Physical characteristics of next-generation ureteral access sheaths: buckling and kinking.

Objective: To evaluate physical characteristics of next-generation access sheaths that impact clinical failure.

Methods: Testing of the Cook Flexor (12/14 Fr x 35 cm, Cook), ACMI UroPass (12/14 Fr x 38 cm, ACMI), Bard Aquaguide (11/13 Fr x 35 cm Bard), and Boston Scientific Navigator (11/13 Fr x 36 cm BSCI-11, 13/15 Fr x 36 cm BSCI-13) was performed on a linear motion stage driven by a stepper motor with a resolution of 5 microm per step. Force was measured at a sampling rate of 5 Hz with a Wagner FDIX digital force gauge. Friction force was measured by pulling sheaths at 2.5 mm/s through 2.78 mm (8.3 Fr) holes drilled in 36 mm thick biologic material. Buckling force was measured as the force required to compress a 25-cm length of sheath in a clamp-clamp configuration during a 30 mm move. Kinking was measured as the slope of the force-deflection curve for wall compression over a deflection of 2 mm.

Results: No significant difference was noted in the friction force of the Cook (1.2 N), Bard (1.3 N), BSCI-11 (1.0 N), and BSCI-13 (1.0 N). Buckling force was significantly greater for the Cook (5.1 +/- 0.49 N) than the Bard (2.8 +/- 0.31 N), BSCI-11 (2.0 +/- 0.25 N), ACMI (3.2 +/- 0.33 N), and BSCI-13 (2.9 +/- 0.31 N). Kinking force was significantly lower with the Bard (9 N/mm) than the Cook (42 N/mm), BSCI-11 (41 N/mm), and BSCI-13 (30 N/mm), and significantly higher with the ACMI (83 N/mm).

Conclusions: The Cook Flexor sheath is most resistant to buckling forces that would predict failure to advance up the ureter. The Bard Aquaglide is most likely to kink after removal of the inner obturator, whereas the ACMI Uropass is most resistant to kinking.