How do you manage a patient with hyponatremia?

Management of Hyponatremia

The management of hyponatremia 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

Initial Assessment and Classification

Severity Classification

• Mild hyponatremia: 130-135 mmol/L 2
• Moderate hyponatremia: 125-129 mmol/L 2
• Severe hyponatremia: <125 mmol/L 2

Even mild hyponatremia (130-135 mmol/L) should not be dismissed as clinically insignificant—it increases fall risk (21% vs. 5% in normonatremic patients), causes cognitive impairment, and carries a 60-fold increased mortality risk when sodium drops below 130 mmol/L (11.2% vs. 0.19%) 1, 3, 4

Essential Diagnostic Workup

When serum sodium is <135 mmol/L, obtain 1:

• Serum and urine osmolality
• Urine sodium concentration
• Urine electrolytes
• Serum uric acid (levels <4 mg/dL suggest SIADH with 73-100% positive predictive value) 1
• Assessment of extracellular fluid volume status

Critical distinction: In neurosurgical patients, you must differentiate SIADH from cerebral salt wasting (CSW), as they require opposite treatments—SIADH needs fluid restriction while CSW requires volume and sodium replacement 1

Emergency Management: Severe Symptomatic Hyponatremia

For patients with severe symptoms (seizures, coma, altered mental status, confusion, respiratory distress), immediately administer 3% hypertonic saline regardless of the underlying cause. 1, 2

Hypertonic Saline Protocol

• Initial goal: Correct by 6 mmol/L over the first 6 hours OR until severe symptoms resolve 1
• 24-hour limit: Total correction must NOT exceed 8 mmol/L in 24 hours 1, 2
• Administration: Give 100 mL of 3% saline over 10 minutes, can repeat up to 3 times at 10-minute intervals until symptoms improve 1
• Monitoring: Check serum sodium every 2 hours during initial correction 1

Critical pitfall: If you correct 6 mmol/L in the first 6 hours, you can only correct an additional 2 mmol/L in the remaining 18 hours to stay within the 8 mmol/L/24-hour limit 1

Management Based on Volume Status

Hypovolemic Hyponatremia

Characterized by: Orthostatic hypotension, dry mucous membranes, decreased skin turgor, urine sodium <30 mmol/L 1

Treatment approach:

• Discontinue diuretics immediately 1
• Administer isotonic saline (0.9% NaCl) for volume repletion 1, 2
• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
• Urine sodium <30 mmol/L predicts 71-100% response to saline 1

Euvolemic Hyponatremia (SIADH)

Characterized by: Normal volume status, urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg 1

Treatment hierarchy:

1. First-line: Fluid restriction to 1 L/day 1, 2
2. If no response: Add oral sodium chloride 100 mEq three times daily 1
3. Pharmacological options for resistant cases:
   • Tolvaptan 15 mg once daily, titrate to 30-60 mg 1, 5
   • Urea (40 g in 100-150 mL normal saline every 8 hours) 1
   • Demeclocycline or lithium (less commonly used due to side effects) 1

Important: Patients should be hospitalized for tolvaptan initiation to monitor for overly rapid correction 5. Do not use tolvaptan for more than 30 days due to liver injury risk 5

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Characterized by: Peripheral edema, ascites, jugular venous distention 1

Treatment approach:

• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 2
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• For cirrhotic patients: Consider albumin infusion (8 g/L of ascites removed) alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present—it worsens ascites and edema 1

Key concept: In cirrhosis, it is sodium restriction (not fluid restriction) that results in weight loss, as fluid passively follows sodium 1

Critical Correction Rate Guidelines

Standard Correction Rates

• Average risk patients: 4-8 mmol/L per day, maximum 10-12 mmol/L in 24 hours 1
• High-risk patients: 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1

High-Risk Populations Requiring Slower Correction

Patients with advanced liver disease, alcoholism, malnutrition, severe hyponatremia, hypophosphatemia, hypokalemia, or prior encephalopathy require the slower 4-6 mmol/L/day rate due to increased risk of osmotic demyelination syndrome 1, 6

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, this is a medical emergency requiring immediate intervention: 1, 6

1. Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1, 6
2. Consider desmopressin to slow or reverse the rapid rise 1, 6
3. Target relowering: Bring total 24-hour correction to ≤8 mmol/L from starting point 1, 6
4. Monitor for osmotic demyelination syndrome: Watch for dysarthria, dysphagia, oculomotor dysfunction, quadriparesis (typically appears 2-7 days after overcorrection) 1, 6

Special Populations

Neurosurgical Patients: SIADH vs. Cerebral Salt Wasting

This distinction is critical because treatments are opposite: 1

SIADH characteristics:

• Euvolemic state
• Urine sodium >20-40 mmol/L
• Treatment: Fluid restriction to 1 L/day 1

Cerebral Salt Wasting characteristics:

• True hypovolemia (CVP <6 cm H₂O)
• Urine sodium >20 mmol/L despite volume depletion
• Evidence of volume depletion (hypotension, tachycardia, dry mucous membranes) 1
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline 1
• For severe symptoms: 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily 1

Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm—this worsens outcomes 1

Cirrhotic Patients

• Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Require more cautious correction: 4-6 mmol/L per day maximum 1
• Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs. 2% placebo) 1, 5
• Only 1.2% of cirrhotic patients with ascites have sodium ≤120 mmol/L, demonstrating that severe hyponatremia is rare in this population 1

Common Pitfalls to Avoid

1. Overly rapid correction exceeding 8 mmol/L in 24 hours leads to osmotic demyelination syndrome 1
2. Inadequate monitoring during active correction 1
3. Using fluid restriction in cerebral salt wasting worsens outcomes 1
4. Failing to recognize and treat the underlying cause 1
5. Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
6. Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant 1, 3
7. Stopping diuretics prematurely in volume-overloaded heart failure patients due to mild hyponatremia 1

Monitoring Protocol

During Active Correction

• Severe symptoms: Check sodium every 2 hours 1
• Mild symptoms: Check sodium every 4 hours initially, then daily 1
• After symptom resolution: Continue monitoring every 4-6 hours for first 24 hours 1
• Track daily weights and fluid balance meticulously 1