Sodium

Sodium (Na⁺) is the major extracellular cation and the primary determinant of plasma osmolality. It plays a critical role in maintaining fluid balance, nerve impulse transmission, and muscle contraction. Serum sodium reflects the ratio of total body sodium to total body water.

• Sodium abnormalities affect neurological function (confusion, seizures, coma)
• Rapid correction of chronic hyponatremia can cause osmotic demyelination syndrome
• Rapid correction of hypernatremia can cause cerebral edema
• Always assess volume status when evaluating sodium disorders

• Hyponatremia = too much water relative to sodium (dilutional)
• Hypernatremia = too little water relative to sodium (concentrational)
• Assess: Is patient hypovolemic, euvolemic, or hypervolemic?
• Check urine osmolality and urine sodium to determine cause