What is the appropriate management approach for a patient presenting with hyponatremia?

Management of Hyponatremia

Hyponatremia (serum sodium <135 mmol/L) requires immediate assessment of volume status, symptom severity, and chronicity to guide treatment, with the critical principle being that correction must never exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Initial Assessment and Classification

Determine three critical factors before initiating treatment:

• Symptom severity: Severe symptoms (seizures, coma, altered consciousness, respiratory distress) constitute a medical emergency requiring immediate hypertonic saline 1, 2
• Chronicity: Acute (<48 hours) vs. chronic (>48 hours) hyponatremia—acute can be corrected more rapidly without risk of osmotic demyelination, while chronic requires cautious correction 1, 3
• Volume status: Assess for hypovolemia (orthostatic hypotension, dry mucous membranes, decreased skin turgor), euvolemia (normal volume status), or hypervolemia (peripheral edema, ascites, jugular venous distention) 1, 4

Essential initial workup includes:

• Serum and urine osmolality, urine sodium, and uric acid 1
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1
• Urine sodium <30 mmol/L predicts 71-100% response to saline infusion in hypovolemic states 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, altered consciousness, or respiratory distress, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 5, 4

• Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1
• Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 6, 5
• Monitor serum sodium every 2 hours during initial correction 1
• Consider ICU admission for close monitoring 1

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status and underlying etiology 1, 4

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Administer isotonic saline (0.9% NaCl) for volume repletion:

• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
• Discontinue diuretics immediately if sodium <125 mmol/L 1, 7
• Urine sodium <30 mmol/L confirms hypovolemic state and predicts good response to saline 1
• Once euvolemic, reassess and adjust treatment based on sodium response 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH: 1, 5, 7

• If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• For persistent cases despite fluid restriction, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 6, 5
• Alternative pharmacological options include urea, demeclocycline, or lithium (less commonly used due to side effects) 1, 5, 8
• Tolvaptan requires hospital initiation and should not be used for more than 30 days due to liver injury risk 6

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L: 1, 4, 7

• Temporarily discontinue diuretics if sodium <125 mmol/L 1
• In cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1
• Treat underlying condition (optimize heart failure management, manage cirrhosis complications) 1, 7
• Vasopressin receptor antagonists 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

Critical Correction Rate Guidelines

The single most important safety principle is limiting correction rate to prevent osmotic demyelination syndrome:

• Standard patients: Maximum 8 mmol/L in 24 hours 1, 3, 5
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): Maximum 4-6 mmol/L per day 1, 3
• For severe symptoms, correct by 6 mmol/L in first 6 hours, then only 2 mmol/L additional in next 18 hours 1
• Never exceed 1 mmol/L/hour correction rate for chronic hyponatremia 1

Special Populations and Considerations

Neurosurgical Patients

Distinguish between SIADH and cerebral salt wasting (CSW), as they require opposite treatments: 1

• SIADH: Euvolemic, treat with fluid restriction 1
• CSW: Hypovolemic with high urine sodium despite volume depletion, treat with volume and sodium replacement (isotonic or hypertonic saline), never fluid restriction 1
• For severe CSW symptoms, administer 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily 1
• In subarachnoid hemorrhage patients at risk of vasospasm, never use fluid restriction—consider fludrocortisone or hydrocortisone to prevent natriuresis 1

Cirrhotic Patients

Hyponatremia in cirrhosis reflects worsening hemodynamic status and increases risk of complications: 1

• Serum sodium ≤130 mmol/L increases risk of hepatic encephalopathy (OR 2.36), hepatorenal syndrome (OR 3.45), and spontaneous bacterial peritonitis (OR 3.40) 1
• Require more cautious correction (4-6 mmol/L per day) due to higher risk of osmotic demyelination 1
• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Note: It is sodium restriction, not fluid restriction, that results in weight loss as fluid passively follows sodium 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediate intervention is required: 1, 3

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin to slow or reverse the rapid rise in serum sodium 1, 3
• Monitor for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Common Pitfalls to Avoid

• Overly rapid correction exceeding 8 mmol/L in 24 hours leading to osmotic demyelination syndrome 1, 5
• Inadequate monitoring during active correction—check sodium every 2 hours for severe symptoms, every 4 hours for mild symptoms 1
• Using fluid restriction in cerebral salt wasting, which worsens outcomes 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 mmol/L) as clinically insignificant—even mild hyponatremia increases fall risk (21% vs. 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1, 2, 5

Monitoring Requirements

• Severe symptoms: Monitor serum sodium every 2 hours during initial correction 1
• After resolution of severe symptoms: Monitor every 4 hours 1
• Mild symptoms or asymptomatic: Monitor every 24-48 hours initially 1
• Track daily weight, fluid balance, and clinical volume status 1
• Watch for signs of osmotic demyelination syndrome 2-7 days post-correction 1