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

Understanding renal pelvis pressure (P_RP) during ureteroscopy (URS) has become increasingly important. High irrigation rates, desirable to maintain visualization and limit thermal dose, can increase P_RP. Use of a multi-channel ureteroscope (m-ureteroscope) with a dedicated drainage channel is one strategy that may facilitate simultaneous low P_RP and high flowrate. We sought to define the relationship between P_RP 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 cmH₂0) and five different outflow resistance scenarios simulated with catheters of different lengths and diameters. P_RP 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_RP was lower with the m-ureteroscope than the s-ureteroscope when equivalent flowrates were delivered (i.e. 34 vs. 82 cmH₂0 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 cmH₂0 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.