This woman has chronic hypovolemic hyponatremia as a result of diuretic use, and the hyponatremia must be corrected slowly. In cases in which hyponatremia is not life-threatening (sodium > 120 mEq/L), the goal is to replace one third of the sodium deficit over the first 12 to 24 hours and the remainder over the next 2 to 3 days. IV normal saline corrects hyponatremia because the stimulus for ADH release in this case (volume depletion) is inhibited. This patients total sodium deficit is 450 mEq/L (total body water [TBW] × [desired serum sodium - current serum sodium]), which equals approximately 3 L of normal saline
(154 mEq/L). One liter of normal saline should be given over the first 8 to 12 hours (125 mL/hr) with a subsequent infusion rate reduction. Using hypotonic saline at a slow rate is not indicated in severe hypovolemic hyponatremia. Although restriction of free water may have initially prevented the development of hyponatremia, it will not play a role in its correction or in raising blood pressure. Salt tablets, which can play a role in treatment of SIADH, would not be used for immediate treatment in this case.
- Give IV normal saline (0.9%) at 125 mL/hr.
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