Clinical study of intraoperative real-time measurement in predicting successful removal of stone fragments during retrograde intra-renal surgery

Abstract Purpose To investigate the application value of intraoperative real-time measurement in retrograde intra-renal surgery (RIRS), and to analyze the clinical characteristics of perioperative stones and the factors affecting the efficient removal of stone fragments. Methods In RIRS a total of 67 extraction procedures of stones were retrospectively analyzed. Flexible ureteroscopy with 8.4F URF P-5 (Olympus, Tokyo, Japan) and UAS with F12/14 navigator HD (Boston Scientific, Natick, Ma, USA) were employed intraoperatively. Judge the region of stone fragments in the field of vision, which is divided into the region within 1/3 of the diameter, 1/3 to 1/2, 1/2 to 2/3 and more than 2/3. Record whether the stone fragments can be removed through UAS. The size of stone fragments was determined by the electronic caliper. Analyze the surgical video images, and measure the relative endoscopic horizontal size (REHS) and the relative endoscopic maximum size (REMS) of stones and record whether the stone fragments can be removed through UAS. Results All operations were successful, and 67 extraction procedures of stones were performed, with 48 cases in the passable group and 19 cases in the non-passing group. The success rate of stone fragments removal in each region was 93.3% in 1/3 region, 86.8% in 1/3 to 1/2 region, 8.3% in 1/2 to 2/3 region and 0% in more than 2/3 region. That is, 88.7% of the stones located in 1/2 region were successfully removed. Comparing the receiver operating characteristic curve (ROC curve) of REHS and REMS, the area under the curve (AUC) of REHS was 0.895 (95% CI: 0.796–0.956), and the AUC of REMS was 0.797 (95% CI: 0.681–0.885); The difference of AUC between the two methods was 0.0981, the Z-statistic was 1.137, P = 0.02555, and the predictive value of REHS was higher than that of REMS. And then the ROC curve of REHS was analyzed. The maximum cutoff value was 0.47, AUC is 0.895 (sensitivity 78.9% and specificity 89.6%). According to the clinical application value of real-time intraoperative measurement, 0.50 was selected as the actual cutoff value, with the AUC 0.811, P < 0.0001 (sensitivity 68.4% and specificity 93.7%). According to the REHSS cutoff value of 0.5 (namely "one-half principle"), the factors that prevent stones from being removed include irregular stone shape, irregular grasping of stones by the stone basket, poor position of the ureteral channel sheath, and hard stone texture and so on. Conclusion When the stone basket is utilized for real-time measurement during flexible ureteroscopy, it is possible to determine efficiently and reliably that stone fragments are removed through UAS with the REHS maximum cutoff value of 0.5, namely "one-half principle". This approach of prediction is anticipated to increase operation effectiveness, shorten operation duration, and increase stone removal rate.