Volume Removal Intolerance During Net Ultrafiltration in Acute Kidney Injury Patients

Acute kidney injury (AKI) is common in critically ill patients and is frequently associated with fluid overload, which can worsen clinical outcomes. Continuous renal replacement therapy (CRRT) allows fluid removal through net ultrafiltration (UFNET), but some patients develop hemodynamic instability or signs of poor tissue perfusion during this process. The purpose of this prospective observational study is to evaluate tolerance to net ultrafiltration in critically ill patients with AKI receiving CRRT. The study will assess clinical, hemodynamic, ultrasound, perfusion, and biochemical parameters before and during fluid removal to identify factors associated with ultrafiltration intolerance. The investigators hypothesize that alterations in hemodynamic, perfusion, and congestion-related parameters can identify patients at increased risk of ultrafiltration intolerance before the development of overt hypotension. The results may help improve individualized fluid removal strategies and optimize the safety of CRRT in critically ill patients.

Inclusion Criteria: * Age ≥18 years * Admission to an Intensive Care Unit * Acute kidney injury according to KDIGO criteria * Prescription of continuous renal replacement therapy (CRRT) with net ultrafiltration * Clinical stability considered sufficient to initiate net ultrafiltration according to the treating clinical team Exclusion Criteria: * Chronic kidney replacement therapy prior to ICU admission * Pregnancy * Limitation of therapeutic effort or goals-of-care decisions at admission or during the observation period * Inability to perform hemodynamic or perfusion assessment * Extracorporeal membrane oxygenation (ECMO) * Refusal to participate in the study