What are the dangers of hyponatremia and how is it treated?

Dangers of Hyponatremia and Treatment Approach

Hyponatremia (serum sodium <135 mmol/L) is a potentially life-threatening electrolyte disorder that can cause significant morbidity and mortality, with treatment generally indicated when levels fall below 130 mmol/L. 1

Dangers of Hyponatremia

Acute Complications

• Severe symptoms (serum sodium <125 mmol/L):
  • Cerebral edema
  • Seizures
  • Altered mental status
  • Coma
  • Brain herniation and death 1, 2
  • Cardiorespiratory distress 2

Chronic Complications

• Mild to moderate symptoms:
  • Nausea and vomiting
  • Headache
  • Weakness
  • Cognitive impairment
  • Gait disturbances
  • Increased risk of falls and fractures 2
  • Osteoporosis 2
  • Attention deficits 3

Risk of Osmotic Demyelination Syndrome (ODS)

• Occurs with overly rapid correction of chronic hyponatremia
• Symptoms include dysarthria, dysphagia, altered mental status, and quadriparesis 1
• Risk factors: alcoholism, malnutrition, liver disease, and hypokalemia 1

Diagnostic Approach

Classification by Volume Status

1. Hypovolemic hyponatremia

   • Urine sodium: <20 mEq/L
   • Causes: Volume depletion, gastrointestinal losses, burns 1

2. Euvolemic hyponatremia

   • Urine osmolality: >500 mOsm/kg
   • Urine sodium: >20-40 mEq/L
   • Common cause: SIADH 1

3. Hypervolemic hyponatremia

   • Urine sodium: <20 mEq/L
   • Causes: Heart failure, cirrhosis, renal disease 1

Classification by Severity

• Mild: 130-134 mmol/L
• Moderate: 125-129 mmol/L
• Severe: <125 mmol/L 1

Classification by Chronicity

• Acute: <48 hours
• Chronic: >48 hours 1

Treatment Algorithm

1. Severe Symptomatic Hyponatremia (Medical Emergency)

• Administer 3% hypertonic saline:
  • 100-150 mL bolus or continuous infusion
  • Target correction: 4-6 mEq/L in first 6 hours or until symptoms improve
  • Maximum correction: 8 mEq/L in 24 hours, not exceeding 12 mEq/L in 24 hours 1, 2
  • Monitor serum sodium every 2-4 hours during active correction 1

2. Hypovolemic Hyponatremia

• Isotonic (0.9%) saline for plasma volume expansion
• Discontinue diuretics or other causative medications
• Reassess sodium levels after volume status correction 1

3. Euvolemic Hyponatremia (including SIADH)

• Fluid restriction (1-1.5 L/day)
• High solute intake (salt and protein)
• Consider oral sodium chloride tablets if no response to fluid restriction
• For refractory cases:
  • Tolvaptan (vasopressin receptor antagonist): starting at 15 mg once daily, can be titrated up to 60 mg daily 1, 4
  • Oral urea (30-60 g/day) as an alternative 1

4. Hypervolemic Hyponatremia

• Fluid restriction to 1,000 mL/day for moderate hyponatremia (120-125 mEq/L)
• More severe fluid restriction with albumin infusion for severe hyponatremia (<120 mEq/L)
• Treat underlying condition (heart failure, cirrhosis)
• Consider loop diuretics for volume management 1

Important Considerations and Pitfalls

Correction Rates

• Chronic hyponatremia: Maximum 8 mEq/L in 24 hours
• Acute hyponatremia: 1 mEq/L/hour
• High-risk patients (alcoholism, malnutrition, liver disease): Lower correction rate of 4-6 mEq/L per day 1

Medication Management

• Discontinue medications that may cause or worsen hyponatremia:
  • SSRIs
  • Carbamazepine
  • Thiazide diuretics
  • NSAIDs 1

Tolvaptan Considerations

• Effective for euvolemic and hypervolemic hyponatremia 4
• Short-term use recommended
• Side effects include thirst (12%), dry mouth (7%), polyuria (4%) 4
• Contraindicated with strong CYP3A inhibitors 4
• Risk of hypernatremia (1.7% vs 0.8% with placebo) 4
• Gastrointestinal bleeding risk in cirrhotic patients (10% vs 2% with placebo) 4

Prevention of Osmotic Demyelination Syndrome

• Avoid correction exceeding 8 mEq/L in 24 hours
• Consider administration of hypotonic fluids or desmopressin to prevent ODS if correction exceeds recommended rates 1
• Monitor serum sodium closely during active correction 1

By following this structured approach to diagnosis and management, the dangers of hyponatremia can be effectively addressed while minimizing the risk of treatment complications.