Systematic Use of DDAVP to Prevent Serum Sodium Overcorrection in Severe Hyponatremia

Inclusion Criteria: * Adults ( ≥18 years) * Current admission in ICU * Severe hyponatremia defined by SNa \<120 mmol/L in the presence of neurological symptoms (seizures, stupor defined as Glasgow score \< 12, or signs of brain herniation) or by SNa \<115 mmol/L * Normal or decreased extracellular fluid volume Exclusion Criteria: * Obvious increase of extracellular fluid volume (cirrhosis with ascites, congestive heart failure, nephrotic syndrome); * Hyponatremia caused by hyperglycaemia (\> 30 mmol/L) or hypertriglyceridemia (10 g/L) or hyperproteinaemia (120 g/L) * Severe acute kidney injury (KDIGO 3) * Severe chronic kidney disease (eGFR \<20 ml/min) * Coronary patients well stabilized with trinitrine-based medicines * Recent neurosurgery or traumatic brain injury * Previous DDAVP or hypertonic fluid administration for the current episode of severe hyponatremia * SNa increased by 5 mmol or more between admission at hospital and randomisation (H0) * Known contraindication to DDAVP * Allergy * Syndrome of inappropriate antidiuretic hormone secretion (SIADH) * History of unstable angina and/or known or suspected heart failure. * Willebrand disease type IIB * Severe previous neurologic disability (Glasgow Outcome Scale: GOS \< 3) * Diabetes insipidus receiving DDAVP treatment * Moribund state (patient likely to die within 24h) * Need for invasive mechanic ventilation * Enrolment to another interventional study (clinical trial on medicinal product, medical device and interventional research involving human participants not concerning health product) * Pregnancy or breastfeeding * Subject deprived of freedom, subject under a legal protective measure * No affiliation to any health insurance system * Refusal to participate to the study (patient or legal representative or family member or close relative if present)