What is the management of hyponatremia?

Management of Hyponatremia

Initial Assessment and Classification

Hyponatremia (serum sodium <135 mEq/L) requires systematic evaluation based on symptom severity, volume status, and correction rate limits to prevent both inadequate treatment and osmotic demyelination syndrome. 1

Start by determining:

• Severity: Mild (130-135 mEq/L), moderate (125-129 mEq/L), or severe (<125 mEq/L) 2
• Symptom severity: Asymptomatic, mild symptoms (nausea, weakness, headache), or severe symptoms (seizures, altered mental status, coma) 3, 2
• Acuity: Acute (<48 hours) vs chronic (>48 hours) - this determines safe correction rates 1
• Volume status: Hypovolemic, euvolemic, or hypervolemic 1, 4

Obtain serum and urine osmolality, urine sodium, and assess extracellular fluid volume status through physical examination (orthostatic hypotension, dry mucous membranes for hypovolemia; edema, ascites, JVD for hypervolemia) 1, 5

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, altered mental status, or cardiorespiratory distress, immediately administer 3% hypertonic saline with a target correction of 6 mEq/L over 6 hours or until symptoms resolve. 1, 3

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals 1
• Critical safety limit: Total correction must not exceed 8 mEq/L in 24 hours to prevent osmotic demyelination syndrome 1, 3
• Monitor serum sodium every 2 hours during initial correction 1
• If 6 mEq/L corrected in first 6 hours, only 2 mEq/L additional correction allowed in next 18 hours 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status:

Hypovolemic Hyponatremia:

• Discontinue diuretics immediately if sodium <125 mEq/L 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 mEq/L predicts good response to saline (71-100% positive predictive value) 1

Euvolemic Hyponatremia (SIADH):

• Fluid restriction to 1 L/day is the cornerstone of treatment 1, 2
• If no response, add oral sodium chloride 100 mEq three times daily 1
• For resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 6
• Alternative options: urea, demeclocycline, lithium, or loop diuretics 7, 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis):

• Implement fluid restriction to 1-1.5 L/day for sodium <125 mEq/L 1, 2
• Discontinue diuretics temporarily if sodium <125 mEq/L 1
• For cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present - it worsens edema and ascites 1
• Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to higher risk of GI bleeding (10% vs 2% placebo) 1, 6

Critical Correction Rate Guidelines

The single most important safety principle: Never exceed 8 mEq/L correction in 24 hours for chronic hyponatremia. 1, 3

Standard correction rates:

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

If overcorrection occurs:

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin to slow or reverse the rapid rise 1

Special Populations and Considerations

Neurosurgical Patients

Distinguish between SIADH and cerebral salt wasting (CSW) - they require opposite treatments. 7, 1

SIADH characteristics:

• Euvolemic state
• Urine sodium >20-40 mEq/L
• Urine osmolality >300 mOsm/kg
• Treatment: Fluid restriction 7, 1

Cerebral Salt Wasting characteristics:

• True hypovolemia (low CVP <6 cm H₂O)
• Urine sodium >20 mEq/L despite volume depletion
• Evidence of extracellular volume depletion
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 7, 1

For subarachnoid hemorrhage patients at risk of vasospasm:

• Never use fluid restriction - it worsens outcomes 7, 1
• Consider fludrocortisone (0.1-0.2 mg daily) to prevent vasospasm 7, 1
• Hydrocortisone may prevent natriuresis 7, 1

Cirrhotic Patients

• Hyponatremia in cirrhosis 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 rates (4-6 mEq/L per day) 1
• It is sodium restriction, not fluid restriction, that results in weight loss as fluid passively follows sodium 1
• Albumin infusion may be beneficial alongside fluid restriction 1

Common Pitfalls to Avoid

• Overly rapid correction exceeding 8 mEq/L in 24 hours causes osmotic demyelination syndrome - a devastating neurological complication that can result in parkinsonism, quadriparesis, or death 1, 3
• Using fluid restriction in cerebral salt wasting worsens outcomes 7, 1
• Inadequate monitoring during active correction 1
• Failing to recognize and treat the underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Ignoring mild hyponatremia (130-135 mEq/L) - even mild hyponatremia increases fall risk (21% vs 5%), fracture risk, and mortality (60-fold increase with sodium <130 mEq/L) 1, 3

Monitoring Requirements

• Severe symptoms: Check serum sodium every 2 hours during initial correction 1
• Mild symptoms: Check every 4 hours after symptom resolution 1
• Chronic management: Daily monitoring until stable, then every 24-48 hours 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1