Suction mini-percutaneous nephrolithotomy versus standard percutaneous nephrolithotomy for the management of 2–4 cm kidney stones: study protocol for an international, multicenter, parallel-group, noninferiority, randomized controlled trial

Purpose: Percutaneous nephrolithotomy (PCNL) is recommended as the first-line treatment choice for the management of kidney stones larger than 2 cm. However, tract-related complications have always been a concern, especially in standard PCNL where a larger tract > 24Fr is established. The mini-PCNL technique with smaller tract (≤ 18 Fr) has been introduced to decrease tract related complications. Yet, with a smaller mini-PCNL tract, fragments must be fragmented into smaller pieces before extraction, potentially prolonging the operative time. Moreover, if the outflow of irrigation fluid is insufficient via the smaller tract, the intrarenal pressure (IRP) can build up, leading to pyelovenous backflow and infectious complications - an issue theoretically mitigated by the addition of suction techniques. However, high-level evidence comparing suction mini-PCNL outcomes to standard PCNL is still lacking. Methods: The present multicenter, international, randomized controlled noninferiority trial compares suction mini-PCNL to standard PCNL in the management of 2-4 cm kidney stones. The primary outcomes are the immediate postoperative stone-free rate (SFR) and operative time, while secondary outcomes include the final SFR at 1 month, postoperative pain score, length of hospital stay, postoperative complications, and quality of life. Results: A total of 960 patients from 20 urological centers will be randomized to receive either suction mini-PCNL or standard PCNL. Intention-to-treat analysis will be performed. For SFR, non-inferiority will be concluded if the lower bound of the 95% confidence interval for the absolute risk difference exceeds - 10%. For operative time, non-inferiority will be concluded if the lower bound of the 95% confidence interval for the mean difference exceeds - 10 min. For all other analyses, a two-sided p-value of < 0.05 will be regarded as statistically significant. Subgroup analyses will be performed to explore potential effect modification by stone location and stone density. Conclusion: The aim of this trial is to generate high-level evidence regarding the noninferiority of suction mini-PCNL compared to standard PCNL for 2-4 cm renal stones. The trial is registered on ClinicalTrials.gov as NCT05088213.