Characterization of Flow-Caused Intrarenal Pressure Conditions During Percutaneous Nephrolithotomy In Vitro

To investigate renal pelvic pressures during percutaneous nephrolithotomy (PCNL) in the standard, mini, and ultramini PCNL systems. We studied an ultramini PCNL system (UMP, outer shaft diameter 13F), a mini PCNL system (MPCNL, shaft 18F, nephroscope 12F), and a standard PCNL system (SPCNL, shaft 27F, nephroscope 24F). Pressure profiles were first investigated in an open model setup, subsequently in a closed model, and finally in an ex vivo porcine kidney. Measurements were determined with the nephroscope in an advanced and pulled-back position for all models. In the advanced position, maximum pressures of 41.61 ± 0.20 mmHg (UMP), 15.61 ± 0.15 mmHg (MPCNL), and 15.46 ± 0.14 mmHg (SPCNL) were measured in the closed model. In the pulled-back position, maximum pressures were 16.04 ± 0.22 mmHg (UMP), 17.02 ± 0.11 mmHg (MPCNL), and 20.50 ± 0.11 mmHg (SPCNL). In the ex vivo porcine kidney model, maximum pressures were 13.81 ± 6.04 mmHg (UMP), 5.64 ± 0.21 (MPCNL), and 9.21 ± 0.52 (SPCNL) with the nephroscope pushed to end position. After retracting the nephroscope from the outer shaft, pressures in all systems did not exceed 10 mmHg. The maximum pressures achieved with the three PCNL systems in all three models were kept below the 30 mmHg critical threshold value. High pressures were only determined for the UMP system with the nephroscope pushed to its end position. This was attributed to the conical shape of the nephroscope, which occupies the space between the nephroscope and outer shaft, resulting in outflow obstruction.