What is the approach to managing a patient with hyponatremia?

Approach to Managing Hyponatremia

The management of hyponatremia requires immediate assessment of symptom severity and volume status, with correction rates never exceeding 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome, while addressing the underlying cause. 1

Initial Assessment and Classification

Determine symptom severity first, as this dictates urgency of treatment 1:

• Severe symptoms (seizures, coma, altered mental status, respiratory distress) constitute a medical emergency requiring immediate hypertonic saline 1, 2
• Mild-moderate symptoms include nausea, vomiting, headache, weakness, gait instability 2
• Asymptomatic or mild cases allow time for thorough diagnostic workup 1

Assess volume status through physical examination 1:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Euvolemic: no edema, normal blood pressure, moist mucous membranes 1
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1

Obtain essential laboratory tests 1:

• Serum and urine osmolality
• Urine sodium concentration
• Serum uric acid (< 4 mg/dL suggests SIADH with 73-100% positive predictive value) 1
• Thyroid function (TSH) and cortisol to exclude endocrine causes 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Emergency)

Administer 3% hypertonic saline immediately 1:

• Target: correct by 6 mmol/L over first 6 hours OR until severe symptoms resolve 1
• Maximum limit: total correction must not exceed 8 mmol/L in 24 hours 1
• Bolus dosing: 100 mL of 3% saline over 10 minutes, can repeat up to 3 times at 10-minute intervals 1
• Monitor sodium every 2 hours during initial correction 1

Chronic or Asymptomatic Hyponatremia

Treatment depends on volume status:

Hypovolemic Hyponatremia 1:

• Discontinue diuretics immediately 1
• Administer isotonic saline (0.9% NaCl) for volume repletion 1
• Urine sodium < 30 mmol/L predicts good response to saline (71-100% positive predictive value) 1

Euvolemic Hyponatremia (SIADH) 1:

• First-line: Fluid restriction to 1 L/day 1
• If no response: Add oral sodium chloride 100 mEq three times daily 1
• Pharmacologic options: Vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 3
• Alternative agents: urea, demeclocycline, lithium (less commonly used) 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis) 1:

• Fluid restriction to 1-1.5 L/day for sodium < 125 mmol/L 1
• Discontinue diuretics temporarily if sodium < 125 mmol/L 1
• For cirrhosis: Consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present (worsens ascites/edema) 1

Critical Correction Rate Guidelines

Standard correction rates 1:

• Average risk patients: 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours 1
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1

If overcorrection occurs 1:

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin to slow or reverse rapid rise 1
• Goal: bring total 24-hour correction to no more than 8 mmol/L from starting point 1

Special Populations and Considerations

Neurosurgical patients require distinction between SIADH and cerebral salt wasting (CSW) 1:

• SIADH: euvolemic, treat with fluid restriction 1
• CSW: hypovolemic (CVP < 6 cm H₂O), treat with volume and sodium replacement, NOT fluid restriction 1
• Subarachnoid hemorrhage patients at risk of vasospasm: never use fluid restriction 1
• Consider fludrocortisone 0.1-0.2 mg daily for CSW or to prevent vasospasm 1

Cirrhotic patients 1:

• 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) 1
• Tolvaptan carries higher risk of gastrointestinal bleeding (10% vs 2% placebo) 3

Common Pitfalls to Avoid

Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours - this causes osmotic demyelination syndrome with devastating neurological consequences (dysarthria, dysphagia, quadriparesis, death) 1

Do not use fluid restriction in cerebral salt wasting - this worsens outcomes 1

Do not ignore mild hyponatremia (130-135 mmol/L) - even mild chronic hyponatremia increases fall risk (21% vs 5%), mortality (60-fold increase), and cognitive impairment 1, 2, 4

Inadequate monitoring during active correction leads to overcorrection 1

Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms worsens fluid overload 1

Failing to identify and treat the underlying cause leads to recurrence 1

Monitoring Requirements

• Severe symptoms: Check sodium every 2 hours during initial correction 1
• After symptom resolution: Check every 4 hours 1
• Chronic management: Daily sodium checks initially, then adjust based on response 1
• Watch for osmotic demyelination syndrome 2-7 days after rapid correction (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) 1