In-depth exploration and initial clinical practice of the ratio of endoscope-sheath diameter theory: smaller flexible ureteroscope with smaller ureteral access sheath.

Objectives: To assess the outcomes of combining a 7.5Fr flexible ureteroscope (fURS) with a 10/12F ureteral access sheath (UAS) through a comprehensive in vitro and in vivo evalu-ation.

Methods: We conducted a comparative analysis, evaluating the impact of a 7.5Fr fURS in contrast to others on in trapelvic pressure (IPP) and perfusion fluid flow rate (PFFR) in vitro. This assessµent involved varying ratios of endoscope-sheath diaµeter (RESDs). Subsequently, we prospectively enrolled 23 patients with renal calculi <2 cm who underwent laser lithotripsy using the coµbination of a 7.5Fr fURS and a 10/12F UAS. The patients' profiles, including preoperative, operative inforµation and postoperative coµplications, were recorded.

Results: In vitro experi-ments revealed that IPP and PFFR remained optimal when the RESDs were ≤ 0.75. Notably, only the 7.5Fr fURS ensured a safe IPP when combined with a 10/12F UAS. In clinical research, the sheath placement success rate was 100%, with an average operation time of 55.0 ± 20.0 min and a lithotripsy time of 150.4 ± 199.0 s. Mild ureteral injury necessitated the retention of a double-J stent in five cases for a month. The hospitalization duration and 24-h pain score averaged 45.6 ± 15.5 h and 4.3 ± 3.5, respectively. The one-month stone-free rate was 91.3%. Regarding stent-related symptoms, the overactive bladder symptom score averaged 1.7 ± 1.5, the international prostate symptom score was 3.3 ± 2.8, and the quality of life was 1.3 ± 1.7.

Conclusions: Combining a 7.5Fr fURS with a 10/12Fr UAS is recommended as a secure option for treating renal calculi < 2 cm. Postoperative pain management is a future concern.