Hypotonic Hyponatremia: Diagnosis and Management

The diagnosis and treatment of hyponatremia present challenges to clinicians and opportunities to improve our understanding of body water, sodium and potassium homeostasis and disorders. The first step in the diagnosis of every case of hyponatremia is to categorize it as hypotonic hyponatremia, hypertonic hyponatremia, or pseudohyponatremia. The diagnostic steps that follow the verification of hypotonic hyponatremia include: (a) the identification of the medical condition that caused the hyponatremia; (b) the evaluation of the mechanism of hyponatremia, including the computation of the magnitude of the changes in body water, sodium, and potassium that were responsible for the hyponatremia. Whether the extracellular volume is low, normal, or high provides key information for the determination of the mechanism of hyponatremia and the choice of its treatment method; and (c) the determination of the duration of hyponatremia. Whether hyponatremia is acute or chronic (i.e., lasting more than 48 h) has important implications for its manifestations and management. This perspective reviews the diagnostic categories and various aspects of treatment strategies of hypotonic hyponatremia, including choosing the method(s) for increasing the electrolyte-free renal water clearance, decreasing this clearance during treatment to prevent excessively rapid correction of hyponatremia, determining the type and amount of saline infused for correction of the hyponatremia (choice of isotonic versus hypertonic saline and of the target rise in serum sodium, which determines, along with other parameters, the volume of saline infused), and dialytic methods for correcting hyponatremia. The aim of this perspective is to identify topics that require further research, including diagnostic topics and treatment areas.