneous nephrolithotomy (PCNL) using numerical and physical models. Materials and methods: COMSOL multiphysics software was used to simulate irrigation flows and transport of particles in a kidney model based on computerized tomographic acquisition. A similarly shaped physical model with solid particles was constructed, and PCNL was simulated using nephroscopes. The particles were tracked by a digital camera. Particle clearance in both models was compared at various flow velocities and angles. Results: The numerical model predicted a significantly increased particle clearance with high-velocity irrigation (0.25 vs 1 m/s, 12% vs 70%, respectively: P <.0001), as did the perpendicular positioning of the instrument (45° vs 90°, 1% vs 70%: P <.0001). These results were validated in the physical model with a correlation of r = 0.98. Particle clearance occurred only in the directly irrigated calyx. The flow and the particle movements in the other calices were negligible. The calculated intrarenal pressure at the maximal velocity reached 15.6 cmH ₂ O. Conclusion: Effective clearance of particles is achieved when irrigation is perpendicularly directed to the targeted calyx and enhanced by higher flow velocities. The flow in calyces that are not directly irrigated is ineffectual, and high flows do not significantly increase the intrarenal pressure. Validation of the numerical model by the physical model supports the use of computerized methods for advanced renal hydrodynamic research that may replace the need of some animal and human studies on the clearance of stones during PCNL.