What is the protocol for managing hyponatremia?

Management Protocol for Hyponatremia

The management of hyponatremia should be based on volume status assessment, symptom severity, and rate of onset, with a maximum correction rate of 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Initial Assessment and Classification

• Hyponatremia is defined as serum sodium <135 mmol/L and classified as mild (126-135 mEq/L), moderate (120-125 mEq/L), or severe (<120 mEq/L) 1, 2
• Initial workup should include serum and urine osmolarity, urine electrolytes, uric acid, and assessment of extracellular fluid volume status to determine the underlying cause 1
• Classify patients according to volume status: hypovolemic, euvolemic, or hypervolemic 1, 3
• Serum uric acid <4 mg/dL has a positive predictive value of 73-100% for SIADH, though this may include patients with cerebral salt wasting (CSW) 1
• Urinary sodium <30 mmol/L has a positive predictive value of 71-100% for response to 0.9% saline infusion 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (seizures, coma)

• Administer 3% hypertonic saline with an initial goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve 1
• Consider ICU admission for close monitoring during treatment 1
• Monitor serum sodium every 2 hours during initial correction 1
• Do not exceed total correction of 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 4

Moderate or Asymptomatic Hyponatremia

• Treatment approach depends on volume status 1, 3
• Limit correction rate to <8 mmol/L per 24 hours, with even more cautious correction (4-6 mmol/L per day) for high-risk patients (advanced liver disease, alcoholism, malnutrition) 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

• Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion 1, 5
• For severe dehydration with neurological symptoms, consider hypertonic saline with careful monitoring 1

Euvolemic Hyponatremia (SIADH)

• Implement fluid restriction to 1L/day for mild/asymptomatic cases 1, 4
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction 1
• For severe symptomatic cases, use 3% hypertonic saline with careful monitoring 1
• Consider second-line therapies for resistant cases:
  • Urea (considered effective and safe) 1, 4
  • Tolvaptan (vasopressin receptor antagonist) starting at 15 mg once daily for resistant cases 1, 6
  • Other options include demeclocycline, lithium, or diuretics 1

Hypervolemic Hyponatremia (e.g., cirrhosis, heart failure)

• Implement fluid restriction to 1000-1500 mL/day for moderate hyponatremia (Na 120-125 mmol/L) 1, 5
• For severe hyponatremia (<120 mmol/L), implement more severe fluid restriction plus albumin infusion 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1

Special Considerations

Cerebral Salt Wasting (CSW)

• Treatment focuses on volume and sodium replacement, not fluid restriction 1
• For severe symptoms, administer 3% hypertonic saline and consider fludrocortisone 1
• Avoid fluid restriction in CSW as it can worsen outcomes 1

Patients with Liver Disease

• Use more cautious correction rates (4-6 mmol/L per day) due to higher risk of osmotic demyelination syndrome 1
• Consider albumin infusion alongside fluid restriction 1
• Hyponatremia in cirrhosis reflects worsening hemodynamic status and increases risk for hepatic encephalopathy, hepatorenal syndrome, and spontaneous bacterial peritonitis 1

Monitoring and Safety Considerations

• Calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1
• For severe symptoms: monitor serum sodium every 2 hours during initial correction 1
• For mild to moderate symptoms: monitor daily until stable 1, 2
• If overcorrection occurs, consider relowering with electrolyte-free water or desmopressin 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Common Pitfalls to Avoid

• Overly rapid correction of chronic hyponatremia leading to osmotic demyelination syndrome 1, 2
• Inadequate monitoring during active correction 1
• Using fluid restriction in CSW 1
• Failing to recognize and treat the underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1, 2
• Ignoring mild hyponatremia (135 mmol/L) as clinically insignificant 1

Pharmacological Interventions

• Tolvaptan has been shown effective for euvolemic or hypervolemic hyponatremia in clinical trials, with mean serum sodium increases of 4.0 mEq/L by day 4 and 6.2 mEq/L by day 30 6
• Common adverse effects of tolvaptan include thirst, dry mouth, and increased urination 6
• In patients with cirrhosis treated with tolvaptan, gastrointestinal bleeding was reported in 10% of patients (vs 2% with placebo) 6
• Hypernatremia can occur with tolvaptan treatment (1.7% vs 0.8% with placebo) 6