Erbium: YAG versus holmium: YAG lithotripsy

Purpose: We test the hypothesis that erbium:YAG (Er:YAG) lithotripsy is more efficient than holmium:YAG (Ho:YAG) lithotripsy. Materials and Methods: Human calculi composed of greater than 97% calcium oxalate monohydrate and cystine were studied. Calculi were irradiated in water using Er:YAG or Ho:YAG lasers. Er:YAG lithotripsy was done with a 425 μm. sapphire optical fiber at a pulse energy of 50 mJ. at 10 Hz. Ho:YAG lithotripsy was performed with a 365 μm. low hydroxy optical fiber at a pulse energy of 500 mJ. at 10 Hz. or a 425 μm. sapphire optical fiber at a pulse energy of 50 mJ. at 10 Hz. Fragmentation was defined as the initial stone mass minus the final dominant fragment mass and normalized for incident laser fluence (energy per unit area of fiber tip). Results: Mean fragmentation plus or minus standard deviation for calcium oxalate monohydrate was 38 ± 27 mg. for Er:YAG and 22 ± 6 for Ho:YAG (low hydroxy silica fiber) versus 5 ± 1 for Ho:YAG (sapphire fiber, p = 0.001). When fragmentation was normalized for incident laser fluence given different optical fiber sizes, mean fragmentation efficiency was 53.6 ± 38.7 g-μm.²/J. for Er:YAG lithotripsy compared with 22.6 ± 6.4 for Ho:YAG (low hydroxy silica fiber) lithotripsy (p = 0.04). Mean cystine fragmentation was 15 ± 3 mg. for Er:YAG versus 9 ± 1 for Ho:YAG (sapphire fiber, p = 0.0005). Conclusions: Er:YAG lithotripsy is more efficient than Ho:YAG lithotripsy.