title: [A new concept to explain dysnatremia: the tonicity balance of entries and exits].
abstract: Plasma sodium concentration, or natremia, results from three main factors: exchangeable sodium (Na+), exchangeable potassium (K+) and total body water (H2O). Its alterations often imply a change in cell volume. Understanding dysnatremias is essential for the treatment and prevention of hydromineral disorders. Extra-cellular fluid tonomoles consist almost exclusively of Na+ salts. Their dilution is the tonicity. K+ is an essential tonomole for intra-cellular fluid tonicity. The balance between intra and extracellular tonicities depends on water movements and is responsible for changes in intra- and extracellular fluid volumes. Cell volume is therefore depending on the tonicity balance. A change in body tonicity (which is not osmolality) can be correctly and rapidly appreciated by measuring the (Na+ + K+) and H2O balances. Clinical cases emphasize the misleadings resulting from the free-water clearance calculation or the only measurements of urinary losses. They also demonstrate that tonicity balance provides indications for therapy whereas analyses based upon electrolyte-free water do not. Intakes should be quantified with the same care than losses. The units used must be coherent to allow a quick and easy understanding at the bedside. Tonicity balance should be taught and Na+ + K+ and H2O balances should be routinely utilized by practitioners, dieticians and nurses in the concerned pediatrics, in particular intensive care, internal medicine, nephrology, pediatry and anesthesiology.
authors.affiliation: Hôpital d'Enfants-CHU de Nancy-Rue de Morvan-54511 Vandoeuvre, France.
authors.forename: J P
authors.initials: JP
authors.lastname: Mallié
authors.forename: M L
authors.initials: ML
authors.lastname: Halperin
mesh_terms: D000293:Adolescent; D000328:Adult; D004573:Electrolytes / Q000378:metabolism; D005260:Female; D006801:Humans; D006955:Hypernatremia / Q000378:metabolism*; D007010:Hyponatremia / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D004573:Electrolytes; D014867:Water; D012964:Sodium; D011188:Potassium