How is hypervolemic hyponatremia managed?
Unlike hypovolemic hyponatremia, the mainstay of therapy for hypervolemic hyponatremia arising from either heart failure or cirrhosis is water restriction. Loop diuretics can also be effective in hyponatremia associated with heart failure. By inhibiting sodium reabsorption in the ascending limb of the Loop of Henle, loop diuretics decrease the tonicity of the medulla and thereby diminish the driving force for ADH-mediated water reabsorption in the collecting duct. (By acting in the distal tubule of the cortex, thiazide diuretics block sodium reabsorption only at a site where sodium is reabsorbed without water. Moreover, generation of a hypertonic medullary interstitium is unaffected, leaving conditions persistently favorable for electrolyte-free water reabsorption. Thus, thiazide diuretics tend to induce hyponatremia .) When water restriction and loop diuretics fail, a vasopressin receptor antagonist (vaptan) may be useful. Conivaptan (a non-selective V1/V2 antagonist) and tolvaptan (a pure V2 antagonist) can be used to promote aquaresis in volume-overloaded heart failure patients with mild-to-moderate symptomatic hyponatremia. Conivaptan should be used with caution in patients with cirrhosis due to a theoretically increased risk for hypotension or variceal bleeding via antagonism of the V1 pressor receptor. Tolvaptan is relatively contraindicated in patients with cirrhosis as well due to the possibility of hepatotoxicity. More common side effects associated with these medications include thirst and dry mouth.