Clearance of Stone Fragments and Stone Dust by Continuous Flow Hydrodynamics in Percutaneous Renal Surgery: An In Vitro Study.

Purpose: To investigate the capacity of stone clearance in common percutaneous nephrolithotomy (PCNL) systems achieved solely by hydrodynamic effects in an in vitro setting.
Methods: A watertight cylindrical cast with a caliceal void served as an in vitro model. Various instruments for percutaneous renal surgery working with both continuous flow (fCF) and open Rutner sidearm (fCO) were tested. The model was loaded with standardized artificial stone material (2 mm in diameter) to examine stone removal by the vacuum cleaner effect and with sand (0.1-0.5 mm in diameter) to measure the washout effect caused by irrigation backflow. The association between washout of gravel and irrigation pressure was analyzed using ANOVA. Regression analysis was performed to assess the influence of the instruments' hydrodynamic characteristics-effective cross section of the outflow and irrigation flow volume.
Results: Provoking the vacuum cleaner effect removal of stones was only effective in fCF but not in fCO instruments. Depending on irrigation pressure, the volumetric flow rate and effective cross section of the outflow clearance of sand could be observed in various medium- and large-sized fCF and fCO instruments, whereas in small-sized systems, clearance effects were negligible. Regression analysis showed clearance of stone dust strongly associated with an instrument's volumetric flow rate.
Conclusions: This in vitro study demonstrated that the application of medium- and large-sized fCF PCNL systems removes both "insignificant" stones and dust solely by hydrodynamic effects. Further studies have to show if these effects also occur in the in vivo situation.