Changes in hospital routine made enrolement difficult.

Hyponatremia (serum sodium of less than 135 mmol/L)is a very common electrolyte disorder. The reasons for the disorder varies as well as if it is acute or chronic.

In this study we wish to follow changes in colloid osmotic pressure and osmolality during the initial treatment hours. We also wish to use mass balance for the calculation of body compartments and to detect fluid translocation between these.

Patients with hyponatremia arriving att the intensive care unit are asked to participate in the study. The first blood samples are collected before initializing the treatment as well as measurements of body compartments with a bioimpedance analyzer. Collected blood samples are electrolytes (Sodium, Potassium and Chloride), colloid osmotic pressure, osmolality and hemoglobin. These samples are repeated at 4 and 8 hours after start of the study. Amount of infused fluid as well as electrolytes are recorded. Urine volume is measured and urine samples are analyzed for the loss of electrolytes.

Additional samples for guidance of treatment are collected every hour.

Hopefully the addition of colloid osmotic pressure, osmolality and mass balance can be beneficial in the diagnosis of the reason for the disorder as well as for the treatment.

Inclusion Criteria:

• Patients treated for Hyponatremia at the intensive care unit.

Exclusion Criteria:

• Circulatory instable patients in need of treatment for more than the hyponatremia.

All patients treated for severe hyponatremia, at the intensive care unit.