What is the treatment approach for a patient with hyponatremia?

Treatment of Hyponatremia

Hyponatremia treatment depends critically on three factors: symptom severity, volume status (hypovolemic, euvolemic, or hypervolemic), and chronicity (acute <48 hours vs. chronic >48 hours), with the overriding principle being that correction must never exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Immediate Assessment

Before initiating treatment, rapidly determine:

• Symptom severity: Severe symptoms (seizures, coma, altered mental status) require immediate hypertonic saline; mild symptoms (nausea, headache, weakness) allow slower correction 1, 2
• Volume status: Check for orthostatic hypotension, dry mucous membranes, skin turgor (hypovolemic); peripheral edema, ascites, jugular venous distention (hypervolemic); or absence of both (euvolemic) 1, 3
• Serum and urine osmolality: Confirm true hypotonic hyponatremia (serum osmolality <275 mOsm/kg) 1, 4
• Urine sodium: <30 mmol/L suggests hypovolemia responsive to saline; >20-40 mmol/L with high urine osmolality suggests SIADH 1, 5

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, confusion, or altered consciousness, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over the first 6 hours or until symptoms resolve. 1, 5, 6

• Initial bolus approach: Give 100 mL of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1
• Continuous infusion calculation: Initial rate (mL/kg/hour) = body weight (kg) × desired sodium increase (mmol/L/hour) 1, 7
• Maximum correction limit: Never exceed 8 mmol/L total correction in 24 hours, even if symptoms persist 1, 5, 4
• Monitoring frequency: Check serum sodium every 2 hours during active correction 1, 3
• ICU admission required for continuous monitoring and rapid intervention capability 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment is determined by volume status rather than immediate hypertonic saline 1, 3, 6

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Administer isotonic saline (0.9% NaCl) for volume repletion, as the primary problem is sodium and water depletion. 1, 3, 6

• Initial infusion rate: 15-20 mL/kg/hour initially, then 4-14 mL/kg/hour based on clinical response 1
• Discontinue diuretics immediately if sodium <125 mmol/L 1, 4
• Urine sodium <30 mmol/L predicts good response to saline with 71-100% positive predictive value 1
• Monitor for euvolemia: Normal blood pressure, moist mucous membranes, stable vital signs 1
• Once euvolemic, switch to maintenance isotonic fluids at 30 mL/kg/day 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 3, 5

• First-line: Restrict fluids to <1000 mL/day 1, 6
• If no response after 48-72 hours: Add oral sodium chloride 100 mEq (approximately 6 grams) three times daily 1
• Pharmacological options for refractory cases:
  • Urea 15-30 grams twice daily (effective but poor palatability) 1, 5
  • Tolvaptan 15 mg once daily, titrate to 30-60 mg (vasopressin receptor antagonist) 1, 8, 5
  • Demeclocycline 300-600 mg twice daily (less commonly used due to side effects) 1, 9
• Monitor sodium every 24 hours initially to ensure correction stays within safe limits 1, 3

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L, as the primary problem is excess total body water despite increased total body sodium. 1, 3, 4

• Fluid restriction: 1000-1500 mL/day is first-line therapy 1, 4
• Temporarily discontinue diuretics if sodium <125 mmol/L until sodium improves 1, 4
• For cirrhotic patients: Consider albumin infusion (6-8 grams per liter of ascites drained) alongside fluid restriction 1, 4
• Sodium restriction: 2-2.5 g/day (88-110 mmol/day) is more important than fluid restriction for weight loss, as fluid follows sodium 1, 4
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1, 4
• Vaptans (tolvaptan): Consider only for persistent severe hyponatremia despite fluid restriction and maximized guideline-directed therapy; use with extreme caution in cirrhosis due to 10% gastrointestinal bleeding risk vs. 2% with placebo 1, 8

Critical Correction Rate Guidelines

The single most important safety principle is never exceeding 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome. 1, 3, 5

Standard Correction Rates

• Average-risk patients: 4-8 mmol/L per day, maximum 10-12 mmol/L in 24 hours 1
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy, severe hyponatremia <120 mmol/L): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 3, 4
• Acute hyponatremia (<48 hours): Can be corrected more rapidly without osmotic demyelination risk 1
• Chronic hyponatremia (>48 hours): Requires slower, cautious correction 1, 3

Managing Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately intervene to prevent osmotic demyelination syndrome. 1

• Discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Administer desmopressin to slow or reverse the rapid sodium rise 1
• Target relowering: Bring total 24-hour correction to no more than 8 mmol/L from starting point 1
• Watch for osmotic demyelination signs: Dysarthria, dysphagia, oculomotor dysfunction, quadriparesis typically appearing 2-7 days after rapid correction 1, 3

Special Populations and Considerations

Neurosurgical Patients (Cerebral Salt Wasting vs. SIADH)

In neurosurgical patients, distinguishing cerebral salt wasting (CSW) from SIADH is critical because they require opposite treatments. 1, 3

• SIADH characteristics: Euvolemic, urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg; treat with fluid restriction 1
• CSW characteristics: True hypovolemia (CVP <6 cm H₂O), urine sodium >20 mmol/L despite volume depletion, orthostatic hypotension; treat with volume and sodium replacement 1
• CSW treatment: Normal saline 50-100 mL/kg/day or 3% hypertonic saline for severe cases, plus fludrocortisone 0.1-0.2 mg daily 1, 3
• Never use fluid restriction in CSW as this worsens outcomes 1, 3
• Subarachnoid hemorrhage patients at risk for vasospasm: Avoid fluid restriction; consider fludrocortisone or hydrocortisone to prevent natriuresis 1, 3

Cirrhotic Patients

Cirrhotic patients require even more cautious correction (4-6 mmol/L per day maximum) due to higher risk of osmotic demyelination syndrome. 1, 4

• Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1, 4
• Chronic hyponatremia is common: Only 1.2% of cirrhotic patients with ascites have sodium ≤120 mmol/L 1
• Fluid restriction rarely improves sodium significantly but prevents further decline 1, 4
• Reserve hypertonic saline for life-threatening symptoms or imminent liver transplantation 1

Common Pitfalls to Avoid

• Never ignore mild hyponatremia (130-135 mmol/L): Associated with 60-fold increased mortality risk, increased falls (21% vs. 5%), and cognitive impairment 1, 2, 5
• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours: Causes osmotic demyelination syndrome 1, 3, 5
• Never use fluid restriction in cerebral salt wasting: Worsens outcomes 1, 3
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms: Worsens edema and ascites 1, 4
• Never rely on physical examination alone for volume status: Sensitivity only 41.1%, specificity 80% 1
• Never fail to monitor sodium levels during active correction: Check every 2 hours for severe symptoms, every 4 hours for mild symptoms 1, 3
• Never use hypotonic fluids (lactated Ringer's, 0.45% saline) in hyponatremia: Worsens the condition 1, 6

Monitoring Protocol

• Severe symptoms: Check sodium every 2 hours during initial correction 1, 3
• Mild symptoms: Check sodium every 4 hours after symptom resolution 1
• Asymptomatic chronic hyponatremia: Check sodium every 24 hours initially, then adjust based on response 1, 3
• Daily weights and strict intake/output to assess volume status 1
• Watch for osmotic demyelination syndrome signs 2-7 days post-correction 1, 3