1. The distribution and elimination of infusion fluids can be studied by volume kinetics, a mathematical method based on serial analysis of the blood hemoglobin concentration.
2. The hypothesis of the present study is that the elimination of infused fluid is retarded in the presence of dehydration, and that volume kinetics would therefore be capable of detecting dehydration in human subjects.
3. We induce dehydration by injection graded doses of furosemide (a diuretic drug) in healthy volunteers and the kinetics of an infusion of crystalloid fluid is compared to when the same volunteer receives the same fluid without being in a dehydrated state.

1. Fifteen healthy male volunteers are subjected to 4 experiments. They drink 800 ml of water at 6:00 AM to make sure they are not dehydrated when the experiments begin.
2. On two occasions the volunteer receives, at 9:00 AM, an intravenous infusion of acetated Ringer´s solution being either 5 ml/kg or 10 ml/kg, over 15 min. The blood hemoglobin concentration is measured during 16 occasions during 120 min by invasive blood sampling and also non-invasively by a pulse oximeter (Masimo´s Radical 7).
3. On two other occasions, the infusions are preceded for 2 hours of deliberate dehydration. Doses of furosemide 5 mg are repeated 3-4 times with the goal of creating dehydration amounting to approximately 2 liters of fluid. Excreted urine is collected and the volume measured.
4. The kinetics of each infusion is calculated by volume kinetics, and the data compared pairwise from the experiments with and those without dehydration.
5. The accuracy and precision of the non-invasive monitoring of Hgb can be determined.
6. The study is ended with that the Hgb response between the lying and sitting position is compared and with that the fluid balance is restored by ingestion of water.
7. Experiments are performed in the Department of Intensive Care at Linköping University Hospital, Sweden.

Inclusion Criteria:

• Healthy male.

Exclusion Criteria:

• Disease for which daily medication is required.
• Poor peripheral perfusion; defined as a perfusion index, as measured by Masimo´s Radical 7, of 2 or less.