The treatment of hyponatremia is aimed at addressing the underlying cause of the condition and replenishing the blood sodium levels, without causing the blood to become too dilute.

Depletional hyponatremia and dilutional hyponatremia

Depletional hyponatremia refers to reduced levels of fluid and salt, as seen in cases of gastrointestinal loss due to recurrent vomiting or diarrhea, for example. A hyponatremic state can also be caused by blood becoming too dilute (dilutional hyponatreamia). This can be caused by the administration or intake of too much fluid. Another cause is the excessive release of antidiuretic hormone by the pituitary gland, referred to as syndrome of inappropriate antidiuretic hormone (SIADH).

Treatment outline for hyponatremia

• If the condition is moderate and due to poor diet or drinking too much water, for example, the patient may be advised to cut back on fluids and change their diuretic intake.
• A more severe, acute form of the condition, will require more aggressive treatment such as intravenous fluids or medication.

• In the case of hyponatremia that is not acute, the blood sodium level is corrected slowly. The underlying cause of the lowered sodium level is to be corrected first, if possible. It is important the sodium level is adjusted gradually since rapid correction can lead to a higher risk of central pontine myelinolysis (CPM), also known as osmotic demyelination syndrome. The symptoms of this condition include dysphagia, pain in the joints or dysarthria, seizures, confusion, loss of consciousness and paralysis of all four limbs. These symptoms typically start 1-3 days after plasma sodium has been corrected too quickly.
• In patients who develop symptoms and have a blood sodium level of less than 125 mmol/l, treatment is necessary.
• If the cause of the hyponatremia is SIADH, fluid intake needs to be restricted. To control the activity of ADH, certain medications may be used such as demeclocyline, urea or vaptans.

Treatment of depletional hyponatremia

• The underlying cause of fluid and sodium loss is corrected
• The oral intake of fluids with electrolytes (using oral rehydration solution ORS) is encouraged, according to thirst levels
• If necessary, intravenous fluids with sodium chloride 0.9% is given
• Serum sodium concentration is checked at least every 2 to 4 hours to prevent rapid correction

Treatment of dilutional hyponatremia

• Fluid is restricted to less than 1 litre per day, depending on severity
• Medications and hypotonic fluids (with sodium less than 0.9%) are reviewed and stopped if necessary
• The target is to increase sodium levels by 0.5 to 1.0 mmol/l every hour, to a maximum of 12 mmol/l in a 24-hour period
• Serum sodium concentration is checked at least every 2 to 4 hours to prevent rapid correction
• Hypertonic sodium chloride solution needs to be given only in rare cases