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Electrolyte Blood Press. 2006 Nov;4(2):66-71. English. Original Article.
Kim SW .
Department of Internal Medicine, Chonnam National University Medical School, Gwangju, Korea.

Hypernatremia reflects a net water loss or a hypertonic sodium gain, with inevitable hyperosmolality. Severe symptoms are usually evident only with acute and large increases in plasma sodium concentrations to above 158-160 mmol/l. Importantly, the sensation of intense thirst that protects against severe hypernatremia in health may be absent or reduced in patients with altered mental status or with hypothalamic lesions affecting their sense of thirst and in infants and elderly people. Non-specific symptoms such as anorexia, muscle weakness, restlessness, nausea, and vomiting tend to occur early. More serious signs follow, with altered mental status, lethargy, irritability, stupor, and coma. Acute brain shrinkage can induce vascular rupture, with cerebral bleeding and subarachnoid hemorrhage. However, in the vast majority of cases, the onset of hypertonicity is low enough to allow the brain to adapt and thereby to minimize cerebral dehydration. Organic osmolytes accumulated during the adaptation to hypernatremia are slow to leave the cell during rehydration. Therefore, if the hypernatremia is corrected too rapidly, cerebral edema results as the relatively more hypertonic ICF accumulates water. To be safe, the rate of correction should not exceed 12 mEq/liter/day.

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