[Hypernatremia in neurosurgical pathology].

Hypernatraemia is defined as an increase in extracellular sodium concentration, associated with plasma hyperosmolality and cellular dehydration. It can result from excessive water loss, from an increase in the total sodium content or from both mechanisms. As far as neurosurgical pathology is concerned, hypernatraemia due to excessive water loss may be observed in patients who do not sense thirst or are unable to ingest water. Urinary water loss is seen in diabetes insipidus and osmotic diuresis. Extrarenal water losses from pulmonary origin may be observed in intubated or tracheotomized patients. Hypernatraemia with sodium and water retention may be encountered in patients suffering from Cushing diseases or syndromes, or more frequently in those who are given excessive amounts of sodium (hypertonic saline, sodium salts). Clinical manifestations of hypernatraemia consist of neurologic symptoms related to cellular dehydration; their severity is correlated with the rapidity of the onset of the electrolytic disorder. Depending on the pathophysiological mechanism, treatment of hypernatraemia involves stopping sodium intake, restoring normovolaemia and administering hypotonic fluids. Treatment of diabetes insipidus relies on the administration of the antidiuretic hormone and of drugs that increase its secretion rate or its responsiveness in the kidneys.