Purpose: Our aim was to determine the optimal size of access sheath for ureteroscopy and stone lasertripsy to achieve good irrigant flow while maintaining the lowest possible intrarenal pressure.
Materials and methods: We used an in vitro anatomic model into which a pressure transducer was incorporated. Cook Peel-Away 10F, Flexor 12F, 14F, 16F single lumen, and a new 14F Flexor dual-lumen sheath were tested. Irrigant flow and intrarenal pressure were measured with an empty ureteroscope working channel and with a 1.4F or 2.4F basket within the working channel with a hydrostatic pressure of 1 m and 2 m, respectively. For the dual-lumen sheath, the irrigation was either connected to the scope or the second channel of the access sheath. Two other configurations were tested: 4F ureteral catheter placed alongside a 10F sheath (configuration 1) or a 5F ureteral catheter within a 16F access sheath (configuration 2).
Results: With an empty working channel, irrigant flow increased with sheath diameter. The presence of a 1.4F or 2.4F basket, however, reduced flow up to 65% and 90%, respectively. Increasing the hydrostatic column to 2 m height improved the irrigant flow but with a predisposition to a higher intrarenal pressure. Using configurations 1 and 2, the flow rates improved by 250% and 700%, respectively, with a 2.4F basket in the working channel, and could also be used with a 2 m hydrostatic column without raising the intrarenal pressure.
Conclusions: Increased access sheath diameter does not improve flow when the working channel of a flexible ureteroscope is occupied. Our proposed configuration of a ureteral access catheter placed inside or alongside the access sheath provides by far the highest flow rates without a rise in the intrarenal pressure.