What are the causes and management of hyponatremia?

Causes and Management of Hyponatremia

The management of hyponatremia must be tailored to its specific etiology (hypovolemic, euvolemic, or hypervolemic) and severity, with careful attention to the rate of correction to prevent osmotic demyelination syndrome. 1

Classification and Causes of Hyponatremia

Hyponatremia is defined as serum sodium concentration less than 135 mEq/L, with severity classified as:

• Mild: 126-135 mEq/L
• Moderate: 120-125 mEq/L
• Severe: <120 mEq/L 1

Based on Volume Status:

1. Hypovolemic Hyponatremia

   • Excessive diuretic use
   • Gastrointestinal losses (vomiting, diarrhea)
   • Poor oral intake
   • Third-space losses (burns, pancreatitis)
   • Renal losses (salt-wasting nephropathies)

2. Euvolemic Hyponatremia

   • Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
   • Medications (e.g., sertraline, carbamazepine)
   • Severe hypothyroidism
   • Adrenal insufficiency
   • Reset osmostat syndrome

3. Hypervolemic Hyponatremia

   • Liver cirrhosis
   • Congestive heart failure
   • Nephrotic syndrome
   • Renal failure 1, 2

Pathophysiology in Cirrhosis

In liver cirrhosis, hyponatremia results from:

• Systemic vasodilation due to portal hypertension
• Decreased effective plasma volume
• Activation of renin-angiotensin-aldosterone system
• Inappropriate antidiuretic hormone regulation
• Increased arterial natriuretic peptide
• Decreased prostaglandin E2
• Decreased degradation of antidiuretic hormone 1

Clinical Manifestations

Symptoms depend on severity and rapidity of onset:

• Mild symptoms: Nausea, muscle cramps, headache, weakness, cognitive impairment
• Severe symptoms: Confusion, delirium, seizures, coma, respiratory distress 1, 2

Even mild chronic hyponatremia is associated with:

• Cognitive impairment
• Gait disturbances
• Increased falls and fractures
• Osteoporosis 2

Management Approach

Step 1: Assess Chronicity and Severity

• Acute hyponatremia (onset <48 hours): More aggressive correction is acceptable
• Chronic hyponatremia (onset >48 hours): Requires more gradual correction 1

Step 2: Treat Based on Volume Status and Severity

Hypovolemic Hyponatremia:

• Treatment: Discontinue diuretics and correct dehydration
• Fluid choice: 0.9% saline or 5% IV albumin (preferred in cirrhosis)
• Monitor: Serum sodium levels frequently 1

Euvolemic Hyponatremia:

• Treatment: Address underlying cause (e.g., medication adjustment)
• Fluid restriction: 1,000 mL/day for moderate hyponatremia
• Consider: Salt tablets or vasopressin receptor antagonists in appropriate cases 1, 2

Hypervolemic Hyponatremia:

1. Mild (126-135 mEq/L):

   • Monitor serum sodium
   • Water restriction if needed

2. Moderate (120-125 mEq/L):

   • Fluid restriction to 1,000 mL/day
   • Discontinue IV fluid therapy
   • Consider albumin infusion

3. Severe (<120 mEq/L):

   • More severe fluid restriction
   • Albumin infusion
   • Consider vasopressin receptor antagonists in selected cases 1

Step 3: Rate of Correction

• Maximum correction rate: 8-10 mEq/L in 24 hours
• Target correction rate: 4-8 mEq/L per day for average risk
• High-risk patients (advanced liver disease, alcoholism, malnutrition): 4-6 mEq/L per day 1

Special Considerations

Severely Symptomatic Hyponatremia

For patients with severe symptoms (seizures, coma):

• Administer 3% hypertonic saline
• Target increase: 4-6 mEq/L within 1-2 hours
• Do not exceed 10 mEq/L in first 24 hours
• Monitor sodium levels frequently 2

Osmotic Demyelination Syndrome (ODS)

• Risk factors: Chronic hyponatremia, liver disease, alcoholism, malnutrition
• Symptoms: Dysarthria, dysphagia, quadriparesis, altered mental status
• Prevention: Avoid correction >10 mEq/L in 24 hours
• If overcorrection occurs: Consider relowering with electrolyte-free water or desmopressin 1

Vasopressin Receptor Antagonists (Vaptans)

• Mechanism: Selective V2 receptor blockade
• Indications: Selected cases of hypervolemic or euvolemic hyponatremia
• Cautions:
  • Start in hospital with close monitoring
  • Avoid in patients with altered mental status
  • Monitor for drug interactions (CYP3A inhibitors/inducers)
  • Risk of gastrointestinal bleeding in cirrhosis 1, 3

Monitoring and Follow-up

• Frequent serum sodium measurements (every 2-4 hours initially in severe cases)
• Monitor fluid status
• Adjust treatment based on rate of correction
• Continue monitoring after normalization to prevent hypernatremia 1