Access Sheaths With Aspiration for Renal RetrOgrade Surgery, Randomized CompArative Outcomes

The goal of this clinical trial is to learn whether the ClearPetra ureteral access sheath (Coloplast) is more effective than the Navigator ureteral access sheath (Boston Scientific) in treating intrarenal kidney stones of 1-3 cm in adult patients undergoing flexible ureteroscopy (RIRS). The main questions it aims to answer are: Does ClearPetra achieve a higher stone-free rate at 1 month post-intervention compared to Navigator, as assessed by non-contrast abdominal-pelvic CT scan? Does ClearPetra reduce total surgical time compared to Navigator? Does ClearPetra lower the retreatment rate at 3 months compared to Navigator? Does ClearPetra present a rate of clinically significant complications (Clavien-Dindo ≥ II) that is lower than or similar to Navigator? Researchers will compare flexible ureteroscopy using the ClearPetra vacuum-assisted flexible ureteral access sheath to flexible ureteroscopy using the Navigator standard rigid ureteral access sheath, to see if ClearPetra leads to higher stone clearance rates while maintaining a comparable safety profile. Participants will: Undergo flexible ureteroscopy (RIRS) using one of two randomly assigned ureteral access sheaths (ClearPetra or Navigator), determined by computer-generated randomization immediately before surgery Have a non-contrast abdominal-pelvic CT scan at 1 month post-intervention to assess stone-free status Have a non-contrast abdominal-pelvic CT scan at 3 months post-intervention to evaluate residual fragments and the need for retreatment Attend follow-up visits at 1 month and 3 months post-surgery for clinical assessment and complication recording The study will be conducted at the Urology Department of Hospital Universitario Virgen del Rocío (Seville, Spain), a tertiary reference centre. A total of 156 patients will be randomized in a 1:1 ratio (78 per group), with pre-defined subgroup analyses stratified by stone size (1-2 cm vs. \>2 cm). The outcome assessor evaluating CT images for stone-fr