High-power laser lithotripsy – do we treat or harm? Histological evaluation of temperature effects in an in vivo study with thulium fiber laser

INTRODUCTION: The aim of this study was to evaluate the possible histopathological alterations that occur in the kidneys due to a continuous temperature increase above 43°C for one hour of lithotripsy using a newly introduced thulium fiber laser (TFL). MATERIAL AND METHODS: Two female pigs were used. After the insertion of a 9.5/11.5 ureteral access sheath, flexible ureteroscopy and laser lithotripsy for one hour were conducted. A TFL laser with a 200-μm fiber was used. The power setting used was 8 W (0.5 J × 16 Hz). A K-type thermocouple was inserted and fixed in the upper calyx of the right porcine kidney to record the temperature in the pelvicalyceal system during the laser activation. Second-look flexible nephroscopy followed by nephrectomy and pathohistological evaluation of the operated kidney was performed one week after the procedure in the first pig and 2 weeks after the surgery in the second pig. RESULTS: Flexible nephroscopy did not reveal significant differences between the 2 porcine kidneys. Nevertheless, the histopathological report demonstrated severe alterations in the kidney of the first pig. Mild changes were reported in the kidney of the second pig. A significant improvement in inflammation and haemorrhagic lesions was demonstrated when comparing the 2 kidneys. CONCLUSIONS: The difference demonstrated between the 2 kidneys based on the histopathological report shows that the healing process is capable of improving severe to mild alterations within a one-week time frame. Two weeks after the surgery, only minor changes were observed, suggesting that even temperature increases above the threshold can be tolerated regarding renal damage.