Hyponatremia

摘要

Hyponatremia is one of the most commonly encountered electrolyte disorders among both adults and children. Although childhood cases can occur in the ambulatory setting, most occur among inpatients, with the condition affecting approximately 25°/o of hospitalized children. Defined as a plasma sodium concentration less than 135 mEq/L (135 mmol/L), hyponatremia can result from either a deficit of sodium or an excess of free water. Plasma sodium concentration is the largest determinant of plasma osmolality; therefore, disturbances in sodium concentration are associated most often with disturbances in plasma osmolality. Normally, the body is able to keep plasma osmolality tightly controlled, with values ranging from 280 to 295 mOsm/kg. Homeostatic regulation is achieved through 2 important mechanisms: the thirst mechanism, which is activated in response to a salt load (and thus an increase in plasma osmolality), and the upregulation ordownre-gulation of arginine vasopressin (also known as antidiuretic hormone [ADH]) secretion.