Acute kidney injury (AKI) is a common and serious complication in the ICU. Current diagnostic indicators (such as creatinine and urine output) exhibit significant lag, and specific hemodynamic predictive markers are lacking. The venous return pressure gradient (Pmsf-CVP), based on Guyton's theory, reflects the driving pressure for venous return; however, its value in the early warning of AKI remains unclear. This study aims to investigate the predictive value of the venous return pressure gradient for the onset and progression of AKI in ICU patients, and to clarify its effectiveness as an AKI risk warning indicator.

Patients admitted to the ICU within 48 hours with risk factors for AKI (including sepsis, shock, major surgery, underlying diseases, etc.) who have radial artery catheterization and can undergo hemodynamic monitoring will be enrolled. Those undergoing maintenance dialysis/CRRT, ECMO support, or with missing core data precluding calculation of Pmsf-CVP or AKI assessment will be excluded.

The venous return pressure gradient (Pmsf-CVP, mmHg) will be measured within 48 hours of ICU admission using the transient stop-flow arm arterial-venous equilibrium pressure method. The primary outcome is to evaluate the association between the venous return pressure gradient level and AKI occurrence. Secondary outcomes include correlation analyses between the venous return pressure gradient level and serum creatinine and urine output within 48 hours of ICU admission, among others.