Disorders of sodium metabolism: Hypernatremia and hyponatremia

Objective: Discussion of abnormal plasma sodium concentrations with an emphasis on the pathogenesis, diagnosis, and treatment. Data Sources: Relevant literature in the English language and the authors' clinical experience. Study Selection: No special study has been carried out for the present discussion. Data Extraction: The information from the literature and the data from the authors' clinical experience have been used to illustrate important points in the discussion. Data Synthesis: A most important aspect in the approach to hypernatremia is determination of the mechanism responsible for impaired water intake. Various mechanisms of abnormal water loss can be determined from measurement of urine osmolality. Hypernatremia is treated by water replacement and measures to reduce abnormal water loss. In most instances, hyponatremia is caused by inappropriate concentration of urine because of either appropriate or inappropriate antidiuretic hormone secretion. The determination of appropriateness of antidiuretic hormone secretion requires the assessment of effective arterial volume. Treatment depends on the pathogenetic mechanism. Conclusions: Abnormal plasma sodium concentration results from abnormal water intake or water output. Treatment is guided by determining the pathogenetic mechanism.