Abstract
Hyponatremia (decreased serum Na+ bellow low limit of a laboratory method – usually 135–137 mmol/l) is frequent abnormality. Even asymptomatic, hyponatremia is linked with increased morbidity and mortality.
Correct diagnosis is based on evaluation of serum osmolality and tonicity, volume of extracellular fluid and concentration of Na+ in urine. Acute severe hyponatremia (<120 mmol/l) must be treated with hypertonic saline immediately.
Chronic hyponatremia should be treated with respect on its type (hypo-, eu- and hypervolemic hyponatremia) and cause. Rapid correction of chronic hyponatremia can lead to osmotic brain demyelination.
If hypervolemic hyponatremia (chronic heart failure, liver cirrhosis and nephrotic syndrome) is excluded, one half of cases of hyponatremia are caused by SIADH (syndrome of inappropriate antidiuretic hormone secretion). Therapy of SIADH is based on fluid restriction.
If this is not effective or is not tolerated by patient, vaptans (vasopressin V2 receptor antagonists in kidneys) can be used.