Percutaneous nephrolithotomy requires continuous irrigation. The resulting intrarenal pressure increase may cause renotubular reflux of potentially contaminated fluid. The threshold value for reflux has been established in historic publications at 30 mmHg.
The aim of this work was to study in different models the regional pressure transmission and maximum pressure for different PNL systems.
We studied the Ultra-Mini-PNL-system (UMP, Fa. LUT, Germany, outer shaft diameter 13 Fr), a Mini-PNL-system (MPNL, Richard Wolf, Germany, shaft 18 Fr, nephroscope 12 Fr) and a Standard-PNL-system (SPNL, Richard Wolf, Germany, shaft 27 Fr, nephroscope 24 Fr). All experiments were performed with continuous and stable irrigation flow maintained with an irrigation pump (LUT, Germany).
The instruments and pump were provided by the manufacturers.
In an open model the regional pressure transmission of the jetting pressure was investigated. Maximum pressures were measured in a closed model. For a more realistic simulation of the conditions in the pelvicaliceal system (notably its expansibility) additional experiments were performed with porcine kidneys ex vivo. Several measuring sensors were applied and the results evaluated mathematically.
In the open system we observed pressure elevation only in a concentric area in front of the irrigation channel. Beyond 3 cm distance no pressure elevation could be measured.
In the closed model we found maximum pressures of 49 mmHg (UMP), 16 mmHg (MPNL) and 16 mmHg (SPNL) if the nephroscope was pushed to the end position inside the outer shaft. When the nephroscope was pulled out 0.5 cm inside the outer shaft the pressures were more equilibrated: 16 mmHG (UMP), 17 mmHg (MPNL) and 21 mmHG (SPNL). In the porcine kidneys we measured maximum pressures of 15 mmHg (UMP), 5 (MPNL) and 8.5 (SPNL) if the nephroscope was pushed to the end position. When the nephroscope was pulled back the pressures were below 10 mmHg for all the systems.
During application under normal circumstances the maximum pressures in the models were below the critical threshold value of 30 mmHg for all the systems investigated.
It is of note that high pressures were measured for the UMP system if the nephroscope is pushed to the end position. The reason seems to be the conical shape of the nephroscope which can close the space between nephroscope and outer shaft almost completely, thus obstructing the outflow. This point seems to be of clinical importance and should be considered during everyday practice.