Residual renal function (RRF) plays a critical role in quality of life and survival in hemodialysis (HD) patients but characteristically declines after the initiation of HD. Owing to incomplete understanding of the pathophysiology underlying RRF decline, protective strategies remain limited. The aim of this study was to characterize the changes in renal perfusion in incident HD patients with preserved RRF during dialysis sessions and to provide new strategies for RRF preservation.

Inclusion Criteria:

• (1) adult patients with end-stage renal disease (ESRD) within 3 months of commencing HD; (2) preserved RRF defined as urinary output >500 mL/24 h or eGFR ≥3 mL/min/1.73 m²

Exclusion Criteria:

• (1) known allergy to sulfur hexafluoride microbubbles (SonoVue®) microbubbles; (2) vascular access dysfunction; (3) combined peritoneal dialysis; (4)severe cardiopulmonary disease; (5) active infection or malignancy; (6) communicable diseases; (7) pregnancy or breastfeeding; (8) participation in other clinical trials.

A total of thirty patients from the First Medical Center of Chinese PLA General Hospital were consecutively enrolled in the study (as detailed in the Study Design section) after providing written informed consent.