Advancement speed and sheath caliber influence peak axial insertion force and ureteral injury during ureteral access sheath placement: an ex vivo porcine study.

To evaluate the effects of ureteral access sheath (UAS) caliber and manually applied target advancement speed on peak axial insertion force and visible ureteral injury in an ex vivo porcine repeated-measures model. Bilateral kidney-ureter specimens from 15 pigs yielded 30 ureters. Ureters were allocated by calculator-generated random numbers to 10/12, 11/13, or 12/14 Fr UAS groups (10 ureters per caliber). Each ureter underwent three insertions, one under each target-speed condition (0.5, 1.0, and 2.0 cm/s), in randomized order, yielding 90 force measurements. Specimens were stored in normal saline at 4°C and tested within 6 h. Peak force was analyzed using a mixed repeated-measures factorial model. Visible injury was graded by three blinded senior urologists using the Post-Ureteroscopic Lesion Scale (PULS).UAS caliber (F[2,27]=38.49, P<0.001), target speed (F[2,54]=66.36, P<0.001), and the caliber × target-speed interaction (F[4,54]=8.31, P<0.001) significantly influenced peak force. Median force increased from 3.35 (IQR 2.24-3.40) N at 0.5 cm/s to 6.39 (5.85-6.76) N at 2.0 cm/s for 10/12 Fr UASs and from 4.87 (4.06-5.28) N to 7.24 (6.53-7.36) N for 11/13 Fr UASs; the speed effect was attenuated for 12/14 Fr UASs. Visible injury occurred in 0/30 (0%), 4/30 (13.3%), and 7/30 (23.3%) observations at 0.5, 1.0, and 2.0 cm/s, respectively (Cochran Q P=0.035). The 0.5 versus 2.0 cm/s paired comparison was significant after Holm adjustment (P=0.047). In exploratory generalized estimating equations, peak force was associated with visible injury (odds ratio per 1 N, 1.62; 95% CI 1.08-2.41; P=0.019), although the model was unadjusted and force distributions overlapped.UAS caliber, target advancement speed, and their interaction influenced peak insertion force. Visible injury increased across target-speed conditions, but a single peak-force value did not define a universal injury threshold. Slow, controlled advancement and use of the smallest clinically appropriate UAS remain prudent.