How to manage hyponatremia?

Management of Hyponatremia

The management of hyponatremia should be based on volume status assessment, symptom severity, and underlying cause, with correction rates not exceeding 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Initial Assessment and Classification

• Hyponatremia is defined as serum sodium <135 mmol/L and classified as mild (126-135 mmol/L), moderate (120-125 mmol/L), or severe (<120 mmol/L) 1, 2
• Initial workup should include serum and urine osmolality, urine electrolytes, uric acid, and assessment of extracellular fluid volume status to determine the underlying cause 1
• Urinary sodium <30 mmol/L suggests hypovolemic hyponatremia, while >20 mEq/L with high urine osmolality (>500 mosm/kg) suggests SIADH 1
• Even mild hyponatremia is associated with cognitive impairment, gait disturbances, increased falls and fractures 3

Treatment Based on Volume Status

Hypovolemic Hyponatremia

• Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion 1, 2
• For severe dehydration with neurological symptoms, consider hypertonic saline with careful monitoring 1

Euvolemic Hyponatremia (SIADH)

• Implement fluid restriction to 1 L/day as first-line treatment 1, 2
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction 1
• Consider pharmacological options for resistant cases: urea, diuretics, lithium, demeclocycline 1, 4

Hypervolemic Hyponatremia (e.g., cirrhosis, heart failure)

• Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 1, 2
• Consider albumin infusion for patients with cirrhosis 1
• Avoid hypertonic saline unless life-threatening symptoms are present 1

Treatment Based on Symptom Severity

Severe Symptoms (seizures, coma)

• Administer 3% hypertonic saline with an initial goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve 1, 5
• Can be given as boluses of 100 mL over 10 minutes, repeated up to three times at 10-minute intervals until symptoms improve 1
• Total correction should not exceed 8 mmol/L in 24 hours 1, 6

Mild/Asymptomatic Cases

• Fluid restriction to 1 L/day for euvolemic or hypervolemic hyponatremia 1, 2
• For hypovolemic cases, isotonic saline for volume repletion 1, 7
• Treat underlying cause (discontinue offending medications, manage heart failure, etc.) 1, 3

Correction Rate Guidelines

• Maximum increase of 8 mmol/L in 24 hours for most patients to prevent osmotic demyelination syndrome 1, 4
• For patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy, use more cautious correction (4-6 mmol/L per day) 1, 2
• Calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1

Special Considerations

Neurosurgical Patients

• Distinguish between SIADH and cerebral salt wasting (CSW) as treatment approaches differ significantly 1
• CSW requires volume and sodium replacement, not fluid restriction 1
• Consider fludrocortisone for hyponatremia in subarachnoid hemorrhage patients at risk of vasospasm 1
• Avoid fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1

Cirrhotic Patients

• Hyponatremia reflects worsening hemodynamic status and increases risk for hepatic encephalopathy, hepatorenal syndrome, and spontaneous bacterial peritonitis 1
• Tolvaptan use in cirrhotic patients is associated with higher risk of gastrointestinal bleeding (10% vs 2% in placebo) 8

Pharmacological Options

Vasopressin Receptor Antagonists (Vaptans)

• Consider for euvolemic or hypervolemic hyponatremia resistant to fluid restriction 1, 4
• Monitor closely to avoid overly rapid correction 1
• Side effects include thirst, dry mouth, increased urination, and risk of hypernatremia 8

Hypertonic Saline (3% NaCl)

• Reserved primarily for severe symptomatic hyponatremia 1, 9
• Can increase regional cerebral blood flow, brain tissue oxygen, and pH in patients with subarachnoid hemorrhage 1

Monitoring and Follow-up

• For severe symptoms: monitor serum sodium every 2 hours during initial correction 1
• For mild/moderate cases: daily monitoring until stable 2
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1
• If overcorrection occurs, consider relowering with electrolyte-free water or desmopressin 1

Common Pitfalls to Avoid

• Overly rapid correction of chronic hyponatremia leading to osmotic demyelination syndrome 1, 2
• Inadequate monitoring during active correction 1
• Using fluid restriction in CSW (can worsen outcomes) 1, 2
• Failing to recognize and treat the underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1, 2
• Ignoring mild hyponatremia (135 mmol/L) as clinically insignificant 1