How to correct euvolemic hyponatremia?

Management of Euvolemic Hyponatremia

Primary Treatment Approach

Fluid restriction to 1 L/day is the cornerstone of treatment for euvolemic hyponatremia (SIADH), with oral sodium chloride supplementation (100 mEq three times daily) added if fluid restriction alone fails to improve sodium levels. 1

Initial Assessment

• Confirm euvolemia by examining for absence of orthostatic hypotension, dry mucous membranes, peripheral edema, ascites, or jugular venous distention 1
• Obtain urine sodium (typically >20-40 mmol/L in SIADH) and urine osmolality (typically >300 mOsm/kg) to support the diagnosis 1
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1
• Rule out hypothyroidism with TSH and assess adrenal function, as these must be normal for SIADH diagnosis 1

Treatment Algorithm Based on Symptom Severity

Asymptomatic or Mild Symptoms (Nausea, Headache, Weakness)

Step 1: Implement fluid restriction

• Restrict fluids to <1 L/day as first-line therapy 1, 2
• Avoid fluid restriction during the first 24 hours if initiating pharmacologic therapy to prevent overly rapid correction 3
• Patients can continue fluid intake in response to thirst when on vaptans 3

Step 2: Add oral sodium supplementation if no response

• Sodium chloride tablets 100 mEq orally three times daily 1
• Monitor serum sodium every 24 hours initially 1

Step 3: Consider pharmacologic agents for resistant cases

• Tolvaptan (vasopressin V2-receptor antagonist): Start 15 mg once daily, titrate to 30 mg then 60 mg at 24-hour intervals as needed 3
• Alternative agents: urea, demeclocycline, lithium, or loop diuretics 1, 4
• Tolvaptan increases serum sodium significantly more than placebo, with effects seen as early as 8 hours 3

Severe Symptoms (Seizures, Coma, Altered Mental Status)

Administer 3% hypertonic saline immediately with target correction of 6 mmol/L over 6 hours or until severe symptoms resolve 1, 2, 5

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals 1
• Monitor serum sodium every 2 hours during initial correction 1
• Switch to fluid restriction once symptoms resolve 1

Critical Correction Rate Guidelines

Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 3, 2

• Standard rate: 4-8 mmol/L per day 1
• High-risk patients (advanced liver disease, alcoholism, malnutrition, severe hyponatremia): limit to 4-6 mmol/L per day 1, 3
• If overcorrection occurs, immediately switch to D5W and consider desmopressin to relower sodium 1

Special Considerations

Distinguishing SIADH from Cerebral Salt Wasting (CSW)

This distinction is critical in neurosurgical patients as treatments are opposite 1:

SIADH characteristics:

• Euvolemic state with normal to slightly elevated CVP 1
• Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg 1
• Treatment: fluid restriction 1

CSW characteristics:

• True hypovolemia with CVP <6 cm H₂O 1
• Urine sodium >20 mmol/L despite volume depletion 1
• Treatment: volume and sodium replacement with isotonic/hypertonic saline, NOT fluid restriction 1
• Consider fludrocortisone 0.1-0.2 mg daily for severe cases 1

Tolvaptan-Specific Guidance

• Must initiate and re-initiate in hospital setting with close serum sodium monitoring 3
• Avoid fluid restriction during first 24 hours of tolvaptan therapy 3
• Do not use for more than 30 days to minimize liver injury risk 3
• Contraindicated with strong CYP3A inhibitors 3
• In clinical trials, 7% of patients with sodium <130 mEq/L had increases >8 mEq/L at 8 hours 3

Common Pitfalls to Avoid

• Using fluid restriction in CSW worsens outcomes - always distinguish from SIADH first 1
• Ignoring mild hyponatremia (130-135 mmol/L) increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1
• Inadequate monitoring during active correction leads to osmotic demyelination syndrome 1
• Failing to identify and treat underlying cause (malignancy, CNS disorders, pulmonary disease, medications) 1, 6
• Administering normal saline to euvolemic patients - this is only appropriate for hypovolemic hyponatremia 1

Monitoring Protocol

• Severe symptoms: Check sodium every 2 hours initially 1
• Mild symptoms: Check sodium every 4 hours after symptom resolution, then daily 1
• After discontinuation, resume fluid restriction and monitor for sodium changes 3
• Watch for osmotic demyelination syndrome signs (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically 2-7 days post-correction 1