Feasibility and safety of 6.3 Fr vs. 7.5 Fr digital disposable ureteroscopes in retrograde intrarenal surgery: a prospective randomised trial.

Abstract

Introduction: Flexible ureterorenoscopy has become one of the cornerstones of minimally invasive treatment for nephrolithiasis. One of the most critical variables in scope design is the outer diameter, improving accessibility. Recently introduced 6.3 Fr ultra-slim digital ureteroscopes may offer clinical advantages over bigger scopes, but there is no data on their performance.

Objectives: This study aimed to prospectively compare the feasibility, safety, durability, and procedural outcomes of RIRS performed using 6.3 Fr and 7.5 Fr digital disposable ureteroscopes from the same manufacturer, evaluating intraoperative parameters, image quality, access rates, and early postoperative results.

Material and methods: Thirty adult patients with renal stones < 1.5 cm or cumulative volume < 850 mm³ were enrolled in a single-centre, randomised, prospective trial. All procedures were performed by a single experienced urologist using CE-certified digital disposable ureteroscopes. Lithotripsy was conducted with a high-power holmium laser and a 272-micron fiber. Subjective evaluations of manoeuvrability and image quality were recorded using 5-point Likert scales. Operator workload was assessed with NASA Task Load Index. In-vitro deflection range and image quality were measured before and after clinical use. Postoperative outcomes, complications, and intraoperative stone-free rates were recorded.

Results: Baseline characteristics were comparable between groups not showing major differences. Ureteral access sheaths were used in 47% of cases. Endoscope insertion into the kidney was successful in all patients. Lithotripsy was complete in 87% of cases using the 6.3 Fr scope and 73% with the 7.5 Fr scope. No statistically significant differences were found in image quality or manoeuvrability scores. Both devices allowed access to the lower pole with and without a working channel instrument. No intraoperative device failures occurred, and postoperative deflection loss was minor and infrequent. One patient required prolonged hospitalisation due to infection while all remaining patients were discharged within 24 h. No ureteral injuries or complications exceeding Clavien-Dindo grade II were observed.

Conclusions: The results of this study indicate that the 6.3 Fr ultra-slim ureteroscope is a feasible and safe alternative to the bigger 7.5 Fr model, with no compromise in visualisation, manoeuvrability, or device integrity. Given its comparable performance and potential for reduced ureteral trauma, the ultra-slim scope may serve as a valuable tool in modern endourology.