Flexible and navigable suction access sheaths: balancing sheath and scope size for desired flows.

OBJECTIVE To study the effects of ureteroscope diameter, 'flexible and navigable suction' access sheaths (FANS) diameter, and irrigation pressure on intrarenal pressure (IRP) and irrigation fluid flow rates in ex vivo porcine kidneys; these benchtop data were compared against mathematical modelling results. MATERIALS AND METHODS Fresh ex vivo porcine kidneys and ureters were used. The tip of an 11/13- or 10/12-F ClearPetra® FANS was placed within the renal pelvis. Either a 9.5-F Boston Scientific LithoVue™, 7.5-F PUSEN PU3033, or 6.3-F HugeMed HU30M ureteroscope was inserted through the sheath. Irrigation pressures of 0, 50, 100, 150 and 200 mmHg were applied. No suction was applied. The corresponding steady state IRP and flow rate was recorded. This was replicated in three separate porcine kidneys. Benchtop data were compared to mathematical model predictions. The maximum flow rates that could be achieved with an IRP ≤30 mmHg were extrapolated. RESULTS The FANS and ureteroscope geometries affect outflow resistance. Lower outflow resistances, allow higher irrigation pressures and flow rates to be used whilst maintaining an IRP ≤30 mmHg (without suction). Whilst keeping IRP ≤30 mmHg with an 11/13-F FANS: ~700 mmHg irrigation (~120 mL/min) could be used with a 6.3-F ureteroscope; ~300 mmHg irrigation (flow rate ~65 mL/min) could be used with a 7.5-F ureteroscope; ~100 mmHg irrigation (~15 mL/min) could be used with a 9.5-F ureteroscope. CONCLUSIONS Using a FANS in the renal pelvis potentially allows for higher irrigation pressures whilst maintaining a low IRP (without the need for suction). With intraoperative monitoring of IRP, irrigation pressure could be increased to achieve flow rates up to 24 times higher than those achievable with gravity irrigation (120 vs ~5 mL/min).