Newer Insight in the Management of Hyponatremia: Role of Aquaretics/Vaptans

In hypovolemic hyponatremia, there is decrease in both total body sodium and water leading to ECF volume depletion with consequent AVP release and decreased solute-free water excretion. Clinically the patient will have tachycardia, orthostatic hypotension and loss of skin turgor. Causes of hypovolemic hyponatremia can be further classified into extrarenal and renal causes. Extrarenal causes include vomiting, diarrhea, burns, peritonitis and pancreatitis etc. Renal causes include use of thiazide diuretics, mineralocorticoid deficiency and salt wasting nephritis. Extrarenal and renal causes can be differentiated with the help of estimating urinary sodium; if urinary sodium is less than 10 mmol/L, then this point toward an extrarenal cause and if urinary sodium is more than 20 mmol/L, it points toward a renal etiology of hyponatremia. Prototype example of euvolemic hyponatremia is the syndrome of inappropriate antidiuretic hormone secretion (SIADH); in this syndrome, there is hyponatremia along with hypo-osmolarity; physical examination did not show any signs of dehydration or fluid overload; urinary osmolarity is more than 100 mOsm/L and urinary sodium is more than 25 mmol/L. But, disorders like hypoparathyroidism, hypopituitarism, and adrenal insufficiency must be ruled out before making the diagnosis of SIADH. Causes of SIADH include neoplastic, vascular, infectious and inflammatory disorders of central nervous system (CNS) and respiratory system, drugs like selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants, carbamazepine, desmo pressin and oxytocin can also cause SIADH. Causes of hypervolemic hyponatremia include cardiac failure, liver cirrhosis and nephrotic syndrome. In these conditions decreased effective arterial blood volume leads to activation of renin angiotensin aldosterone (RAAS) system and increased AVP levels leading to retention fluid in excess to sodium. Algorithm for diagnostic approach to hyponatremia is shown i