A low blood sodium level is known as hyponatremia and is defined as a sodium level of less than 136 millimoles per litre (mmol/L). Diarrhea, diuretics, heart failure and renal disease are common causes, and the specific aetiology may be determined by examining the plasma and urine electrolyte levels. The direct treatments for hyponatremia generally involve reducing the water intake and increasing its loss. Hyponatremia may also be corrected by treating the underlying cause.
Treat mild hyponatremia with dietary adjustments. Mild hyponatremia is a blood sodium level greater than 120 mmol/L and is usually treated by eliminating the intake of any diuretics. Some patients may also require sodium or potassium replacement.
Treat hyponatremia that is accompanied by low blood volume (hypovolemia). Both conditions can usually be corrected by administering a solution of 0.9% saline. A blood sodium level of less than 120 mmol/L may also require the water intake to be restricted to less than one litre per day.
Treat hyponatremia in patients with high blood volume (hypervolemia). This combination of conditions is typically caused by diseases such as cirrhosis, heart failure and nephrotic syndrome. These patients may require escalating doses of diuretics if intravenous saline is ineffective.
Treat severe hyponatremia when the blood volume is normal (euvolemia). The treatment for these conditions should be directed towards the underlying causes, such as adrenal insufficiency, hypothyroidism and diuretic use. A severe restriction of water of less than a half-litre per day may also be necessary.
Treat severe hyponatremia. A sodium level of less than 109 mmol/L should be treated with a stringent restriction of water intake. The specific rate of sodium level increase is controversial but should be limited to less than 10 mmol/L in the first 24 hours.