Abstract
Water comprises 45 to 70% of body weight, of which two thirds are intracellular and one third is extracellular. A net loss of w ater (without concomitant loss or retention of ions) will lead to serum sodium level changes.
If ions are lost together with water s erum sodi- um level may be normal in spite of dehydration/hyperhydration. Serum sodium concentration is directly proportional to exchangea ble body content of sodium and potassium, and indirectly proportional to total body water.
Total body content of sodium can only be esti- mated with respect to these variables. Normovolemia, hypovolemia as well as hypervolemia may be accompanied by normo-, hypo- or hypernatremia.
Accordingly, there are eight types of water and sodium dysbalance, of various pathogenesis, clinical importance, and treatment modalities. As an aid to quantitative corrections of these states, several simple formulas have been suggested but du e to rather complicated relations between water and electrolyte exchange they only serve as a rough guide.
In parallel with administ ration of the calculated volume and composition of the infusion (or with water and salts restriction) it is necessary to monitor frequ ently the changes in body fluids composition, and to modify the treatment accordingly. While correcting the fluid and electrolyte dysbala nces, also the suggested rate of changes should be kept in mind, particularly with regard to extracellular fluid tonicity changes tha t are clo- sely related to water content in the cells of central nervous system.