 Citrate anticoagulation Published literature data show that a mean citrate-dosage of 3.5 to 4mmoll of undiluted blood is necessary to decrease the level of ionized serum calcium below 0.4mmoll which provides sufficient anticoagulation to maintain an extracorporeal circuit. A minimum citrate concentration of 3.5 mmoll blood will be used in this protocol. The infused citrate replacement fluid contains trisodium citrate and citric acid in a mixture 10mmoll tri-sodium citrate plus 2 mmoll citric acid. Preliminary results proved that the anticoagulation potency of this mixture is similar to a plain 12 mmoll tri-sodium citrate solution. Therefore a fixed ratio of citrate replacement fluid will be infused in pre-pump predilution mode per 1 liter of effective blood flow. 