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Development of a Novel Metric to Preoperatively Estimate Flexible Ureteroscopy Operative Time: “The Stone Treatment Scale (STS)”
David W. Sobel, MD, Timothy O'Rourke, MD, Rebecca Ortiz, BA, Nicole Thomasian, BS, Philip Caffery, PhD, Christopher Tucci, MS, Gyan Pareek, MD.
Brown University, Providence, RI.

Background: As operating room (OR) time is a fixed commodity, new methods are needed to improve the accuracy of room time estimates to mitigate underutilization. We sought to develop a surgeon-friendly metric for flexible ureteroscopy and laser lithotripsy (URSLL) similar to prostate ablation rates by which urologists can better estimate case time for improved perioperative planning.
Methods: A retrospective review of all flexible URSLL procedures of calcium oxalate (CaOx) stones performed from December 2016 to April 2018 performed by 11 urologists at an academic institution was conducted. Patient characteristics, imaging, operative times, and outcomes were analyzed. Cases were included if preoperative computed tomography (CT) imaging was available and the patient was rendered stone free either by postoperative imaging or intraoperative surgeon interpretation. All cases were performed with a Lumenis Pulse 30H laser unit and dusting technique. Procedure length was measured by case start-to-case completion times. A novel measure of stone treatment efficiency was calculated for each case as stone burden treated (millimeter/operative time [minutes]). Differences between urologists were assessed through one-way analysis of variance (ANOVA).
Results: 69 CaOx flexible URSLL procedures were reviewed. 37 (54%) of patients were female; 60 (86%) of patients had postoperative imaging demonstrating stone-free status and 35 (51%) patients were declared visually stone free at completion of the case. The mean stone size was 9.2 mm (R 3-24, SD 4.53) and the mean operative time was 42 minutes (R 9-158, SD 27.7). The mean STES amongst all urologists studied was 0.3 mm/minute (R 0.38-1.33 SD 0.19) (Table 1). A significant difference between urologists was identified utilizing this novel metric of efficiency [F(10,58) = 3.758, p=.006] (Figure 1). The most efficient mean urologist STS in this series was 0.60 mm/minute and the least was 0.16.
Conclusions: The Stone Treatment Score (STS) can be a valuable metric for determining a urologist's efficiency to completely clear stone ureteroscopically within a set of technological constraints (laser power, technique). Operative scheduling may allow for more cases per operative day based on the efficiency a surgeon can achieve. This metric may be used to compare surgeon performance as well as create opportunities to improve perioperative planning and operating room utilization. The most efficient urologist by this metric in our study was a fellowship-trained endourologist. Further investigation as to factors associated with efficiency in the STS including assistant (resident or fellow) training year and experience. Further study to validate this metric against other operative efficiency estimates is warranted.

Descriptive Statistics
N = 69 proceduresMeanRangeStandard Deviation
Age (years)58.031.27-82.2913.38
Stone size (mm)9.23-244.53
Procedure time (min)42.49-15827.74
Stone Treatment Score (STS) (mm/min)0.30.04-1.330.20


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