In the present prospective multicenter RCT we will evaluate the effects on efficacy, acid-base status and serum phosphate levels of a new RCA protocol for Continuous Venovenous Hemodiafiltration (CVVHDF) using an 18 mmol/l citrate solution in combination with a calcium-free phosphate-containing solution, acting as dialysate and replacement fluid. The new protocol will be introduced with the following targets: a) to refine buffers balance of a previously adopted RCA protocol for Continuous Venovenous Hemofiltration (CVVH), based on a 18 mmol/l citrate solution (Regiocit) combined with calcium and phosphate-free dialysate fluid (PrismOcal B22) and a conventional phosphate-containing replacement fluid (Phoxilium) to prevent CRRT-related phosphate depletion

Inclusion Criteria:

1. Acute renal failure requiring CRRT
2. Suitability for regional anticoagulation of the CRRT circuit
3. Clinical equipoise regarding the method of circuit anticoagulation
4. Subject is affiliated with a social security system (if required by individual country regulations).
5. Subject meets national regulatory criteria for clinical trial participation.
6. Subject or subject's Legally Authorized Representative (LAR) has signed the study Informed Consent form

Exclusion Criteria:

1. Age less than 18 years
2. Expected stay in ICU less than 24 hours
3. Pregnant or breastfeeding
4. Suspected ischemic hepatitis or liver failure
5. Chronic kidney disease requiring dialysis prior to ICU admission
6. As applicable by French law, subject who is a protected individual such as an incompetent adult or incarcerated person
7. Metformin and acethaminophen intoxication