Renal · Year 2 · from Renal
Case 1: Heart Failure with Hyponatremia
Patient Presentation
A 72-year-old male with a history of ischemic cardiomyopathy (EF 25%) presents with worsening dyspnea, orthopnea, and lower extremity swelling over the past 2 weeks.
History of Present Illness
- Progressive dyspnea on exertion, now at rest
- Three-pillow orthopnea
- 8-pound weight gain over 2 weeks
- Lower extremity swelling
- Non-adherence to sodium and fluid restriction
- Medications: furosemide, lisinopril, carvedilol, spironolactone
Physical Examination
- Blood pressure: 98/62 mmHg
- Heart rate: 92 bpm
- JVP: 14 cm H2O (elevated)
- Bilateral crackles to mid-lung fields
- S3 gallop present
- 3+ pitting edema to knees bilaterally
Workup
Laboratory Studies:
- Serum sodium: 128 mEq/L (low)
- Serum osmolality: 268 mOsm/kg (low)
- BUN: 42 mg/dL
- Creatinine: 1.8 mg/dL (baseline 1.2)
- BNP: 1850 pg/mL (markedly elevated)
- Urine sodium: 8 mEq/L (low - sodium avid)
- Urine osmolality: 520 mOsm/kg
Diagnosis
Hypervolemic Hypotonic Hyponatremia due to Decompensated Heart Failure
Discussion
This case illustrates the concept of effective circulating volume (ECV):
- ECV vs Total Body Sodium: The lecture emphasizes that ECV may differ from total extracellular volume. Despite obvious total body sodium and water excess (edema, elevated JVP), the effective circulating volume is reduced due to poor cardiac output.
- RAAS Activation: The body responds to decreased ECV by activating RAAS, causing sodium retention that worsens edema. ADH is also elevated (non-osmotic stimulation), causing water retention and dilutional hyponatremia.
- Low Urine Sodium: Despite total body sodium excess, urine sodium is low (<20 mEq/L) because the kidneys perceive hypovolemia and avidly retain sodium.
Treatment
- IV diuretics (furosemide 80 mg IV, then continuous infusion)
- Fluid restriction (1.5 L/day)
- Sodium restriction (<2 g/day)
- Consider adding thiazide (metolazone) for diuretic resistance
- Optimize heart failure regimen
- If refractory hyponatremia: Consider tolvaptan (V2 antagonist for aquaresis)
Clinical Pearl
In heart failure with hyponatremia, the serum sodium is a marker of disease severity and prognosis. Lower sodium correlates with higher mortality. The hyponatremia is dilutional - there's too much water relative to sodium, not too little sodium.