A prospective randomized study conducted in critically ill patients with acute kidney injury (AKI), treated with CVVH, with either low dose citrate (2.5 mmol/L blood flow in the filter) or high dose citrate (4.5 mmol/L blood flow in the filter) as anti-coagulant, targeting a postfilter ionized Calcium (iCa) of resp. 1.3-1.6 mg/dL (0.325-0.4 mmol/L) and 0.8-1.1 mg/dL (0.2-0.275 mmol/L). Post-filter blood as well as effluent aliquots and bloodconcentrations in the patient are tested for the following variables: