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.

Introducing a Novel In Vitro Model to Characterize Hydrodynamic Effects of Percutaneous Nephrolithotomy Systems.

PURPOSE: To widen the understanding of the fluid mechanics during percutaneous nephrolithotomy (PCNL), a new in vitro model for empiric studies was developed. Our first aim was to characterize common PCNL systems with regard to their intrapyelocaliceal pressure and their irrigation flow volume as possible parameters of hydrodynamic invasiveness. MATERIALS AND METHODS: The model is based on a watertight cylindrical cast. Low pressure miniaturized PCNL (miniPCNL) systems and conventional PCNL systems were tested. Intrapelvic pressure and the total of irrigation flow volume per minute were measured for each PCNL system at 10 predefined levels of irrigation pressure between 40 and 130 cm H2O. RESULTS: Linear regression showed a linear relation between irrigation pressure and intrapelvic pressure. Compared with miniPCNL systems, conventional PCNL sheaths with closed Rutner sidearm generate significantly higher intrapelvic pressures. Opening the Rutner sidearm leads to a decrease in intrapelvic pressure to the level of the open mini PCNL systems. Polynomal regression revealed a square root relation between irrigation pressure and irrigation flow volume. CONCLUSIONS: Our in vitro model is suitable for obtaining reliable and valid data of intrapelvic pressure and irrigation flow volume of commonly used PCNL systems. Conventional PCNL sheaths with opened Rutner sidearm provide intrapelvic pressure and irrigation volume similar to miniPCNL. Consequently, a relevant difference of the hydrodynamic impact between conventional and miniPCNL systems are not necessarily to be assumed. Regression analysis revealed a new starting point for further empiric research of fluid mechanics during PCNL.