Hypervolemic Hyponatremia (Type B)
In hepatorenal syndrome with low albumin and sodium, the hyponatremia is hypervolemic (dilutional), not hypovolemic or euvolemic. 1, 2
Pathophysiology in Hepatorenal Syndrome
Hepatorenal syndrome occurs in advanced cirrhosis with portal hypertension, creating a specific pattern of fluid and sodium imbalance:
- Systemic vasodilation in the splanchnic circulation leads to decreased effective plasma volume despite total body fluid overload 3
- Non-osmotic hypersecretion of vasopressin occurs due to perceived arterial underfilling, causing excessive water retention 1, 2
- Enhanced proximal nephron sodium reabsorption through activation of the renin-angiotensin-aldosterone system leads to sodium and water retention 2
- Impaired free water clearance results in dilutional hyponatremia, affecting approximately 60% of cirrhotic patients 2
Clinical Characteristics Supporting Hypervolemic Classification
The combination of hepatorenal syndrome with low albumin creates a hypervolemic state characterized by:
- Ascites - fluid accumulation in the peritoneal cavity from portal hypertension and low oncotic pressure 1, 3
- Peripheral edema - total body sodium and water excess despite low serum sodium 2
- Low serum albumin - decreased oncotic pressure contributing to third-spacing of fluid 3
- Elevated total body sodium with paradoxically low serum sodium concentration due to proportionally greater water retention 1, 2
Diagnostic Confirmation
To confirm hypervolemic hyponatremia in this setting:
- Urine sodium typically >20 mmol/L despite sodium retention, reflecting the kidney's attempt to excrete excess sodium 2
- Urine osmolality >300-500 mOsm/kg indicating impaired free water excretion 1
- Physical examination reveals ascites, peripheral edema, and signs of volume overload 2, 4
- IVC ultrasound may show IVC-CI <20% and IVCmax >0.7 cm, confirming intravascular hypervolemia 4
Why Not the Other Options
Not hypovolemic (Option C): Despite activation of volume-sensing mechanisms, patients have total body sodium and water excess with ascites and edema, not true volume depletion 1, 2, 3
Not euvolemic (Option A): The presence of ascites and edema clearly indicates hypervolemia, not euvolemia 2
Not pseudohyponatremia (Option D): This is true hypotonic hyponatremia with low serum osmolality, not artifact from hyperlipidemia or hyperproteinemia 5, 6
Management Implications
Recognizing this as hypervolemic hyponatremia is critical because treatment differs fundamentally:
- Fluid restriction to 1000-1500 mL/day is first-line therapy for sodium <125 mmol/L 1, 2
- Albumin infusion may improve serum sodium concentration in cirrhotic patients 1, 2
- Avoid hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 1, 2
- Temporarily discontinue diuretics if sodium <125 mmol/L 2
- Correction rate must not exceed 4-6 mmol/L per day (maximum 8 mmol/L in 24 hours) due to high risk of osmotic demyelination syndrome in liver disease 1, 2, 5