Water Balance: Hypo- and Hypernatremia

Serum sodium concentration is largely determined by the balance of the body’s sodium and water content. Hyponatremia results when total body water exceeds total body sodium (relative to baseline), whereas hypernatremia is the result of decreased total body water relative to sodium. Prompt recognition of these states can prevent complications in the central nervous system, such as brain edema in hyponatremic patients and cerebrovascular hemorrhages in hypernatremic patients.

Usually, diagnosis relies on thorough history-taking, a physical examination that focuses on volume assessment, and laboratory evaluation that includes serum osmolality, urine osmolality, and urine sodium concentration. The treatment of hypo- or hypernatremia depends heavily on the acuity and specific classification of the type of disturbance (e.g., hypovolemic vs. euvolemic vs. hypervolemic). The management of either condition requires regularly monitoring of serum sodium concentrations to ensure adequate treatment and to avoid potential complications.