Impact of Renal Access Angle and Speed of Nephroscope Retrieval Movements on the Vortex Effect.

OBJECTIVE: To analyze the influence of different renal access angles (AAs) and nephroscope retrieval speeds on the efficacy of the vortex effect (VE) in mini-percutaneous nephrolithotomy (mini-PCNL). This study aimed to understand the poorly understood physical components of the VE. MATERIALS AND METHODS: A Pexiglas™ (KUS®) model was built based on the dimensions of a 15/16 F mini-PCNL set (Karl Storz). The flow rate was continuous via an automatic pump and calibrated to achieve hydrodynamic equivalence to the real equipment. One experiment consisted of manually retrieving all 30 stone phantoms (3 mm diameter) utilizing only the VE. Cumulative time to retrieve all stones was measured. An accelerometer recorded instant speeds of the nephroscope every 0.08 seconds (s), and 3 experiments were performed at each angle (0°, 45°, and 90°). A logistic regression model was built utilizing maximum speeds and access angles to predict the effectiveness of the VE. RESULTS: Mean cumulative time for complete stone retrieval was 28.1 seconds at 0° vs 116.5 seconds at 45° vs 101.4 seconds at 90° (P < .01). We noted significantly higher speeds at 0° compared to 45° and 90° (P < .01); however, differences in average and maximum speed between 45° and 90° were not statistically significant (P = .21 and P = .25, respectively). The regression model demonstrated a negative association between increasing maximum speed and VE's effectiveness (OR 0.547, CI 95% 0.350-0.855, P < .01). When controlling for maximum speed, the 0° angle had significantly higher chances of achieving at least a partially effective VE. CONCLUSION: Increasing the renal access angle or nephroscope extraction speed negatively impacts the effectiveness of the VE. This significantly increased procedure time in the laboratory model, suggesting that the VE is less effective at higher sheath angles.

The Vortex Effect in Minimally Invasive Percutaneous Nephrolithotomy.

OBJECTIVE: To describe the physical principles of the vortex effect to better understand its applicability in minimally invasive percutaneous nephrolithotomy (MIP) procedures. METHODS: Two acrylic phantom models were built based on the cross-sectional area (CSA) ratio of a MIP nephroscope and access sheaths (15/16F and 21/22F MIP-M, Karl Storz). The nephroscope phantom was 10 mm in diameter. The access sheaths had diameters of 14 mm (CSA ratio: 0.69) and 20 mm (CSA ratio: 0.30). The models were adapted to generate hydrolysis, and hydrogen bubbles enhanced flow visualization on a green laser background. After calibration, the experimental flow rate was set to 12.0 mL/s. Three 30-second trials assessing the flow were performed with each model. Computational fluid dynamic simulations were completed to determine the speed and pressure profiles. RESULTS: In both models, as the incoming fluid from the nephroscope phantom attempted to move toward the collecting system, a stagnation point was demonstrated. No fluid entered the collecting system phantom. Utilizing the 14 mm sheath, we observed a random generation of several vortices and a pressure gradient (PG) of 114.4 N/m2 between the nephroscope's tip and stagnation point. In contrast, examining the 20 mm sheath revealed a significantly smaller PG (19.4 N/m2) and no noticeable vortices were noted. CONCLUSION: The speed of the fluid and equipment geometry regulate the PG and the vortices field, which are responsible for the production of the vortex effect. Considering the same flow rate, a higher ratio between the CSA of the nephroscope and access sheath results in improved efficacy of the vortex effect.

On the rocks: can urologists identify stone composition based on endoscopic images alone? A worldwide survey of urologists.

