Introduction. The least invasive technique of PCNL is micropercutaneous nephrolithotripsy (micro-PCNL). A possibility of kidney puncture under direct endoscopic control with the creation of a working channel sized of 8-4.85 F is a characteristic feature of this system.
Aim. To study the possibilities of micro-PCNL and to determine its role in the treatment of kidney stones.
Materials and methods. A total of 74 patients aged 49.8±16.3 years were included in the study. In majority cases an isolated kidney stone was diagnosed (86.4%). The most common stone localization was pelvis (51.5%), followed by lower pole (35.9%). Considering the technical aspects of microPCNL, all patients were divided into 2 groups depending on the stone burden. In 46 patients (62.1%), the stone size was < 1.5 cm, while in 28 patients (37.9%) stones were bigger than 1.5 cm. Prestenting was performed in 54.0% due to renal colic or obstructive pyelonephritis. For the purpose of passive flushing of stone fragments during the lithotripsy, in most patients with a stone size > 1.5 cm, as well as in some prestented patients a ureteral access sheath with a diameter of 10/12 F (56.7%) was placed under x-ray control. In most patients with stones less than 1.5 cm, a 4.85 Ch sheath was utilized. In patients with larger stones, working sheath of 8 Ch was put. For stone disintegration, 50 W and 100 W holmium lasers, as well as the Russian innovative thulium fiber laser were used.
Results. The average duration of surgery from the puncture was 30.6±11.6 minutes. The effectiveness was determined by use of a non-contrast computed tomography, performed one month after the surgery. An overall stone-free rate after one-session was 89.1%, and it was 93.4% and 82.4%, respectively, in patients with stones sized less and more than 1.5 cm. In 32.4% cases the stenting was placed due to the large number of small residual fragments and risk of obstruction. In one case, a conversion into a mini-PCNL was done. Two patients (2.7%) required stenting because of renal colic caused by the migration of stone fragments into the ureter. There was no bleeding. In 8.1% of cases, acute pyelonephritis was developed that was treated conservatively. In 9.4% of patients, ESWL was required due to residual stones diagnosed one month after the surgery.
Conclusion. Micro-PCNL is highly effective and safe method for treatment of kidney stones. Placing of ureteral access sheath of size 10/12 F contributes to the passive flushing of fragments during lithotripsy, which, together with the use of the 8 F working sheath, makes it possible to effectively perform micro-PCNL in patients with kidney stones larger than 1.5 cm.

Keywords: ureteral access sheath, thulium fiber laser, all-seeing needle, micropercutaneous nephrolithotomy, holmium laser