Cumulative Sum Analysis for Experiences of a Single-Session Retrograde Intrarenal Stone Surgery and Analysis of Predictors for Stone-Free Status

Sung Yong Cho,Chang Wook Jeong,Jae Hyun Jung,Min Soo Choo,Seung Bae Lee,Hwancheol Son,Sohee Oh,Hyeon Jeong,Anthony Wi Lo

doi:10.1371/journal.pone.0084878

Abstract

IntroductionThis study investigated the learning curve of a single-session retrograde intrarenal surgery (RIRS) in patients with mid-sized stones. Competence and trainee proficiency for RIRS was assessed using cumulative sum analysis (CUSUM).Materials and MethodsThe study design and the use of patients' information stored in the hospital database were approved by the Institutional Review Board of our institution. A retrospective review was performed for 100 patients who underwent a single-session RIRS. Patients were included if the main stone had a maximal diameter between 10 and 30 mm. The presence of a residual stone was checked on postoperative day 1 and at one-month follow-up visit. Fragmentation efficacy was calculated “removed stone volume (mm3) divided by operative time (min)”. CUSUM analysis was used for monitoring change in fragmentation efficacy, and we tested whether or not acceptable surgical outcomes were achieved.ResultsThe mean age was 54.7±14.8 years. Serum creatinine level did not change significantly. Estimated GFR and hemoglobin were within normal limits postoperatively. The CUSUM curve tended to be flat until the 25th case and showed a rising pattern but declined again until the 56th case. After that point, the fragmentation efficacy reached a plateau. The acceptable level of fragmentation efficacy was 25 ml/min. Multivariate logistic regression analyses showed that stone-free rate was significantly lower for cases with multiple stones than those with a single stone (OR = 0.147, CI 0.032 – 0.674, P value = 0.005) and for cases with higher number of sites (OR = 0.676, CI 0.517 – 0.882, P value = 0.004).ConclusionsThe statistical analysis of RIRS learning experience revealed that 56 cases were required for reaching a plateau in the learning curve. The number of stones and the number of sites were significant predictors for stone-free status.

Highlights

This study investigated the learning curve of a single-session retrograde intrarenal surgery (RIRS) in patients with mid-sized stones
Multivariate logistic regression analyses showed that stone-free rate was significantly lower for cases with multiple stones than those with a single stone (OR = 0.147, CI 0.032 – 0.674, P value = 0.005) and for cases with higher number of sites (OR = 0.676, CI 0.517 – 0.882, P value = 0.004)
The statistical analysis of RIRS learning experience revealed that 56 cases were required for reaching a plateau in the learning curve

Summary

Introduction

This study investigated the learning curve of a single-session retrograde intrarenal surgery (RIRS) in patients with mid-sized stones. RIRS has shown a high SFR comparable to that of PNL, and offers the possibility of less renal injury than PNL because this procedure does not penetrate the renal cortex [7]. Few studies have reported cases in which RIRS was able to retrieve stones up to 3 cm in size, depending on the skill level of the operating surgeon [3,10]. Considering these factors, RIRS appears to be a good option for mid-sized stones with diameters between 10 and 30 mm at high-volume centers. In order to adopt RIRS, endeavors to overcome the surgical difficulties would be important, especially for the less-experienced trainees in the urologic field; few investigations have shown the learning curve to acquire the appropriate surgical proficiency for RIRS

Methods

Results

Conclusion