A 52-year-old female (weight 74 kg) in the ICU has hypernatremia due to excessive free-water losses. Medical history: bipolar disorder and chronic lithium use; mild renal dysfunction (serum creatinine 1.4 mg/dL); no hepatic dysfunction. Current medications: lithium carbonate 300 mg PO twice daily, quetiapine 100 mg PO nightly. Labs: serum sodium 158 mEq/L (135–145), glucose 100 mg/dL (70–100), BUN 22 mg/dL (7–20). Which therapeutic intervention is indicated based on the osmolarity calculation and suspected nephrogenic diabetes insipidus?
- Initiate desmopressin and restrict free water
- Hold lithium and consider starting a thiazide diuretic to reduce polyuria (correct answer)
- Administer 3% sodium chloride to correct sodium rapidly
- Add sodium bicarbonate infusion to lower serum osmolality
Explanation: This question tests management of hypernatremia due to nephrogenic diabetes insipidus from chronic lithium use. The patient's hypernatremia (158 mEq/L) and history of lithium therapy suggest lithium-induced nephrogenic diabetes insipidus, where kidneys cannot concentrate urine despite ADH. Holding lithium and considering a thiazide diuretic is correct because thiazides paradoxically reduce polyuria in diabetes insipidus by causing mild volume depletion and enhancing proximal tubule water reabsorption. Desmopressin (option A) won't work in nephrogenic DI as kidneys don't respond to ADH, 3% saline (option C) would worsen hypernatremia, and sodium bicarbonate (option D) is not indicated. The clinical pearl is that thiazide diuretics, despite typically causing increased urination, can reduce urine output in diabetes insipidus through compensatory mechanisms when combined with sodium restriction.