Characterisation of vent designs in flexible and navigable suction ureteric access sheaths.

OBJECTIVES: To evaluate the different vent designs in three commercially available flexible and navigable suction (FANS) access sheaths-ClearPetra® (Well lead, Guangzhou, China), Elephant II (YIGAOMedical, Hangzhou, China) and Tuohy-Borst FANS access sheath (Seplou, Zhejiang, China)-and quantify the effects these differing designs have on the control of suction. METHODS: We conducted benchtop experiments to quantify the effect of pressure vent design on suction pressure control. Suction experiments were conducted both in an atmospheric beaker and in a phantom kidney model. With an indwelling 9.5-F LithoVue™ (Boston Scientific, Marlborough, MA, USA) ureteroscope, constant suction was applied to the access sheath's suction port. The vents were incrementally closed and corresponding flow rates calculated as a proxy for suction pressure. A mathematical model was developed to predict the impact of pressure control vent design on suction pressure control, flow rates and intrarenal pressure. RESULTS: For both the ClearPetra and Elephant II suction access sheaths, opening the length of the vent has an exponential reduction in suction pressure. Negligible suction is exerted on the renal pelvis with ≥3 mm of vent open. The Seplou suction access sheath has a Tuohy-Borst pressure vent, which allows finer control of suction pressures. The mathematical model showed strong agreement with experimental data. CONCLUSION: Commercially available FANS access sheaths are similar in most aspects but have differing vent designs. With the vents open no suction is exerted on the renal collecting system. However, because the flexible access sheath intrarenal end is within the renal pelvis, outflow resistance is low and the pelvis will deflate, giving the impression of suction. We have developed a mathematical model that predicts flow at different suction pressures and with different degrees of the pressure vents open. This allows simulations across multidimensional parameter spaces and the resulting quantitative predictions can be exploited to assess the implications of FANS access sheath and ureteroscope design.