Laser-mediated tripsy: a controlled disintegration of urinary stones

Introduction. The development of infectious/inflammatory processes in kidneys in among the most common complications of nephrolithotripsy due to fragmentation of urinary stones into small particles and dissemination of bacteria from infected stone-derived biofilms into the kidney cavity system. The search for new methods of stone fragmentation implying controlled large comminuted fragmentation will allow not only to minimize possible contamination of the urinary system but also to prevent the loss of small particles of the disintegrated stone, which account for residual lithiasis. Aim. The search for a mode of laser lithotripsy, which will ensure effective fragmentation of kidney concrements excluding their uncontrolled disintegration into small particles. Materials and methods. In a series of experiments we used the Ho:YAG laser with thulium fiber laser pumping. The pulses generated by the Ho:YAG laser had the wavelength of 2097 nm whose duration was 20-40 ns and frequency varied from 5 to 40 kHz; the mean value of power was 35 W (pulse energy varied from 0.5 to 3.0 mJ). We also used the Tm:Lu2O3 ceramic laser with an erbium-pumped laser with the Raman shift at 1670 nm. This ceramic laser was emitting at 1967 nm in a pulsed-periodic regime (the duration and frequency of pulses were 30-40 ns and 14-25 kHz, respectively); mean power values varied from 100 mW to 10 W. Both lasers were created in the Institute of Applied Physics, Russian Academy of Sciences (Nizhny Novgorod). The duration of transverse stone perforation (before the passage of a pulse through the stone) was recorded; the newly formed tunnel was analyzed both visually and using light microscopy. The effect of laser fragmentation on 25 stones ex vivo was studied. Results. In a series of experiments, we have determined that the optimal mode of laser generation at 2097 nm for controlled lithotripsy implies the frequency of pulses from 200 to 1000 Hz and their energy of 45-55 mJ. This means that the mode of laser generation with a relatively low pulse energy (tens of mJ) but high frequency of pulses (hundreds of Hz - tens of kHz) ensures the destruction of concrements into fragments which can be accessed through Amplatz sheath. The duration of transverse perforation was from 2 to 300 seconds and depended on the density, length and chemical composition of the stone. Conclusion. Controlled destruction not followed by dissemination of the stone-derived particles through the kidney cavity could be a solution for the prevention of infectious/inflammatory processes after nephrolithotripsy, which could be achieved by adjusting the mode of laser-mediated contact lithotripsy.