Effects of a head-up position on stone retrieval efficiency and intrarenal pressure using a flexible navigable suction access sheath: an in vitro study.

Although flexible navigable suction ureteral access sheaths (FANS) combined with head-up positioning has shown promise in retrograde intrarenal surgery, the effects of the head-up position during the stone retrieval phase have yet to be quantified. In this study, we evaluated the effects of a 20° head-up position on stone retrieval time and intrarenal pressure (IRP) using FANS in a kidney phantom model. Using a supramolecular hydrogel kidney phantom, we performed 44 trials (22 paired comparisons). Five artificial stone fragments (2-3 mm) were placed in the renal pelvis and retrieved via suction through an 11/13-Fr FANS under continuous gravity-driven irrigation. Trials alternated between supine (Group A, 0°) and head-up (Group B, + 20°) positions. IRP was measured using a pressure sensor inserted into the upper calyx. The primary outcome was stone retrieval time, whereas mean and peak IRPs were secondary outcomes. All fragments were retrieved by suction alone without the use of a basket. Mean stone retrieval time was significantly shorter in Group B than in Group A (167.4 ± 44.5 vs. 223.0 ± 65.6 s, respectively; mean difference - 55.7 s; 95% confidence interval, - 92.1 to - 19.3; p < 0.01). Mean IRP was significantly lower in Group B (- 1.40 ± 2.34 vs. 0.51 ± 2.70 mmHg; p < 0.01), as was the peak IRP (2.40 ± 2.66 vs. 7.57 ± 3.56 mmHg; p < 0.01). Our findings provide experimental evidence supporting the integration of positional optimization in FANS-assisted retrograde intrarenal surgery.