PURPOSE: As part of the management of nephrolithiasis, determination of chemical composition of stones is important. Our objective in this study is to assess urologists' accuracy in making visual, intraoperative determinations of stone composition. MATERIALS AND METHODS: We conducted a REDCap survey asking urologists to predict stone composition based on intraoperative images of 10 different pure-composition kidney stones of 7 different types: calcium oxalate monohydrate (COM), calcium oxalate dihydrate (COD), calcium phosphate (CP) apatite, CP brushite, uric acid (UA), struvite (ST) and cystine (CY). To evaluate experience, we examined specific endourologic training, years of experience, and number of ureteroscopy (URS) cases/week. A self-assessment of ability to identify stone composition was also required. RESULTS: With a response rate of 26% (366 completed surveys out of 1,370 deliveries), the overall accuracy of our cohort was 44%. COM, ST, and COD obtained the most successful identification rates (65.9%, 55.7%, and 52.0%, respectively). The most frequent misidentified stones were CP apatite (10.7%) and CY (14.2%). Predictors of increased overall accuracy included self-perceived ability to determine composition and number of ureteroscopies per week, while years of experience did not show a positive correlation. CONCLUSIONS: Although endoscopic stone recognition can be an important tool for surgeons, it is not reliable enough to be utilized as a single method for stone identification, suggesting that urologists need to refine their ability to successfully recognize specific stone compositions intraoperatively.

Breakage Costs in Flexible Ureteroscopy: Digital vs. Fiberoptic Modalities.

OBJECTIVE: To compare the maintenance costs of digital flexible ureteroscopes (DFU) versus fiberoptic flexible ureteroscopes (FFU) to understand the long-term financial impact associated with breakage in a flexible ureteroscopy (f-URS) program. METHODS: Data for breakage of FFU and DFU at an academic institution from 2019 to 2021 were obtained from our vendor (Karl Storz) and analyzed by month. Correlation test was used to evaluate significant differences in number of procedures, number of breakage events, breakage rates, and repair cost per month. Cumulative analyses were utilized to examine the number of procedures before failure (time to failure - TTF) and repair costs per procedure (RCpP). RESULTS: We performed a total of 2,154 f-URS, including 1,355 with FFU and 799 with DFU (P<.001). Although we found a higher number of breakage events in FFU (n=124) than DFU (n=73) (P<.001), the overall breakage rate was similar, 9.9% vs. 8.8%, respectively (P=0.86). On cumulative analysis, both modalities reached the same TTF plateau (11 cases) after 18 months. After 400 cases, the RCpP for DFU was 1.25 times higher than for FFU (P=0.04). CONCLUSION: Overall, we found no difference in overall scope breakage rates between DFU and FFU. Although there was no difference in TTF over time, at the beginning DFU displayed considerable higher durability, leading to lower RCpP. Furthermore, DFU's endurance leveled off to FFU over time, resulting in higher RCpP after 400 cases. This finding may be explained by the presence of renewed scopes after repair.

Image Distortion During Flexible Ureteroscopy: A Laboratory Model Comparing Super Pulsed Thulium Fiber Laser vs High-Power Ho:YAG Laser.

Purpose: Digital ureteroscopes employ "chip-on-the-tip" technology that allows for significant improvement in image resolution. However, image distortion often occurs during laser lithotripsy owing to acoustic wave production. We sought to compare image distortion using different laser power settings and distances from the laser fiber tip to the scope for the Super Pulsed Thulium Fiber (SPTF) laser and high-power Holmium:YAG (Ho:YAG) laser. Materials and Methods: Ureteroscopy was simulated using a silicon kidney-ureter-bladder model fitted with a 12F/14F access sheath and the Lithovue™ (Boston Scientific), disposable digital flexible ureteroscope. At defined laser parameters (10, 20, 30 and 40 W, short pulse), a 200-µm laser fiber was slowly retracted toward the tip of the ureteroscope during laser activation. Image distortion was identified, and distance from the laser tip to the scope tip was determined. Data from the two lasers were compared utilizing t-tests. Results: After controlling for frequency, power, and laser mode, utilizing 1.0 J of energy was significantly associated with less feedback than 0.5 J (-0.091 mm, p ≤ 0.05). Increased power was associated with larger feedback distance (0.016 mm, p ≤ 0.05); however, increase in frequency did not have a significant effect (-0.001 mm, p = 0.39). The SPFT laser had significantly less feedback when compared with all Holmium laser modes. Conclusions: Increased total power results in image distortion occurring at greater distances from the tip of the ureteroscope during laser activation. Image distortion occurs further from the ureteroscope with Ho:YAG laser than with SPTF fibers at the same laser settings. In clinical practice, the tip of the laser fiber should be kept further away from the tip of the scope during ureteroscopy as the power increases as well as when utilizing the Ho:YAG system compared with the SPTF laser platform. The SPTF laser may have a better safety profile in terms of potential scope damage.