What is the management approach for hyponatremia?

Hyponatremia Management

Initial Assessment and Classification

Hyponatremia (serum sodium <135 mmol/L) requires systematic evaluation based on volume status, symptom severity, and onset timing to guide appropriate treatment and prevent complications. 1

• Assess volume status clinically: look for orthostatic hypotension, dry mucous membranes, skin turgor (hypovolemic); jugular venous distention, peripheral edema, ascites (hypervolemic); or absence of these findings (euvolemic) 1
• Obtain serum and urine osmolality, urine sodium, and urine electrolytes to determine the underlying cause 1
• Classify severity: mild (126-135 mmol/L), moderate (120-125 mmol/L), or severe (<120 mmol/L) 1, 2
• Determine acuity: acute (<48 hours) versus chronic (>48 hours), as this critically impacts correction rates 1
• Check serum uric acid: <4 mg/dL suggests SIADH or cerebral salt wasting with 73-100% positive predictive value 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)

Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1
• Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 3
• 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 entirely on volume status:

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion. 1

• Urinary sodium <30 mmol/L has 71-100% positive predictive value for response to saline infusion 1
• Once euvolemic, reassess and adjust management based on sodium response 1
• Correct at maximum 8 mmol/L per 24 hours 1

Euvolemic Hyponatremia (SIADH)

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

• If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• For resistant cases, consider urea, demeclocycline, lithium, or loop diuretics 1
• Vasopressin receptor antagonists (tolvaptan 15 mg daily, titrate to 30-60 mg) may be used for persistent euvolemic hyponatremia 1, 4
• Avoid fluid restriction in neurosurgical patients with subarachnoid hemorrhage at risk for vasospasm 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1

• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• In cirrhotic patients, consider albumin infusion (6-8 g per liter of ascites drained) alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens edema and ascites 1
• Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction and maximized guideline-directed therapy, but use with extreme caution in cirrhosis due to 10% gastrointestinal bleeding risk versus 2% with placebo 1, 4
• Note: sodium restriction (not fluid restriction) produces weight loss, as fluid passively follows sodium 1

Correction Rate Guidelines

The maximum correction rate is 8 mmol/L in 24 hours for all patients. 1, 3

• For high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy, severe hyponatremia, hypokalemia, hypophosphatemia), limit correction to 4-6 mmol/L per day 1
• For chronic hyponatremia, avoid correction faster than 1 mmol/L per hour 1
• Calculate sodium deficit: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1

Special Considerations for Neurosurgical Patients

In neurosurgical patients, distinguish between SIADH and cerebral salt wasting (CSW), as treatment approaches are fundamentally opposite. 1

• CSW requires volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
• CSW is more common than SIADH in neurosurgical patients, particularly with subarachnoid hemorrhage, poor clinical grade, and hydrocephalus 1
• Evidence of volume depletion (hypotension, tachycardia, dry mucous membranes) with urinary sodium >20 mmol/L suggests CSW 1
• For severe CSW symptoms, administer 3% hypertonic saline plus fludrocortisone 1
• Consider hydrocortisone to prevent natriuresis in subarachnoid hemorrhage patients 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water). 1

• Administer desmopressin to slow or reverse the rapid rise in serum sodium 1
• Target reduction to bring total 24-hour correction to no more than 8 mmol/L from starting point 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Common Pitfalls to Avoid

• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant: even mild hyponatremia increases fall risk (21% vs 5% in normonatremic patients) and is associated with 60-fold increased mortality when <130 mmol/L 1
• Using fluid restriction in cerebral salt wasting worsens outcomes 1
• Administering hypertonic saline for hypervolemic hyponatremia without life-threatening symptoms worsens fluid overload 1
• Inadequate monitoring during active correction leads to overcorrection and osmotic demyelination risk 1
• Failing to identify and treat the underlying cause results in recurrence 1, 2
• Overly rapid correction exceeding 8 mmol/L in 24 hours causes osmotic demyelination syndrome 1, 3

Monitoring Requirements

• Severe symptoms: check serum sodium every 2 hours during initial correction 1
• After symptom resolution: check every 4 hours 1
• Mild to moderate cases: check daily until stable 1, 2
• Monitor for signs of osmotic demyelination syndrome for 7 days after correction 1