HOLMIUM-YAG LITHOTRIPSY EFFICIENCY VARIES WITH ENERGY DENSITY

Purpose: We test the hypothesis that holmium:YAG lithotripsy efficienc y varies with optical fiber size and energy settings (energy density). Materials and Methods: The 272, 365, 550 and 940 mu m. optical fibers delivered 1 kJ. total holmium:YAG energy to calcium oxalate monohydra te 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 charac terized for single energy pulses. Fiber energy outputs were compared b efore and after lithotripsy. Results: Stone mass loss correlated inver sely with optical fiber diameter (p <0.05). Stone loss correlated with energy/pulse for the 365, 550 and 940 mu m. fibers (p <0.001). The 27 2 and 365 mu m. 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 mu m. o ptical fiber was prone to damage, and yielded reduced energy output an d stone loss compared to the 365 mu m. fiber (p <0.01). Stone crater w idth for single pulse energies correlated with energy settings for all fibers (p <0.001). Conclusions: Lithotripsy efficiency with the holmi um:YAG laser depends on pulse energy output and diameter of the optica l delivery fiber, implying that lithotripsy efficiency correlates with energy density. The 365 mu m fiber is indicated for most lithotripsy applications. The 272 mu m. fiber is susceptible to damage and ineffic ient energy transmission at energies of 1.0 J. per pulse or greater. T he 272 mu m. fiber is indicated at energies of less than 1.0 J. per pu lse for small caliber ureteroscopes or when maximal flexible ureterosc ope deflection is required.