7.5F Mini Flexible Ureteroscope in Retrograde Intrarenal Surgery: Initial Results from a Multicenter Randomized Clinical Trial.

To report the initial results of an randomized clinical trail comparing the safety and efficacy between 7.5F and 9.2F flexible ureteroscope (FUS) in the management of renal calculi <2 cm. Eighty patients were enrolled and received retrograde intrarenal surgery (RIRS) with a different size FUS. The operation results and complications were compared. Two cases in the 7.5F group and four cases in the 9.2F group failed to insert the 12/14F ureteral access sheath (UAS), respectively, and no significant difference ( = 0.396) was noted. However, 10/12F UAS was inserted in the 7.5F group, but not available in the 9.2F group, and thus, the 10/12F UAS inserting rate in the 7.5F group was higher than in the 9.2F group (100% 0%,  = 0.014), and the UAS insertion failure rate in 9.2F group was higher than in the 7.5F group (10% 0%,  = 0.040). The operation time in 7.5F group was shorter than the 9.2F group (35.60 ± 7.86 41.05 ± 8.14,  = 0.003). Less irrigation was required in 7.5F group (813.93 ± 279.47 mL 1504.18 ± 385.31 mL,  = 0.000). The postoperative fever rate in 9.2F group was higher than 7.5F group (20% 5%,  = 0.043). There was no significant difference in sepsis (0% 2.5%,  = 0.314) between the two groups. No significant difference was noted in hospital stay (0.93 ± 0.49 days 1.14 ± 0.64 days,  = 0.099) between the two groups. The final stone-free rate (SFR) in 7.5F group was higher than 9.2F group (95% 80%,  = 0.043). The latest 7.5F mini FUS was a reliable instrument in RIRS to keep a good visualization with low requirement of irrigation, low postoperative infection complication, and also a high SFR when compared with the conventional 9.2F FUS. NCT05231577.