A “stepped” flexible vacuum-assisted ureteral access sheath improves stone clearance efficiency: experimental results from an ex vivo porcine model

Objective To evaluate the impact of a novel “stepped” flexible vacuum-assisted ureteral access sheath (SFV-UAS) on stone clearance efficiency during flexible ureteroscopy lithotripsy (f-URL). Methods Human upper urinary tract stone fragments (< 4 mm) were placed into ex vivo porcine renal pelves. We simulated f-URL stone extraction under continuous irrigation and vacuum suction, comparing the SFV-UAS (ureteral segment 12/14 Fr, cystourethral segment 16/18 Fr) with a conventional flexible vacuum-assisted ureteral access sheath (FV-UAS)(12/14 Fr). With intrarenal pressure strictly controlled (< 30 mmHg) and constant vacuum suction (01 step), irrigation flow rates were evaluated at 40 mL/min, 50 mL/min, 60 mL/min, 70 mL/min, 80 mL/min, and 90 mL/min. Stone evacuation times were recorded. Results (1) Sheath type and irrigation flow rate exhibited significant main effects on clearance time [F(1,408) = 189.231, P < 0.01, effect size 31.7%; and F(5,408) = 38.721, P < 0.01, effect size 32.2%, respectively]. A significant two-way interaction was also observed [F(5,408) = 8.372, P < 0.01, effect size 9.3%]. (2) Simple main effects revealed: First, across all corresponding irrigation rates, the SFV-UAS group achieved significantly shorter clearance times than the FV-UAS group (mean differences: MD = −21.598, −18.099, −8.172, −11.129, −9.762, −4.883; all P < 0.05). Second, within the SFV-UAS group, rates ≥ 70 mL/min resulted in significantly shorter clearance times vs. the 40 mL/min baseline (mean differences:MD = −9.393, −9.771, −9.084; all P < 0.05). Although comparisons between 60 mL/min and higher rates were non-significant, 70 mL/min was the lowest evaluated irrigation rate that demonstrated a statistically significant reduction in clearance time compared to the 40 mL/min baseline. Third, within the FV-UAS group, clearance times at ≥ 60 mL/min were significantly shorter than at 40 and 50 mL/min (mean differences:MD = −19.664, −12.370; all P < 0.001), with no significant differences among the ≥ 60 mL/min groups, indicating its plateau at ≥ 60 mL/min. Conclusion Within the parameters of this ex vivo model,the SFV-UAS significantly reduces the measured stone clearance time during f-URL compared to the FV-UAS under identical irrigation conditions. For the SFV-UAS group, targeting an irrigation flow rate of ≥ 70 mL/min consistently optimizes stone extraction efficiency relative to baseline conditions.