What is the recommended treatment for outpatient management of chronic hyponatremia?

Outpatient Management of Chronic Hyponatremia

For outpatient management of chronic hyponatremia, the cornerstone of treatment is fluid restriction to 1000 mL/day for euvolemic hyponatremia (SIADH), while hypervolemic hyponatremia requires fluid restriction to 1000-1500 mL/day combined with sodium restriction and discontinuation of contributing diuretics. 1

Initial Assessment and Classification

Before initiating treatment, determine the volume status and severity of hyponatremia:

• Obtain serum and urine osmolality, urine sodium, uric acid, and assess extracellular fluid volume status to establish the underlying cause 1
• Classify by severity: mild (130-135 mEq/L), moderate (120-125 mEq/L), or severe (<120 mEq/L) 1
• Assess volume status: Look for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemic); jugular venous distention, peripheral edema, ascites (hypervolemic); or absence of these findings (euvolemic) 1, 2
• Urine sodium <30 mmol/L suggests hypovolemic hyponatremia with 71-100% positive predictive value for response to saline 1
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1

Treatment Based on Volume Status

Euvolemic Hyponatremia (SIADH)

Fluid restriction is the cornerstone of treatment:

• Restrict fluids to 1000 mL/day (1 L/day) as first-line therapy 1, 2, 3
• If no response to fluid restriction after adequate trial, add oral sodium chloride 100 mEq three times daily 1
• Nearly half of SIADH patients do not respond to fluid restriction alone 3

Second-line pharmacological options when fluid restriction fails:

• Oral urea is considered very effective and safe - though it has poor palatability and may cause gastric intolerance 2, 3
• Tolvaptan 15 mg once daily can be considered for clinically significant hyponatremia resistant to fluid restriction 1, 4, 2
• Demeclocycline, lithium, or loop diuretics may be considered but are less commonly used 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Treatment focuses on fluid and sodium restriction:

• Implement fluid restriction to 1000-1500 mL/day for serum sodium <125 mEq/L 1, 3
• Recommend salt intake of 5-6.5 g/day (sodium 2-2.5 g/day, 88-110 mmol/day) 1
• Temporarily discontinue diuretics if sodium <125 mEq/L 1
• For cirrhotic patients, consider albumin infusion alongside fluid restriction 1, 3
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1

Note that it is sodium restriction, not fluid restriction, that results in weight loss as fluid passively follows sodium 1

Hypovolemic Hyponatremia

Volume repletion is the primary treatment:

• Discontinue diuretics immediately 1
• Administer isotonic saline (0.9% NaCl) for volume repletion 1, 5
• Once euvolemic, reassess and treat any underlying cause 1

Correction Rate Guidelines - Critical Safety Considerations

The maximum correction rate must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2, 3, 6

• For average-risk patients: aim for 4-8 mmol/L per day 1
• For high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): limit to 4-6 mmol/L per day 1, 2
• Chronic hyponatremia should not be corrected rapidly (>1 mmol/L/hour) 1

Monitoring Requirements

• For mild symptoms or asymptomatic patients: monitor serum sodium every 24 hours initially, then adjust frequency based on response 1
• Track daily weight and fluid balance 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Special Populations and Considerations

Cirrhotic Patients

• Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs 2% placebo) 1
• Use conservative correction rates (4-6 mmol/L per day) 1

Neurosurgical Patients

• Distinguish between SIADH and cerebral salt wasting (CSW) - treatment approaches differ fundamentally 1, 7
• CSW requires volume and sodium replacement, NOT fluid restriction 1, 7
• Fluid restriction in CSW worsens outcomes 1

Common Pitfalls to Avoid

• Never ignore mild hyponatremia (130-135 mmol/L) - it increases fall risk (21% vs 5% in normonatremic patients) and mortality (60-fold increase) 1, 2
• Never use fluid restriction in cerebral salt wasting 1
• Never exceed 8 mmol/L correction in 24 hours - overly rapid correction causes osmotic demyelination syndrome 1, 2, 3
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Never fail to discontinue contributing medications (diuretics, SSRIs, antidepressants) 1

When to Refer or Hospitalize

• Serum sodium <120 mEq/L requires immediate intervention and likely hospitalization 1, 6
• Any neurological symptoms (confusion, seizures, altered mental status) require emergency treatment with hypertonic saline 1, 2, 6
• Failure to respond to outpatient fluid restriction after adequate trial 3