Critically ill patients with acute kidney injury (AKI) are at high risk of bleeding on account of coagulopathy, platelet dysfunction, frequent liver dysfunction and invasive procedures.In patients at high risk of bleeding, anticoagulation restricted to the circuit (regional anticoagulation) has been advocated as the method of choice.However, citrate anticoagulation may have many metabolic consequences, such as metabolic alkalosis due to citrate metabolism into bicarbonate, and in patients with liver disease, metabolic acidosis and hypocalcemia may occur.Implementation of citrate-based regional anticoagulation with frequent monitoring of acid-base and electolytes is also more challenging for the nurses and does not eliminate the need of a low-dose systemic anticoagulation for thromboses prophylaxis in most of the patients. Citrate-based regional anticoagulation is therefore mainly advocated only for patients at high-risk of bleeding.

The investigators plan to implement an open-label randomized control trial assessing the effectiveness of citrate-based regional anticoagulation in critically ill patients with AKI and with a special emphasis on the safety profile of this treatment in patients with severe liver failure.

monocentric prospective open-label randomized controlled trial at the ICU of the University Hospitals of Geneva (Switzerland).

ICU patients eligible if they 18 yr old and had an AKI requiring CRRT Exclusion criteria Patients excluded if they had active hemorrhagic disorders or severe thrombocytopenia (< 50x109/L), a history of heparin-induced thrombocytopenia, severe liver failure defined as a factor V <20% or were on the waiting list for liver transplantation.

Treatment assignment Subjects enrolled into the trial randomly allocated to either heparin or citrate anticoagulation

Inclusion Criteria:

• Patients with acute kidney injury requiring renal replacement therapy (RIFLE criteria)
• Patients (males or females) > 18 yrs old
• Consent form signed (or in emergency investigator's statement form)

Exclusion Criteria:

• Patients with active bleeding disorders
• Patients with past history of heparin-induced thrombocytopenia (HIT)
• Patients with very severe liver disease ( patients awaiting liver transplant or factor V < 20% or MELD score > 25)
• Pregnancy (negative pregnancy test required in child-bearing age women prior to inclusion)
• Enrollment in another concurrent therapeutic trial