 Main objective: Investigation of the mortality during continuous venovenous hemofiltration with systemic anticoagulation with heparin compared with regional anticoagulation with trisodium citrate and also the investigation of the filter survival. Our hypothesis is, that regional citrate anticoagulation with replacement solution containing trisodium citrate, will be associated with less bleeding complications compared to heparin, with also a better filter survival. Most important we want to evaluate the hypothesis that treatment with citrate will result in a lower mortality compared to treatment with systemic heparinization. 