 Acute renal failure occurs in about 20 of critically ill patients and is associated with increased morbidity and mortality, in spite of modern renal replacement techniques. The latter include continuous venovenous hemofiltration CVVH techniques, necessitating anticoagulation of blood entering the extracorporeal circuit to prevent premature clot formation and hemofilter dysfunction. Heparin is commonly used for that purpose, but carries a serious risk of bleeding complications and heparin induced thrombocytopenia. In a subgroup of critically ill patients systemic anticoagulation is absolutely contraindicated. Citrate-anticoagulant CVVH carries the potential advantage of less bleeding complications and prolonged filter survival, but carries the risk of hypocalcaemia, when citrate is inappropriately or insufficiently counteracted by calcium infusion after passage of blood through the filter. In addition, when too much citrate enters the circulation, a metabolic alkalosis may develop, since citrate is converted to bicarbonate by the liver. 