Renal pelvis pressure and flowrate with a multi-channel ureteroscope: invoking the concept of outflow resistance.

Understanding renal pelvis pressure (P) during ureteroscopy (URS) has become increasingly important. High irrigation rates, desirable to maintain visualization and limit thermal dose, can increase P. Use of a multi-channel ureteroscope (m-ureteroscope) with a dedicated drainage channel is one strategy that may facilitate simultaneous low P and high flowrate. We sought to define the relationship between P and flowrate across a range of different outflow resistance scenarios with an m-ureteroscope versus a single-channel ureteroscope (s-ureteroscope). The m- or s-ureteroscope was placed into the pelvis of a validated silicone kidney-ureter model. Trials were conducted at irrigation pressures (50-150 cmH0) and five different outflow resistance scenarios simulated with catheters of different lengths and diameters. P was measured with a fiber optic pressure sensor positioned in the renal pelvis. Flowrate was determined by measuring the mass of drainage fluid over 60 s. P was lower with the m-ureteroscope than the s-ureteroscope when equivalent flowrates were delivered (i.e. 34 vs. 82 cmH0 respectively with 15 ml/min irrigation in a high outflow resistance scenario). Flowrate was higher with the m-ureteroscope than the s-ureteroscope when equivalent irrigation pressures were applied (i.e. 28 vs. 14 ml/min respectively with irrigation pressure 150 cmH0 in a high outflow resistance scenario). The m-ureteroscope has improved pressure-flow dynamics imparting important clinical benefits. More importantly, this approach to framing ureteroscopy in the context of pressure-flow relationships related by resistance values allows quantification of ureteroscopy within a deterministic system, which can be used to streamline future device development and technological innovation.