Purpose: Retrograde intrarenal surgery is the gold-standard treatment for most kidney stones. During ureteroscopy, ureteral access sheath insertion at forces greater than 8.0 Newtons (N) risks high-grade ureteral injury. To monitor force, our institution utilizes a unique, Bluetooth-equipped device (i.e., the University of California—Irvine Force Sensor). Given the unique nature of the force sensor, we sought to develop an inexpensive and accessible force sensor based on Boyle’s law and the specific amount of force required to compress an occluded 1.0 mL syringe. Materials and Methods: We evaluated three brands of 1.0 mL syringes. After setting the plunger at 1.0 mL, the syringe was occluded, and the syringe plunger was compressed. The syringe volume was recorded when the applied force on the plunger reached 4.0 N, 6.0 N, and 8.0 N. Multiple trials were performed to assess reliability and reproducibility. A method for applying this clinically was also developed. Results: The precise force thresholds identified for a 1.0 mL Luer-Lok™ Syringe (Becton Dickinson, Franklin Lakes, NJ) were 0.30 mL for 4.00 N, 0.20 mL for 6.00 N, and 0.15 mL for 8.00 N. The 1.0 mL Tuberculin Syringe and 1.0 mL Luer Slip Syringe were less precise, but compression from 1.0 to 0.40 mL, 0.25 mL, and 0.20 mL corresponded to force sensor readings that did not exceed 4.00 N, 6.00 N, and 8.00 N, respectively. Conclusions: Based on volume changes, 4.00 N, 6.00 N, and 8.00 N of force can be reliably and reproducibly achieved using an occluded 1.0 mL syringe.

Background/Objectives: Emerging laser systems in endourology require further head-to-head trials to evaluate their ablation efficiency, or the amount of stone treated per energy spent. To answer this question, we built an in vitro model to compare stone ablation efficiency between the holmium:YAG with pulse modulation (Moses), pulsed thulium:YAG (pTm:YAG), and Thulium Fiber Laser (TFL) using dusting and fragmentation settings on uric acid (UA) and calcium oxalate monohydrate (COM) stones. Methods: We built an in vitro system with 24 UA and 18 COM stones fixed onto Petri dishes and submerged into warm saline. We used 200-micron laser fibers with settings of 0.3 J × 30 Hz for dusting and 1 J × 10 Hz for fragmenting. Each laser was fired while contacting the stone for 1 s per trial. Ablated stone volume was measured using Optical Coherence Tomography (OCT). A one-way Analysis of Variance (ANOVA) was conducted to determine differences in mean efficiency of laser fibers at different settings, with significance assessed at p < 0.05. Results: In total, 81 craters created by laser ablation were detected via OCT. When fragmenting UA stones, pTm:YAG was the most efficient, averaging 116.8 mm³/kJ, compared to 110.8 for TFL and 51.4 for Moses (p = 0.0003). There were no differences on the dusting setting for UA. TFL was the most efficient in fragmenting COM stones with 69.2 mm³/kJ, compared to 49.5 for pTm:YAG and 32.7 for Moses (p = 0.0024). Finally, pTm:YAG was the most efficient for dusting COM stones, with 30.5 mm³/kJ, compared to 23.8 for TFL and 14.5 (p = 0.0175). Conclusions: Pulsed Tm:YAG exhibited the most efficient fragmentation of UA stones and dusting of COM stones, while TFL was the most efficient for fragmenting COM stones.