Hyponatremia in a Patient with Heart Failure and CKD
A 72-year-old man with heart failure with reduced ejection fraction (EF 30%) and stage 4 CKD (baseline eGFR 25 mL/min/1.73 m²) is admitted with dyspnea and edema. He takes furosemide 80 mg daily, carvedilol 6.25 mg BID, sacubitril/valsartan 24/26 mg BID, spironolactone 12.5 mg daily, and empagliflozin 10 mg daily. Labs: Na 124 mEq/L, K 4.8 mEq/L, Cl 94 mEq/L, HCO3 22 mEq/L, BUN 45 mg/dL, creatinine 2.8 mg/dL, glucose 110 mg/dL, serum osmolality 265 mOsm/kg. Urine osmolality 420 mOsm/kg, urine Na 18 mEq/L. He is euvolemic on exam with mild pedal edema. He is alert and oriented.
1. What is the most likely cause of his hyponatremia, and how would you initially manage it?
Read the worked answer
The patient has hypotonic hyponatremia (serum osmolality 265 mOsm/kg) with urine osmolality >100 mOsm/kg and urine Na >30 mEq/L? Actually urine Na is 18 mEq/L, which is low. In heart failure, effective arterial volume depletion leads to ADH release and low urine Na due to avid sodium retention. However, the low urine Na (<20 mEq/L) suggests volume depletion, but he has heart failure and edema. The use of sacubitril/valsartan (ARNI) and spironolactone can contribute to hyponatremia. The most likely cause is hypervolemic hyponatremia due to heart failure with reduced effective circulating volume, compounded by diuretics and ARNI. Initial management: fluid restriction (1-1.5 L/day), continue diuretics for congestion, consider tolvaptan? But tolvaptan is not recommended in heart failure with volume depletion? Actually, tolvaptan is FDA-approved for euvolemic and hypervolemic hyponatremia, but in heart failure it has not shown mortality benefit. The key is to treat the underlying heart failure and congestion. Also, review medications: thiazide? Not on. SSRIs? No. The low urine Na suggests that the hyponatremia is not due to SIADH (which typically has urine Na >30). In heart failure, urine Na is usually low due to aldosterone activation. So management: fluid restriction, optimize heart failure therapy, consider increasing loop diuretic if congested. Avoid rapid correction. Monitor sodium. If symptomatic, hypertonic saline? He is asymptomatic. So fluid restriction and treat heart failure.
2. If his serum sodium remains 124 mEq/L after 48 hours of fluid restriction, what pharmacologic option would you consider and why?
Read the worked answer
After fluid restriction fails, consider tolvaptan, a vasopressin V2 receptor antagonist. It is approved for euvolemic and hypervolemic hyponatremia. However, in heart failure, the EVEREST trial showed no improvement in long-term outcomes, but it can increase serum sodium. Use with caution due to risk of rapid correction and liver toxicity. Alternatively, urea? Not standard. Another option is increasing loop diuretic to promote free water clearance, but loop diuretics can worsen electrolyte imbalances. The patient has CKD stage 4, so tolvaptan may be used with monitoring. The goal is to raise sodium by <8-10 mEq/L in 24 hours to avoid osmotic demyelination. Start tolvaptan 15 mg daily and monitor sodium closely. Also, consider whether sacubitril/valsartan contributes; if hyponatremia persists, may need to adjust. But the question asks for pharmacologic option: tolvaptan.