The plenary panel, Optimal Laser Technology for Stone Management, was broadcast online Saturday, September 10, 2021 during the virtual AUA annual meeting. I had the privilege to moderate the session, which included presentations on low power holmium (Ho):YAG lithotripsy, variable pulse Ho:YAG lithotripsy, pulse modulated Ho:YAG lithotripsy and thulium fiber laser (TFL) lithotripsy.

Dr. Margaret Pearle from UT Southwestern presented the case for low power Ho:YAG lithotripsy. She characterized these low power Ho:YAG lasers as under 35 W power, with pulse energies from 0.4 to 5 J, with pulse durations about 350 μsec. She noted equivalent stone-free outcomes using low power versus high power (120 W) Ho:YAG lasers, with a slightly longer lithotripsy time for the low power cohort in 1 study.¹ Another study comparing in vitro calyceal and ureteral models for lithotripsy showed low power Ho:YAG laser settings can achieve the same fragmentation as high power machines.² She pointed out these lasers provide ability to dust and fragment, but with much reduced range of settings compared to newer lasers. She noted the cost of low power Ho:YAG machines as less than half of 120 W units and less than a third of pulse modulated units, and characterized the low power Ho:YAG units as a “workhorse” that gets the job done!

Dr. Mordechai Duvdevani from the Hebrew University, Israel presented the case for variable pulse Ho:YAG lasers. He reviewed the differences of pulse duration, with some Ho:YAG lasers describing a short or standard pulse generally under 140 μsec and then a long pulse generally 350–700 μsec. He noted some lasers also give a medium pulse. The longer pulse yields less retropulsion and less fiber burn-back compared to the shorter pulse duration.^3,4 The shorter pulse often is used for fragmentation settings, with higher peak power and more photons above criterion threshold for stone ablation, whereas with long pulse, more photons go toward water absorption and increased temperature. He cited a paper showing the long pulse had the highest temperature rise, controlling for all other factors, compared to shorter pulse durations or to pulse modulation settings.⁵

Dr. Oriol Angerri Feu from Universitat Autònoma de Barcelona, Spain presented the case for pulse modulated Ho:YAG lithotripsy, where a first pulse is synchronized with a second pulse that can ride the initial vapor bubble through the “Moses” channel. He showed different pulse modulation modes that provide for reduced retropulsion in contact lithotripsy, and enhanced fragmentation working with a step-off distance from the stone.⁶ He mentioned several branded pulse modulation Ho:YAG lasers and showed a graphic of each of these vapor bubbles simultaneously to demonstrate the differences. He added that more research is required to better define which setting works optimally. Echoing Dr. Duvdevani, he noted longer pulse durations (compared to shorter pulse durations) cause more heating of the aqueous environment, risking potential thermal injury to the ureter in long pulse durations even with just a few seconds of use.

Dr. Oliver Traxer from Sorbonne University in Paris presented the case for TFL. He noted preclinical data that support higher water absorption, smaller fragments and less retropulsion than Ho:YAG.⁷ He referenced data showing TFL efficacy and stated that more confirmatory research is needed.⁸ He, too, cautioned against using long pulse durations or high power TFL settings that might risk thermal injury to the ureter.

In the remaining live discussion, I posed several questions to the presenters, including, “What is your preferred setting and fiber for your designated machine?” For a 7 mm ureteral stone, their preferred settings were low power Ho:YAG laser (200–272 μm fiber, 0.5–0.8 J at 8–12 Hz), variable pulse Ho:YAG laser (200 μm fiber for flexible ureteroscopy, 365 μm fiber for semirigid ureteroscopy, 0.5–0.6 J pulse energy, 20 Hz, short pulse), pulse modulated Ho:YAG laser 200–230 μm fiber, 0.2 J at 40 Hz, contact or distance settings) and TFL (150 μm fiber, 0.3–0.5 J, 10–20 Hz, short pulse). For a 12 mm lower pole renal stone, their preferred settings were low power Ho:YAG (200–272 μm fiber, 0.8 J pulse energy for fragmentation setting, 8–12 Hz, short pulse if posible and displace the stone if the angle is difficult), variable pulse Ho:YAG (200 μm fiber, short pulse 0.2 J with maximal frequency but maximum power of 24 W to avoid thermal injury) and TFL (150 μm fiber, 0.3–0.5 J pulse energy, short pulse to achieve high peak power, frequency 20–50 Hz, maximum power 24 W to avoid thermal injury).

When the panel members were asked, “If you had to pay out of pocket with your own money for any of these machines, what would you purchase?” the answers ranged from reliable, workhorse low power Ho:YAG to higher tech pulse modulated Ho:YAG and TFL!