What is the algorithm for managing hyponatremia?

Algorithm for Managing Hyponatremia

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

Initial Assessment and Classification

• Hyponatremia is defined as serum sodium <135 mmol/L and should be classified by severity: mild (126-135 mEq/L), moderate (120-125 mEq/L), and severe (<120 mEq/L) 1
• Initial workup should include serum and urine osmolarity, urine electrolytes, uric acid, and assessment of extracellular fluid volume status to determine the underlying cause 1
• Categorize patients according to volume status: hypovolemic, euvolemic, or hypervolemic hyponatremia 2
• A spot urine sodium <30 mmol/L suggests hypovolemic hyponatremia (positive predictive value 71-100% for response to 0.9% saline), while >20 mEq/L with high urine osmolality (>500 mosm/kg) suggests SIADH 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (seizures, coma)

• Administer 3% hypertonic saline with an initial goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve 1
• Calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1
• Initial infusion rate (ml/kg per hour) can be estimated by: body weight (kg) × desired rate of increase in sodium (mmol/L per hour) 3
• Do not exceed total correction of 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1
• Consider ICU admission for close monitoring during treatment 1

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

• Treatment approach depends on volume status and underlying cause 1, 4
• Monitor serum sodium levels every 4-6 hours during active correction 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

• Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion 1, 4
• For severe dehydration with neurological symptoms, consider hypertonic saline with careful monitoring 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1L/day is the cornerstone of treatment for mild/asymptomatic cases 1, 4
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction 1
• Consider pharmacological options for resistant cases 1:
  • Urea
  • Diuretics
  • Vasopressin receptor antagonists (tolvaptan, conivaptan)
  • Demeclocycline or lithium (less commonly used due to side effects)

Hypervolemic Hyponatremia (cirrhosis, heart failure)

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

Correction Rate Guidelines

• Maximum increase of 8 mmol/L in 24 hours for most patients to prevent osmotic demyelination syndrome 1
• For patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy, use more cautious correction (4-6 mmol/L per day) due to higher risk of osmotic demyelination 1
• If overcorrection occurs, consider relowering with electrolyte-free water or desmopressin 1

Special Considerations

Neurosurgical Patients

• Distinguish between SIADH and cerebral salt wasting (CSW), as treatment approaches differ significantly 1
• For CSW, treatment focuses on volume and sodium replacement, not fluid restriction 1
• Fludrocortisone may be considered 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 in cirrhosis increases risk for hepatic encephalopathy, hepatorenal syndrome, and spontaneous bacterial peritonitis 1
• Fluid restriction may prevent further decrease in serum sodium but rarely improves it significantly 1
• Consider albumin infusion alongside fluid restriction 1

Monitoring and Follow-up

• For severe symptoms: monitor serum sodium every 2 hours during initial correction 1
• After resolution of severe symptoms, check sodium every 4-6 hours 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

• Overly rapid correction of chronic hyponatremia leading to osmotic demyelination syndrome 1
• Inadequate monitoring during active correction 1
• Using fluid restriction in CSW (can worsen 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 (135 mmol/L) as clinically insignificant 1