What treatment should be given to a patient with mild to moderate hyponatremia?

Treatment of Mild to Moderate Hyponatremia

For mild to moderate hyponatremia, treatment depends primarily on volume status: fluid restriction to 1000 mL/day for euvolemic or hypervolemic patients, and isotonic saline for hypovolemic patients, with correction rates not exceeding 8 mmol/L in 24 hours. 1

Initial Assessment and Classification

Before initiating treatment, determine three critical factors:

• Volume status: Assess whether the patient is hypovolemic (dehydrated, hypotensive), euvolemic (normal volume), or hypervolemic (edema, ascites) 1
• Severity: Mild hyponatremia is defined as sodium 126-135 mEq/L, moderate as 120-125 mEq/L 2
• Symptom presence: Even mild hyponatremia can cause muscle cramps, nausea, weakness, headache, and gait instability 2

Check urine sodium and osmolality to help distinguish the underlying cause—urine sodium <30 mmol/L suggests hypovolemia (responds to saline), while >20 mEq/L with high urine osmolality suggests SIADH (requires fluid restriction) 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) to restore intravascular volume. 1, 2

• Continue isotonic fluids until euvolemia is achieved 1
• Monitor sodium levels to ensure correction does not exceed 8 mmol/L in 24 hours 1
• Once euvolemic, reassess if further sodium correction is needed 1

Euvolemic Hyponatremia (SIADH)

Implement fluid restriction to 1000 mL/day as first-line treatment. 1, 2

• Avoid fluid restriction during the first 24 hours if using pharmacologic therapy to prevent overly rapid correction 3
• If fluid restriction fails after several days, consider second-line options: oral urea or tolvaptan 15 mg once daily 1, 4
• Nearly half of SIADH patients do not respond to fluid restriction alone 4
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1000-1500 mL/day for sodium <125 mmol/L. 1, 2

• Discontinue or temporarily hold diuretics if sodium drops below 125 mmol/L 1
• In cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1
• Sodium restriction (2000-2500 mg/day) is more effective than fluid restriction for weight loss in cirrhosis, as fluid follows sodium 1

Correction Rate Guidelines

The maximum correction rate should not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1, 2, 4

• For patients with liver disease, alcoholism, or malnutrition, use even more conservative rates of 4-6 mmol/L per day due to higher risk of osmotic demyelination 1, 2
• Monitor sodium levels daily until stable 2
• For severe symptoms requiring hypertonic saline, aim for 6 mmol/L correction over 6 hours or until symptoms resolve, but still respect the 8 mmol/L per 24-hour limit 1

Pharmacologic Options for Refractory Cases

If fluid restriction fails in euvolemic or hypervolemic hyponatremia:

• Tolvaptan: Start at 15 mg once daily, can titrate to 30 mg then 60 mg at 24-hour intervals 3

  • Causes statistically greater increase in serum sodium compared to placebo (4.6 mEq/L greater increase at 30 days) 3
  • Effective across all disease etiologies including heart failure, cirrhosis, and SIADH 3
  • Use with caution in cirrhosis due to higher risk of gastrointestinal bleeding (10% vs 2% placebo) 1

• Oral urea: Considered very effective and safe, particularly for SIADH 4

Common Pitfalls to Avoid

• Do not ignore mild hyponatremia (130-135 mmol/L) as it increases fall risk (21% vs 5% in normonatremic patients) and mortality 1, 2
• Do not use hypertonic saline for mild-moderate asymptomatic hyponatremia—reserve this only for severe symptoms (seizures, altered mental status) 2, 5
• Do not use fluid restriction in cerebral salt wasting (common in neurosurgical patients)—this requires volume and sodium replacement instead 1
• Avoid overly rapid correction even in symptomatic patients, as osmotic demyelination syndrome can occur 2-7 days after rapid correction 1

Monitoring Requirements

• Check sodium levels every 4 hours initially during active correction 1
• Once stable, monitor daily until target reached 2
• Watch for signs of osmotic demyelination syndrome: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1
• If overcorrection occurs (>8 mmol/L in 24 hours), immediately switch to D5W and consider desmopressin to relower sodium 1