Hyponatremia

Serum sodium concentration and serum osmolarity normally are maintained under control involving stimulation of thirst, secretion of antidiuretic hormone (ADH), and renal andling of filtered sodium.

Significant hyponatremia is relatively uncommon and nonspecific in presentation; irreparable harm can occur if abnormal serum sodium levels are corrected too quickly or too slowly.

• Hypovolemic hyponatremia: Total body water (TBW) decreases, total body sodium (Na+) decreases to a greater extent. The extracellular fluid (ECF) volume is decreased.
• Euvolemic hyponatremia: TBW increases while total sodium remains normal. The ECF volume is increased minimally to moderately but without the resence of edema.
• Hypervolemic hyponatremia: Total body sodium increases, and TBW increases to a greater extent. The ECF is increased markedly, with the presence of edema.
• Redistributive hyponatremia: Water shifts from the intracellular to the extracellular compartment, with a resultant dilution of sodium. The TBW and total body sodium are unchanged. This condition occurs with hyperglycemia or administration of mannitol.
• Pseudohyponatremia: The aqueous phase is diluted by excessive proteins or lipids. The TBW and total body sodium are unchanged. This condition is seen with hypertriglyceridemia and multiple myeloma.