endocrine and metabolic disorders
Hyponatremia
Introduction
Hyponatremia is decrease in serum sodium concentration<136 mEq/L (<136 mmol/L) caused by an excess of water relative to solute. Common causes include diuretic use, diarrhea, heart failure, liver disease, renal disease, and the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Clinical manifestations are primarily neurologic (due to an osmotic shift of water into brain cells causing edema), especially in acute hyponatremia, and include headache, confusion, and stupor; seizures and coma may occur. Diagnosis is by measuring serum sodium. Serum and urine electrolytes and osmolality and assessment of volume status help determine the cause. Treatment involves restricting water intake and promoting water loss, replacing any sodium deficit, and correcting the underlying disorder. (See also Water and Sodium Balance .) 