Optimizing infusion-suction diameter ratio (ISDR) in ureteroscopy: in vitro pressure and flow prediction and management

Abstract

To optimize channel configurations for a flexible ureteroscope incorporating both irrigation and suction channels, in vitro experiments were conducted with the aim of achieving safer and more efficient surgical procedures. Upper urinary tract models with integrated pressure-sensing ports were constructed based on CT urography reconstructions. Functional ureteroscope prototypes with various combinations of infusion and suction channel diameters were developed. Using a controlled constant-pressure irrigation system, intrarenal pressure measurements were obtained from the upper, middle, and lower calyces, as well as the renal pelvis. The effects of varying infusion pressures on irrigation flow rates and intrarenal pressure distribution were assessed. Regression models were subsequently established for renal pelvic pressure (RPP) and irrigation flow rate, allowing for the determination of the optimal channel diameter configuration by integrating model predictions with clinical requirements. At an infusion pressure of 500 cmH₂O without active suction, the maximum Infusion-to-Suction Diameter Ratio (ISDR) that maintained RPP below the safety threshold was approximately 0.525, corresponding to an Infusion-to-Suction cross-sectional Area Ratio (ISAR) of about 0.276. Theoretically, the optimal combination of infusion and suction channel diameters that satisfies both pressure and flow criteria is 1.03 mm and 1.93 mm, respectively. These findings demonstrate that the ISDR, infusion channel caliber, and irrigation pressure are critical determinants of RPP and flow rate during ureteroscopic procedures. For ureteroscopes with integrated infusion and suction channels, maintaining an ISDR below 0.525-or an ISAR below 0.276-provides favorable balance between procedural safety and irrigation efficiency.

Keywords: Design; Flexible ureteroscope; Hydrodynamics; Renal pelvic pressure.