Flow matters 2: How to improve irrigation flow in small-calibre percutaneous procedures-the purging effect

Aim of this study was to investigate whether the combination of high-pressure irrigation inflow combined with simultaneous sensor-controlled suction could improve irrigation turnover without leading to high peak intrarenal pressure in small-calibre percutaneous instruments (SCPI). M + M: A MIP XS sheath (9.5 Fr. outer diameter and 8.5 Fr. inner diameter) and a 7.5-Fr. nephroscope (3-Fr. irrigation channel; MIP XS by Nagele, Karl Storz, Tuttlingen, Germany) was inserted into the collecting system of a non-perfused cadaveric porcine kidney, an 8-Fr. mono-J catheter was introduced through the ureter. Irrigation was performed using a pressure-controlled, combined irrigation/suction pump (Uromat E.A.S.I., Karl Storz, Tuttlingen, Germany) in either single-flow or continuous-flow (=combination of irrigation and suction) mode. Intrarenal pressure was measured and irrigation fluid turnover was measured by a cystometry catheter inserted trans-parenchymally into the renal pelvis. Pressure changes were recorded by a urodynamic workstation.

Applying pressure-controlled suction, irrigation fluid turnover could be increased by 5 % at an inflow pressure of 75 mmHg (80-84 ml/min) and 15 % at an inflow pressure of 110 mmHg (196-110 ml/min). Suction decreased the intrarenal pressure by 14 % at 75 mmHg (19-14.5 cm H2O) and 28 % at 110 mmHg inflow pressure (37-26.5 cm H2O).

Although combination of pressure irrigation with sensor-controlled suction increases irrigation flow in SCPI, the intrarenal pressure could be reduced with combined suction via a transurethral mono-J catheter. This irrigation method in percutaneous surgery is called purging effect.