To assess quantitatively the evolution over time of electrolyte-free water clearance and electrolyte mass balance in patients with non-hypervolemic hypotonic hyponatremia

Achieving recommended treatment targets in management of hyponatremia is challenging: plasma sodium must be increased effectively but, at the same time, overcorrection has to be prevented. Yet, predictors of change of sodium over time have not been delineated properly. It was found, that evidence hinting to the fact that sodium baseline itself is crucial with respect to sodium evolution.

The goal of this study is to gather prospective data in order to precisely delineate the role of initial sodium levels by correlating those to plasma sodium evolution and electrolyte free water evolution. It is aimed to decipher patterns of sodium evolution with respect to anthropometric data, such as body composition analyses and blood pressure and markers of innate regulation mechanisms of body volume like aldosterone and renin. In addition, apart from these clinical aspects, a better appreciation of the physiological responses to hyponatremia treatment in terms of water and electrolyte balances is undoubtedly necessary to improve understanding of the body's mechanisms involved in osmotic homeostasis and cell volume control. Since studies to date also lack consideration of the intracellular department, the aim is to close that gap.

Inclusion Criteria:

• Adult patients ≥ 18 years

• Hypotonic hyponatremia

  • glucose-corrected plasma sodium <130 mmol/l
  • serum osmolality <280 mosmol/kg or lack of signs of non-hypotonic hyponatremia

Exclusion Criteria:

• Signs of extracellular volume expansion
• Patients with liver cirrhosis and severe liver damage AST/ALT>3xULN, AP>6xULN, Bilirubin ≥ 3mg/dl
• Patients with heart failure
• Patients on dialysis and/or patients with oliguric renal impairment and plasma creatinine ≥ 3mg/dl
• Patients after organ transplantation

Patients with non-hypervolemic hyponatremia