Holmium:YAG percutaneous nephrolithotomy: The laser incident angle matters

Purpose: Laser physics dictate that maximal radiant exposure occurs when the laser strikes the target at a normal incidence. Since the renal collecting system often limits nephroscope movements during percutaneous nephrolithotomy, the laser-calculus incidence angle may vary. We have observed during holmium:YAG percutaneous nephrolithotomy that the side firing fiber more easily approaches a normal incidence compared to the end firing fiber. We test the hypothesis that holmium:YAG percutaneous nephrolithotomy is faster with a side firing fiber compared to an end firing fiber. Materials and Methods: Consecutive holmium:YAG percutaneous nephrolithotomy cases were studied retrospectively. The calculus size and composition, surgical time, fragmentation speed (size/time) and stone-free rates were compared between 11 patients treated with end and 8 treated with side firing fibers. Results: When the end and side firing groups were compared, calculus sizes (mean plus or minus standard deviation) were 22 ± 13 versus 48 ± 17 mm. (p = 0.004), calcium oxalate monohydrate incidence was 55 versus 75% (p = 0.3), surgical times were 168 ± 87 versus 124 ± 51 minutes, computed fragmentation speeds were 0.15 ± 0.09 versus 0.43 ± 0.15 mm. per minute (p = 0.0009) and stone- free rates were 73 versus 88% (p = 0.4), respectively. Conclusions: The side firing fiber is faster than the end firing fiber for holmium:YAG percutaneous nephrolithotomy. These results are consistent with principles of laser physics.