MP18-18 THE EFFECTS OF STONE DUSTING SETTINGS ON URETERAL AND CALYCEAL STONES IN A BENCH TOP MODEL

Abstract

INTRODUCTION AND OBJECTIVES: Studies have shown higher stone fragmentation and retropulsion rates associated with higher pulse energy settings using the Ho:YAG laser. However, the optimal settings for laser lithotripsy in the kidney and ureter have not been defined. The purpose of this study was to compare conventional holmium laser settings with high frequency low energy (stone dusting) settings using in-vitro calyceal and ex-vivo porcine ureteral models. METHODS: Calyceal model: The model was constructed by mounting a metal sieve with 0.92mm pores onto a 15mm diameter hollow tube. Nine groups of 3 human calcium oxalate monohydrate (COM) stones of matched size and weight were placed on the sieve and fragmented using three different laser settings (0.6J/5Hz, 0.2J/15Hz, and 0.2J/50Hz). A 200mm fiber was used. All stones were fragmented until they passed through the larger sieve and the residual stone fragments were collected on a sieve with finer pores (0.25mm) directly below. The time to completion, energy used, and the residual fragment weights were recorded. Ureteral model: Fresh porcine ureters were collected and submerged in saline. Paired trials using two different settings (0.6J/5Hz and 0.2J/15Hz) were conducted in each ureter using human COM stones of matched size and weight. Ten minutes of laser lithotripsy using a flexible ureteroscope and a 200mm Holmium laser fiber was performed. The trials were stopped if the stone retropulsed to the opposite end of the ureter. The rate of retropulsion, time to completion, energy used and residual stone fragment weights were recorded. The Kruskal-Wallis and Mann-Whitney U tests were used as appropriate for statistical analysis with p<0.05 deemed significant. RESULTS: In the renal pelvic model, the 0.2J/15Hz dusting setting resulted in longer lithotripsy time (615.7s) compared to the 0.6J/ 5Hz (389.0s) or 0.2J/50Hz setting (395.3s; p = 0.006). Total energy required for complete stone fragmentation increased with increasing frequency settings (261 vs. 454 vs. 910 J for 0.6J/5Hz, 0.2J/15Hz and 0.2J/50Hz, respectively; p<0.001). Residual fragment weights and the stone vaporization weights were comparable (p=0.444, 0.697; respectively). In the ureteral model, retropulsion rate was much higher for the 0.6J/ 5Hz setting than the 0.2J/15Hz (43.7 vs 12.9 mm/min; p<0.001). CONCLUSIONS: Stone dusting settings were inferior in the renal pelvis as they required longer fragmentation time compared to conventional settings. In the ureter dusting settings were found to result in significantly less stone retropulsion.