The patient arrives in the morning to the preoperative area. A urinary analysis is taken for urinary colour, creatinine, specific weight, osmolality, microalbuminuria and electrolytes. For 30 patients a volume kinetic analysis of 5 ml/kg infusion of acetated Ringers solution is undertaken between 6.30 and 8.00 am on the morning of surgery. During 15 minutes 5 ml/kg acetated Ringers solution is infused intravenously. Hb is continuously measured noninvasively by Masimo Radical 7 pulse oximeter (MasimoHb) and invasively with maximum 13 samples a 4 ml during 80 minutes (0, 10, 15, 25, 40, 50, 60 and 70 min. Double samples at start and 60 min. The volume kinetic part of the study is finished after 70 min when the patient urinates and the volume is measured.