• Clinical science

Sodium disorders


Sodium is the most important extracellular cation and plays an important role in maintaining the body's extracellular fluid volume. Sodium imbalances typically reflect a dilution or concentration of extracellular fluid rather than an actual loss or gain of sodium. These changes in extracellular fluid volume are mainly due to an increase or decrease in ADH serum levels (which causes the retention and loss of free water respectively). In certain cases, however, sodium imbalances may be the direct result of sodium loss (e.g., following diarrhea, vomiting, or the use of antidiuretics) or excessive sodium intake. Treating sodium imbalances involves careful correction of the sodium deficit/excess and treating the underlying cause. A rapid correction of sodium imbalance can have damaging osmotic effects such as central pontine myelinolysis.





Hypotonic hyponatremia (↓ serum osmolality)

Isotonic hyponatremia (↔︎ serum osmolality)

Hypertonic hyponatremia (↑ serum osmolality)

  • Hyperglycemia
  • Use of mannitol
  • Aldosterone
  • ADH
    • Effect: ADH causes water reabsorption and increases thirst.
    • Release of ADH
      • Primary stimulus: increase in serum osmolality (very sensitive even to a 1% change in serum osmolality).
      • Non-osmotic stimulus: A change in extracellular fluid volume by more than 10% (which is sensed by carotid baroreceptors) can also stimulate ADH release.


Hypovolemic hypernatremia

Euvolemic hypernatremia

Hypervolemic hypernatremia


Clinical features

  • Clinical features are primarily neurological and depend on the severity of the sodium imbalance.
    • Mild symptoms
    • Moderate symptoms
      • Muscle weakness
      • Lethargy
      • Confusion
    • Severe symptoms
  • Symptoms also depend on the onset of sodium imbalance
    • Acute onset (< 48 hours): usually symptomatic event even with mild sodium derangements
    • Subacute or chronic onset (> 48 hours): usually asymptomatic unless severe derangements are present



  • Blood tests
  • Urine examination
    • Hyponatremia: urine sodium concentration
      • > 20 mEq/L implies renal sodium loss
      • < 20 mEq/L implies extrarenal sodium loss
    • Hypernatremia: urine osmolality
      • > 800 mOsmol/kg implies extrarenal water loss
      • < 800 mOsmol/kg implies renal water loss The kidneys continue to excrete water despite a water deficit.



General principles

  • Treat underlying cause
  • Patients with serum sodium values < 120 mEq/L or >160 mEq/L require intensive care.
  • Careful correction of sodium levels: maximum correction within 24 hours is 10 mEq/L (rate of correction: 0.5–1 mEq/L per hour)


  • Hypovolemic hyponatremia
    • Mild to moderate symptoms: normal saline
    • Severe symptoms: hypertonic saline
  • Euvolemic hyponatremia
    • Mild to moderate symptoms: fluid restriction
    • Severe symptoms: hypertonic saline
  • Hypervolemic hyponatremia:
    • Mild to moderate symptoms: fluid restriction ± loop diuretic
    • Severe symptoms: isotonic saline


The cornerstone of the management of hypernatremia is correcting the free water deficit.

Slow correction to prevent osmotic cell damage!



Osmotic myelinolysis

The symptoms of pontine myelinolysis appear 2 to 6 days after the correction of hyponatremia!



We list the most important complications. The selection is not exhaustive.