Optimization of the parameters of a superpulse thulium fiber laser with wavelength 1.94 μm for minipercutaneous lithotripsy

At present, minipercutaneous nephrolithotripsy is a highly effective and safe method for fragmentation of stones with sizes up to 3 cm. The use for lithotripsy of a holmium: yttrium aluminum garnet laser with wavelength 2.1 μm (Ho:YAG) is a common practice today. Of late, however, more attention is paid to a new superpulse thulium fiber laser with wavelength 1.94 μm and maximum output power 40 W. The use of a thulium laser with pulse energy 0.025–6 J and a high repetition rate (to 1600 Hz) permits to obtain (compared with a holmium laser) better results of stone dusting. Objective. Selection of the optimal modes of stone fragmentation in minipercutaneous nephrolithotripsy with the use of a superpulse thulium fiber laser with wavelength 1.94 μm and maximum output power 40 W in patients with nephrolithiasis. Patients and methods. The study included patients (n = 171), who underwent minipercutaneous nephrolithotripsy using a superpulse thulium fiber laser during the period from February 2018 to July 2019. The following parameters of laser radiation were used: pulse energy 0.1-6 J, power 6-40 W, pulse rate 30-300 Hz. The impact of modes on endoscopic visualization and retropulsion was assessed intraoperatively. Results. Statistical analysis of the specificities of the most often used modes was conducted: No 1 – «0.15 J, 200 Hz, 30 W», No 2 – «0.5 J, 30 Hz, 15 W», No 3 – «0.8 J, 31.25 Hz, 25 W», No 4 – «0.8 J, 37.5 Hz, 30 W», No 5 – «1.5 J, 15 Hz, 30 W», No 6 – «1.5 J, 26.6 Hz, 40 W», No 7 – «2 J, 15 Hz, 30 W», No 8 – «2 J, 20 Hz, 40 W», No 9 – «4 J, 10 Hz, 40 W»; their effects on retropulsion and on endoscopic visualization were studies. The stone free rate was assessed on the first post-operative day according to the findings of low-dose CT. Conclusion. Study of the modes of thulium fiber lithotripsy, assessment of retropulsion and endoscopic visualization depending on the choice of emitted radiation parameters of a thulium fiber laser make it possible to improve the outcomes of operative treatment in patients with nephrolithiasis. Key words: minipercutaneous, nephrolithotripsy, nephrolithiasis, MPNL, thulium fiber lithotripsy, retropulsion, visibility, superpulse thulium fiber laser, wavelength 1.94 μm, stone free rate