High Frequency Non-contact Holmium Laser Lithotripsy: Impact of Pulse Energy and Time on Fragmentation
•Non-contact high-frequency holmium laser lithotripsy (pop-corn effect) is performed when the laser fiber is rapidly activated away from the stone surface, resulting in a whirlpool like phenomenon that causes stones to fragment.
•A prior study by Bagley et al demonstrated settings of 1.5 J and 40 Hz resulted in the best stone disintegration with fragments <2 mm.
•The aim of this study was to assess the optimal time needed to achieve disintegration into <1mm fragments (dusting effect), and the impact of these settings on fiber tip degradation and burnback.
•Stone phantoms were prepared using Begostone (15:3 powder to water ratio)
•Stones were disc shaped (5 mm x 2-3 mm each) and three stones were used for each experiment (weight 0.3g)
•A glass vial (inner diameter 14 mm / length 60 mm) was used to simulate a caliceal model.
•Flow was introduced using an open-ended 4 Fr ureteral catheter, connected to a saline bag placed at 150 mmHg pressure, to mimic flow from the working channel of a ureteroscope.
•The laser fiber was positioned 2 mm away from the highest stone and held in place using a fiber chuck attached to a 3-D positional gantry system (figure 1).
•Each experiment was done using 1.5 J X 40 Hz, for a duration of 2, 4, and 6 minutes.
•The study was performed utilizing a 60-W laser (VersaPulse PowerSuite, Lumenis, CA) and a 200 µm fiber (Flexiva 200, Boston Scientific, MA).
•Stone larger than 0.5 mm were retained and weighted to determine loss in mass.
•Fiber tip length was measured before and after each experiment using a digital caliber (Fisher Scientific, NH) to determine fiber burnback.
•At 1.5 J X 40 Hz setting, the mean percentage loss in stone mass was 41.3% (SD 10.6), 71.5% (SD 9.0), and 86.2% (SD 6.6) at 2, 4, and 6 minutes respectively (figure 2).
•Stone fragmentation results were significantly different when non-contact lithotripsy was performed for 4 vs 2 minutes (P < 0.05); however, fragmentation results between 4 and 6 minutes were not statistically significant (P = 0.08) (Figure 1).
•The mean loss in fiber length (burnback) was 2.1 (SD 0.7), 3.2 (SD 0.8), and 4 (SD 0.9) mm at 2, 4, and 6 minutes respectively.
•We found an increase in both stone disintegration and fiber burnback with increasing non-contact lithotripsy time.
•When using 1.5 J x 40 Hz, at least 4 minutes is needed to achieve >50% stone fragmentation at the sub-millimeter level.
•Clinical studies are needed to validate these in vitro findings.