The use of laser doppler flowmetry to assess the microcirculation of the kidney before and after percutaneous nephrolithotomy

Aim. To evaluate intraoperative changes in renal microcirculation during percutaneous nephrolithotomy (PCNL), as well as its dynamics in the early postoperative period.

Materials and methods. A total of 240 patients treated in the Urology Clinic of the Saratov State Medical University in 2021-2022 were included in the study. All patients underwent PCNL. In the first group (n=105) the standard PCNL through 30 Ch access was done. In the second group (n=135), the procedure was performed through an access of 16 Ch. Intraoperatively, intrapelvic pressure was evaluated according to the author’s method, which consists in direct measurement in the collecting system during the procedure, allowing for a faster and more accurate assessment. Prior to surgery, Doppler mapping of the renal blood flow was performed, and indirect registration of the microcirculation index (MCI) was done directly on the operating table using laser Doppler flowmetry (LDF). The diagnostic study was performed at the point of intersection of the 12th rib and the psoas muscle, both on the ipsilateral and contralateral side. In addition, during the procedure, a registration of MI of the mucosa of the calyceal fornix accessible in the direct vision through the access tract for 4 minutes was carried out twice.

Results. The index of microcirculation (IM) in the fornix of the upper calyx before the fragmentation of the stone in the 1st group of patients was 26.67±4.7 pf.u. compared to 25.4±5.9 pf.u. in the second group. At the same time, the value recorded on the skin was 13.08±1.2 pf.u. in the first group compared to 13.1±0.77 pf.u. in the second group (p>0.05). During the initial registration, the PM immediately after stone fragmentation was 19.5 ± 1.2 pf.u, while on the overlying skin it was 11.2 ± 0.9 pf.u. In the contralateral kidney area, IM was 10.2±0.9 pf.u. In the case of an intraoperative increase in intrapelvic pressure, IM was 22.3±1.6 pf.u. compared to 12.1±0.7 pf.u on the skin. The dynamics of IM on the skin tended to further decrease and returned to normal values of 10.3 ± 0.7 pf.u on the 3rd day. When intraoperative intrapelvic pressure exceeded the normal value, IM by the 5th day was 10.1±0.4 pf.u. When determining the correlation of IM with RI of the ipsilateral kidney, a direct moderate correlation was revealed (r=+0.516).

Conclusion. The measurement of microcirculation in the intra- and postoperative period allows to assess changes in the intrarenal microcirculation both directly and indirectly. This method can be used as an additional tool for assessing obstructive changes and the activity of pyelonephritis. A significant correlation between IM and RI indicates that functional changes in the renal and skin microcirculation tend to develop simultaneously.