Plasma Sodium and Sodium Administration in the ICU

Inclusion Criteria: * Adult * Documented length of stay at the Central Intensive Care Unit (CIVA) at the University Hospital of Linköping of seven (7) days minimum. * The patient has been discharged from the ICU. * Body Mass Index (BMI) between 18.0 and 48.0 kg/m2 at admission. Exclusion Criteria: * The patient has previously been included in the study in connection with another ICU-admission. * The patient has a severe hyponatremia (\<129 mmol/L) upon arrival to the ICU. * The patient has a severe hypernatremia (\>149 mmol/L) upon arrival to the ICU. * The patient is severely hyperosmolar (\>330 mmol/L) upon arrival to the ICU. * The patient is severely hyperglycemic (\>30 mmol/L) upon arrival to the ICU. * The patient has an elevated serum urea (\>30 mmol/L) upon arrival to the ICU. * The patient receives any dialysis treatment during the observation time. * The patient is suspected to have an elevated intracranial pressure during the observation time or is suspected to have other intracranial pathology that is likely to affect sodium homeostasis * The patient has an intoxication with toxic alcohols as a primary diagnosis.