What is the approach to managing hyponatremia?

Management of Hyponatremia

The approach to managing hyponatremia should be based on volume status assessment, symptom severity, and correction rate control, with treatment tailored to the underlying cause while strictly limiting correction to prevent osmotic demyelination syndrome.

Initial Assessment and Classification

• Hyponatremia (serum sodium <135 mmol/L) should be evaluated based on volume status (hypovolemic, euvolemic, or hypervolemic) and serum osmolality to determine the underlying cause 1
• Initial workup should include serum and urine osmolarity, urine electrolytes, uric acid, and assessment of extracellular fluid volume status 1
• Urinary sodium <30 mmol/L has a positive predictive value of 71-100% for response to 0.9% saline infusion, while serum uric acid <4 mg/dL has a positive predictive value of 73-100% for SIADH 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, 2
• For patients with severe symptoms, monitor serum sodium every 2 hours during initial correction 1
• Calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1

Mild to Moderate Symptomatic Hyponatremia

• Correction rate should not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 3
• For chronic hyponatremia, avoid rapid correction exceeding 1 mmol/L/hour 1
• Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require more cautious correction (4-6 mmol/L per day) 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

• Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion 1, 4
• 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, 5
• For moderate cases (Na 120-125 mmol/L), fluid restriction to 1-1.5 L/day 1
• Consider additional options for resistant cases: urea, diuretics, lithium, demeclocycline 1
• For severe symptomatic cases, administer 3% hypertonic saline with careful monitoring 1
• Vasopressin receptor antagonists (tolvaptan) may be considered for clinically significant hyponatremia resistant to fluid restriction 1, 6

Hypervolemic Hyponatremia (cirrhosis, heart failure)

• Implement fluid restriction to 1000-1500 mL/day for serum sodium <125 mmol/L 1, 7
• Consider albumin infusion for patients with cirrhosis 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1
• Temporarily discontinue diuretics if sodium <125 mmol/L 1

Special Considerations

Cerebral Salt Wasting vs. SIADH

• In neurosurgical patients, cerebral salt wasting (CSW) is more common than SIADH 1
• CSW should be treated with replacement of serum sodium and intravenous fluids, not fluid restriction 1
• Fludrocortisone may be considered for hyponatremia in subarachnoid hemorrhage patients at risk of vasospasm 1
• Avoid fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1

Pharmacological Interventions

• Tolvaptan has been shown effective in treating euvolemic or hypervolemic hyponatremia in clinical trials, increasing serum sodium levels significantly more than placebo 6
• When using tolvaptan, monitor for overly rapid correction of sodium levels and potential drug interactions 6
• Tolvaptan should be used with caution in cirrhotic patients due to higher risk of gastrointestinal bleeding (10% vs 2% with placebo) 1

Common Pitfalls to Avoid

• Overly rapid correction of chronic hyponatremia leading to osmotic demyelination syndrome 1, 3
• Inadequate monitoring during active correction 1
• Using fluid restriction in CSW, which can worsen outcomes 1
• Failing to recognize and treat the underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Ignoring mild hyponatremia (135 mmol/L) as clinically insignificant 1

Monitoring and Follow-up

• For severe symptoms: monitor serum sodium every 2 hours during initial correction 1
• After resolution of severe symptoms, check sodium every 4 hours 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1
• If overcorrection occurs, consider relowering with electrolyte-free water or desmopressin 1