Intelligent versus Flexible Negative-Pressure Aspiration Sheath for Ureteroscopic Lithotripsy: A Single-Center Retrospective Study with Systematic Review and Meta-Analysis

Background: Negative-pressure aspiration ureteral access sheaths (NP-UAS) outperform traditional sheaths in retrograde intrarenal surgery (RIRS), but whether the two designs — the intelligent pressure-controlled type (real-time intrarenal pressure monitoring) and the flexible negative-pressure type (steerable tip) — differ in clinical outcomes is unknown. Three head-to-head comparisons exist, all using clinically insignificant residual fragment (CIRF)-based stone-free rate (SFR) definitions, with no systematic synthesis. This study aimed to determine whether the two designs differ in clinically relevant outcomes after RIRS.

Methods: This study combined a single-center retrospective cohort (264 patients; 147 intelligent, 117 flexible NP-UAS) with a meta-analysis of all published head-to-head comparisons (4 studies, 539 patients). The primary outcome was SFR, defined as zero residual fragments on 1-mm computed tomography (CT) within 48 hours to maximize sensitivity to between-group differences. Confounding by indication was addressed with multivariable regression, propensity score matching (PSM), inverse probability of treatment weighting (IPTW), Firth penalized likelihood, and E-value analysis; the meta-analysis used a restricted maximum likelihood (REML) random-effects model. Certainty was graded using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

Results: Crude SFR was 24.5% (intelligent) versus 14.5% (flexible) (odds ratio (OR) 1.91, 95% confidence interval (CI) 1.02–3.68, p=0.047), attenuating to non-significance after sequential adjustment (operative time excluded: OR 1.72, 95% CI 0.83–3.68, p=0.154), with consistent results across PSM (OR 1.67), IPTW (OR 1.49), and Firth regression (OR 1.65); E-values were 3.23 (crude) and 2.83 (adjusted). Operative time was shorter with the flexible sheath (crude −25.9 min), but mediation analysis showed it did not mediate the sheath–SFR relationship (average causal mediation effect (ACME) p=0.302). Postoperative infection did not differ between groups. In the exploratory meta-analysis, subgrouping by SFR definition reduced I² from 75.7% to 0.7%, though confounded with study center. GRADE certainty was very low for all outcomes.

Conclusions: Across five analytical methods and meta-analysis, the evidence is insufficient to establish a clinically meaningful SFR difference between intelligent and flexible NP-UAS. The flexible sheath is associated with shorter operative time, but without differential stone clearance, and GRADE certainty is very low. A non-inferiority randomized controlled trial (RCT) (approximately 500 patients) with standardized zero-fragment CT SFR is required.