 Ringer group conventional group: Ringers acetate solution Ringer-acetate, Baxter; pH 6.0, contents Na 131 mmolL, Cl- 112 mmolL, acetate 30 mmolL The trial will end after the first 24 hours of ICU treatment or when the patient leaves the ICU if the latter occurs within the first postoperative 24 hours. After the study period, fluids are administered according to the local clinical practice. 