Development and internal validation of a nomogram for predicting stone-free status after flexible ureteroscopy for renal stones

Clinical Nomograms to Predict Stone-Free Rates after Shock-Wave Lithotripsy: Development and Internal-Validation

PURPOSE

Shock-wave lithotripsy (SWL) is accepted as the first line treatment modality for uncomplicated upper urinary tract stones; however, validated prediction models with regards to stone-free rates (SFRs) are still needed. We aimed to develop nomograms predicting SFRs after the first and within the third session of SWL. Computed tomography (CT) information was also modeled for constructing nomograms.

MATERIALS AND METHODS

From March 2006 to December 2013, 3028 patients were treated with SWL for ureter and renal stones at our three tertiary institutions. Four cohorts were constructed: Total-development, Total-validation, CT-development, and CT-validation cohorts. The nomograms were developed using multivariate logistic regression models with selected significant variables in a univariate logistic regression model. A C-index was used to assess the discrimination accuracy of nomograms and calibration plots were used to analyze the consistency of prediction.

RESULTS

The SFR, after the first and within the third session, was 48.3% and 68.8%, respectively. Significant variables were sex, stone location, stone number, and maximal stone diameter in the Total-development cohort, and mean Hounsfield unit (HU) and grade of hydronephrosis (HN) were additional parameters in the CT-development cohort. The C-indices were 0.712 and 0.723 for after the first and within the third session of SWL in the Total-development cohort, and 0.755 and 0.756, in the CT-development cohort, respectively. The calibration plots showed good correspondences.

CONCLUSIONS

We constructed and validated nomograms to predict SFR after SWL. To the best of our knowledge, these are the first graphical nomograms to be modeled with CT information. These may be useful for patient counseling and treatment decision-making.

Clinical factors prolonging the operative time of flexible ureteroscopy for renal stones: a single-center analysis

The objective of the study was to evaluate the clinical factors affecting the operative time of flexible ureteroscopy (fURS). We retrospectively evaluated 233 patients with renal stones who had been treated successfully and had stone-free status 3 months after fURS and holmium laser lithotripsy between December 2009 and December 2013 at a single institute. Operative time was divided into three periods (total, before fragmentation, and after starting fragmentation), and associations between possible factors and these periods were analyzed by a multivariate logistic regression model with backward selection. The mean total operative time was 74.0 ± 32.0 min. There were significant differences in the following clinical factors: sex, body height, stone volume, maximum and mean Hounsfield units (HUs), diameter of the ureteral access sheath, and experience of the surgeon, between patients who underwent procedures with a total operative time of less or more than 90 min. A multivariate assessment revealed four independent factors influencing total operative time (P < 0.05): stone volume (P < 0.001), experience of the surgeon (P < 0.001), maximum HUs (P = 0.014), and lack of preoperative stenting (P = 0.027). Larger stone volume, lower experience level of the surgeon, higher HUs, and the absence of preoperative stenting were identified as parameters prolonging the total operative time of fURS and, in particular, the operative time after starting fragmentation. On the other hand, operative time before starting fragmentation, which represented the time required to identify the stone by ureteroscopy and insert the access sheath, was more difficult to predict preoperatively.