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EAU 2018: Intrarenal Pressure During Percutaneous Nephrolithotomy – Ex Vivo Measurements For Different PNL Systems

Copenhagen, Denmark (UroToday.com) Dr. Wilhelm, clinical urologist from the University of Freiburg in Freiburg, Germany, presented his study’s results on the effect of percutaneous nephrolithotomy (PNL) systems on intrarenal pressures. The justification behind this experiment stems from the necessity of continuous irrigation during PNL and the implications it has on the surrounding tissue. An elevated intrarenal pressure could potentially harm the patient by causing renotubular reflux of potentially contaminated fluid, for example. Previous studies have also researched this topic and guidelines have shown that the threshold for renotubular reflux is at 30 mmHg. This study, as intended by Dr. Wilhelm, was to study different models of the kidney to determine the maximum pressures of certain PNL systems.

This study analyzed an Ultra-Mini-PNL-system (UMP), a Mini-PNL-system (MPNL), and a standard-PNL-system (SPNL) with continuous and stable irrigation flow maintained by an irrigation pump throughout the experiment. It is worth noting that the instruments and pump was provided by the manufacturers themselves. Two models were used: an open model to determine regional pressure during jetting and a closed model for maximum pressure measurements. Furthermore, a porcine kidney was used as an ex vivo model to study a more realistic simulation of the pelvicalyceal system. Several measuring senseors were applied to each model to determine the most accurate pressures.

Through testing with the open model, there was only a pressure change directly in front of the irrigation channel. Three centimeters and beyond resulted in no measurable pressure elevation. In the closed model with the nephroscope pushed to the end position within the outer shaft, 49 mmHg, 16 mmHg, and 16 mmHg were measured for UMP, MPNL, and SPNL systems, respectively. With the nephroscope pulled out 0.5 cm within the outer shaft, 16 mmHg, 17 mmHg, and 21 mmHg were found for UMP, MPNL, and SPNL systems, respectively. Within the porcine kidne, the maximal pressures for the nephroscope pushed to the end position for UMP, MPNL, and SPNL were 15 mmHg, 5 mmHg, and 8.5 mmHg, respectively. If the nephroscope was pulled back, the pressures dropped below 10 mmHg for all systems in all models.

During experimentation of renal pressures in a normal circumstance with the porcine kidney, all pressures from each PNL system stayed below the threshold value of 30 mmHg. Dr. Wilhelm wanted to further explain his results by reiterating that high pressures were noticed if the nephroscope was pushed to the end position, likely due to the conical shape of the scope itself. He hoped to instruct all urologic surgeons in attendance to consider this during everyday practice to avoid patient complications.

Presenter: K. Wilhelm

Authors: Wilhelm K. , Schulze-Ardey J. , Spaeth J. , Schumann S. , Miernik A.

Written by: Zachary Valley, University of California-Irvine, at the 2018 European Association of Urology Meeting EAU18, 16-20 March, 2018 Copenhagen, Denmark