Brief Summary: A short bolus infusion of fluid, called "fluid challenge" is commonly recommended for fluid treatment during longer surgery. However a prolonged increase of the blood volume is a prerequisite to recommend the technique. The purpose with the study is to examine the plasma expanding effect of three different fluid challenge strategies (acetated Ringers 4 ml/kg body weight, albumin 5% 4 ml/kg body weight or albumin 20% 1 ml/kg body weight), using hemoglobin as a dilution indicator.

Detailed Description: 60 patients scheduled for laparoscopic abdominal surgery, with a duration exceeding 90 minutes will be included in the study. These are randomized to three different groups (20 in each groups): The first group of patients will receive boluses of acetated Ringers 4 ml/kg body weight. The second albumin 4 ml/kg body weight and the third group albumin 20% 1 ml/kg body weight. Hemoglobin, albumin and colloid osmotic pressure (COP) is sampled the day before surgery and in the morning directly prior to the anesthesia. Bioimpedance, urine osmolality and urine-creatinin are also measured. After induction of surgery a Cardio Q probe is inserted threw the nose into the esophagus, for circulatory measurements. Initial/baseline blood samples are taken after insufflation of carbon dioxide to the abdomen. Before every bolus of fluid and 5, (10), 15, 20, 30, 40, (50) and (60) minutes new blood samples are taken for determination of hemoglobin, albumin and COP. Artery blood gases are sampled 15 minutes after every infusion or depending on the clinical need.