How do you treat hypo-osmolar hyponatremia?

Treatment of Hypo-osmolar Hyponatremia

Treatment of hypo-osmolar hyponatremia depends critically on three factors: volume status (hypovolemic, euvolemic, or hypervolemic), symptom severity, and chronicity, with correction rates never exceeding 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Initial Assessment

Before initiating treatment, determine the following:

• Volume status through physical examination: look for orthostatic hypotension, dry mucous membranes, and decreased skin turgor (hypovolemia) versus peripheral edema, ascites, and jugular venous distention (hypervolemia) 1
• Symptom severity: severe symptoms include seizures, coma, altered mental status, or respiratory distress requiring immediate intervention 2
• Chronicity: acute (<48 hours) versus chronic (>48 hours) hyponatremia, as chronic cases require slower correction 1
• Urine sodium and osmolality: urine sodium <30 mmol/L suggests hypovolemia; >20-40 mmol/L with urine osmolality >300 mOsm/kg suggests SIADH 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, or altered mental status, immediately administer 3% hypertonic saline regardless of sodium level. 2

• Goal: Correct 6 mmol/L over the first 6 hours or until symptoms resolve 1, 2
• Administration: Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals 1
• Maximum correction: Never exceed 8 mmol/L in 24 hours 1, 2
• Monitoring: Check serum sodium every 2 hours during initial correction 1, 2

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status:

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion. 1

• Indication: Urine sodium <30 mmol/L with clinical signs of volume depletion 1
• Monitoring: Check sodium every 4-6 hours 1
• Caution: Even isotonic saline can correct sodium too rapidly in severe hyponatremia; monitor closely 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 3

• First-line: Restrict fluids to <1 L/day 1, 4
• If inadequate response: Add oral sodium chloride 100 mEq three times daily 1
• Pharmacological options for resistant cases:
  • Tolvaptan 15 mg once daily, titrated to 30-60 mg as needed 5
  • Urea (though less palatable) 6
  • Demeclocycline or lithium (less commonly used due to side effects) 1
• Goal correction: 4-6 mmol/L per day 1

Important distinction: In neurosurgical patients, cerebral salt wasting (CSW) mimics SIADH but requires opposite treatment—volume and sodium replacement, NOT fluid restriction. 3 CSW is characterized by true hypovolemia with CVP <6 cm H₂O despite high urine sodium. 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L. 1

• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• For cirrhotic patients: Consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 1
• Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to higher risk of gastrointestinal bleeding (10% vs 2% placebo) 1, 5

Critical Correction Rate Guidelines

The maximum correction rate must never exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1, 6

Standard Patients

• Target: 4-8 mmol/L per day, not exceeding 10-12 mmol/L in 24 hours 1

High-Risk Patients

Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require even slower correction at 4-6 mmol/L per day. 1, 3

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours:

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider desmopressin to slow or reverse the rapid rise 1
• Monitor closely for signs of osmotic demyelination syndrome: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis (typically occurring 2-7 days after rapid correction) 1

Special Populations

Neurosurgical Patients

• Distinguish SIADH from cerebral salt wasting: CSW requires volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 3
• Fludrocortisone may be considered in subarachnoid hemorrhage patients at risk for vasospasm 3
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 3

Cirrhotic Patients

• Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 7, 1
• Albumin infusion should be tried before tolvaptan 1
• Avoid rapid correction: Use conservative rates of 4-6 mmol/L per day 1

Common Pitfalls to Avoid

• Using normal saline in SIADH: This can paradoxically worsen hyponatremia due to high urine osmolality causing net free water retention 4
• Fluid restriction in cerebral salt wasting: This worsens outcomes; CSW requires volume replacement 1, 3
• Ignoring mild hyponatremia (130-135 mmol/L): Even mild hyponatremia increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1
• Overly rapid correction: Exceeding 8 mmol/L in 24 hours risks osmotic demyelination syndrome, which can cause irreversible neurological damage 1, 6
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms: This worsens fluid overload 1

Monitoring Requirements

• Severe symptoms: Check sodium every 2 hours during initial correction 1, 2
• After symptom resolution: Check every 4-6 hours 1
• Chronic hyponatremia: Monitor daily to ensure correction does not exceed 8 mmol/L in 24 hours 1