Holmium:YAG lithotripsy efficiency varies with energy density

Purpose: We test the hypothesis that holmium:YAG lithotripsy efficiency varies with optical fiber size and energy settings (energy density). Materials and Methods: The 272, 365, 550 and 940 μm. optical fibers delivered 1 kJ. total holmium:YAG energy to calcium oxalate monohydrate calculi at energy output/pulse of 0.2 to 1.5 J. Stone mass loss was measured for each fiber energy setting. Stone crater width was characterized for single energy pulses. Fiber energy outputs were compared before and after lithotripsy. Results: Stone mass loss correlated inversely with optical fiber diameter (p <0.05). Stone loss correlated with energy/pulse for the 365,550 and 940 μm. fibers (p <0.001). The 272 and 365 μm. fibers yielded equivalent stone loss at 0.2 and 0.5 J. per pulse. At energies of 1.0 J. per pulse or greater the 272 μm. optical fiber was prone to damage, and yielded reduced energy output and stone loss compared to the 365 μm. fiber (p <0.01). Stone crater width for single pulse energies correlated with energy settings for all fibers (p <0.001). Conclusions: Lithotripsy efficiency with the holmium:YAG laser depends on pulse energy output and diameter of the optical delivery fiber, implying that lithotripsy efficiency correlates with energy density. The 365 μm. fiber is indicated for most lithotripsy applications. The 272 μm. fiber is susceptible to damage and inefficient energy transmission at energies of 1.0 J. per pulse or greater. The 272 μm. fiber is indicated at energies of less than 1.0 J. per pulse for small caliber ureteroscopes or when maximal flexible ureteroscope deflection is required.