Holmium:YAG Laser Pulse Type Affects Irrigation Temperatures in a Benchtop Ureteral Model.J Endourol 2019JE
MOSES™ technology is a Holmium:YAG laser pulse mode shown to minimize stone retropulsion. This may facilitate lithotripsy at higher power settings. However, power and heat production are proportional, and temperatures capable of tissue injury may occur during ureteroscopic lithotripsy. While prior in vitro studies demonstrate the importance of irrigation and activation time on heat production, the impact of pulse type has not been evaluated.
A flexible ureteroscope with a 365μm laser fiber was placed in an 11/13Fr access sheath inserted into a 250cmL saline bag to simulate a ureter, renal pelvis, and antegrade irrigant flow. A thermocouple was placed adjacent to the laser tip, and the laser fired for 30 sec at 0.6J/6Hz, 0.8J/8Hz, 1J/10Hz, 1J/20Hz, and 0.2J/70Hz at irrigation pressure of 100mmHg. 4 runs were tested per setting using short pulse(SP), long pulse(LP), MOSES-contact(MC) and MOSES-distance(MD) modes. The mean temperature changes(dT) were compared and thermal dose calculated in Cumulative Equivalent Minutes at 43°C(CEM43) using an adjusted baseline of 37°C. CEM43 ≥120 minutes was considered the tissue injury threshold.
At 0.8J/8Hz, LP produced the greatest dT, significantly higher than MC(p=0.041). CEM43 did not exceed the injury threshold. At 1J/10Hz, dT was significantly higher for LP versus MC and MD(p=0.024, 0.045). Thermal dose remained below the injury threshold. No differences in dT were seen between pulse types at 0.6J/6Hz, 0.2J/70Hz, or 1J/20Hz. At 1J/20Hz, thermal dose exceeded the injury threshold for all pulse types within 3 seconds.
Laser pulse type and length appears to impact heat production in our ureteral model. Long pulse produced significantly greater temperatures at 0.8J/8Hz and 1J/10Hz relative to MOSES™ settings. Fortunately, thermal dose remained safe at these settings. Both long pulse and MOSES™ technology are known to reduce stone retropulsion; the latter may confer this advantage with reduced heat.