[Dysnatremias - concepts and clinical work-up].

Osmotic gradients over cell membranes lead to water movement into or out of cells. An intact osmoregulation prevents osmotic gradients, thereby protecting cells from swelling or shrinking. Na is the major cation in the extracellular fluid (ECF) and the major determinant of the osmolarity in the ECF, including plasma. Therefore, the plasma-Na concentration needs to be tightly regulated. An excess of electrolyte-free water decreases the concentration of osmolytes leading to hyponatremia. In contrast, a free water deficit increases the osmolyte concentration leading to hypernatremia. Pathophysiology-oriented approaches to dysnatremic patients help both clinicians and patients. Therapeutic interventions depend on the differentiation between acute and chronic, asymptomatic, and symptomatic dysnatremia, and on the patient's extracellular volume status. The therapeutic armamentarium for hyponatremia consists of water restriction, hypertonic infusions, urea, V2 receptor-blockers, and sodium-glucose cotransporter 2 (SGLT2) inhibitors. Patients with hypernatremia are treated with electrolyte-free water or hypotonic sodium-containing solutions depending on their volume status. Basic concepts in the management of dysnatremic patients are discussed.