How to manage a patient with hyponatremia and elevated urine sodium?

Management of Hyponatremia with Elevated Urine Sodium

For a patient with hyponatremia and elevated urine sodium, treatment should be based on volume status assessment, with fluid restriction for SIADH and sodium/volume replacement for cerebral salt wasting. 1

Initial Assessment

• Evaluate volume status (hypovolemic, euvolemic, or hypervolemic) as this is critical for determining the underlying cause and appropriate treatment 1
• Check serum osmolality (typically <275 mosm/kg in hypoosmolar hyponatremia) 2
• Measure urine osmolality (>300 mosm/kg suggests impaired free water excretion) 2
• Elevated urine sodium (>20-40 mEq/L) with hyponatremia suggests either SIADH or cerebral salt wasting (CSW) 2, 1
• Rule out hypothyroidism, adrenal insufficiency, and medications that can cause hyponatremia 1

Diagnosis Based on Clinical Features

SIADH Diagnostic Criteria:

• Hyponatremia (serum sodium <134 mEq/L) 2
• Hypoosmolality (plasma osmolality <275 mosm/kg) 2
• Inappropriately high urine osmolality (>500 mosm/kg) 2
• Inappropriately high urinary sodium concentration (>20 mEq/L) 2
• Absence of hypothyroidism, adrenal insufficiency, or volume depletion 2
• Serum uric acid <4 mg/dL (has 73-100% positive predictive value for SIADH) 1

Differentiating SIADH from Cerebral Salt Wasting:

• SIADH: Euvolemic or mildly hypervolemic 1
• CSW: Hypovolemic with evidence of dehydration 1
• Fractional excretion of urate can help differentiate with 95% accuracy 2

Treatment Based on Volume Status and Severity

For Euvolemic Hyponatremia (SIADH):

• Mild/Asymptomatic (Na 126-135 mEq/L):

  • Free water restriction (<1 L/day) is first-line treatment 2, 1
  • Continue to monitor serum electrolytes closely 1

• Moderate (Na 120-125 mEq/L):

  • More strict fluid restriction (1-1.5 L/day) 1
  • Consider oral sodium chloride supplementation (100 mEq three times daily) if no response to fluid restriction 1
  • Monitor sodium levels every 4-6 hours initially 1

• Severe (Na <120 mEq/L) or Symptomatic:

  • For severe symptoms (seizures, coma): 3% hypertonic saline with goal to increase sodium by 6 mmol/L over 6 hours or until symptoms resolve 1, 3
  • Maximum correction should not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 4
  • Consider ICU admission for close monitoring 1
  • Pharmacologic options for resistant cases include:
    • Vasopressin receptor antagonists (tolvaptan) 5
    • Demeclocycline 2
    • Urea 1
    • Lithium (less commonly used due to side effects) 1

For Hypovolemic Hyponatremia (Cerebral Salt Wasting):

• Primary approach:

  • Volume repletion with isotonic (0.9%) saline 1
  • Avoid fluid restriction as it can worsen outcomes 1

• For severe symptoms:

  • 3% hypertonic saline and fludrocortisone 1
  • Monitor serum sodium every 2 hours during initial correction 1

For Hypervolemic Hyponatremia:

• Moderate to severe (Na <125 mEq/L):
  • Fluid restriction to 1-1.5 L/day 1
  • Consider albumin infusion for patients with cirrhosis 1
  • Avoid hypertonic saline unless life-threatening symptoms are present 1

Correction Rate Guidelines

• Standard correction rate: Maximum 8 mmol/L in 24 hours 1, 6
• High-risk patients: More cautious correction (4-6 mmol/L per day) for patients with:
  • Advanced liver disease
  • Alcoholism
  • Malnutrition
  • Prior encephalopathy 1
• For severe symptoms: Initial goal to correct 6 mmol/L over 6 hours or until symptoms resolve 1, 7

Monitoring During Treatment

• For severe symptoms: Monitor serum sodium every 2 hours during initial correction 1
• After resolution of severe symptoms: Monitor every 4-6 hours 1
• Calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1
• If overcorrection occurs, consider relowering with electrolyte-free water or desmopressin 1, 6

Common Pitfalls to Avoid

• Using fluid restriction in cerebral salt wasting (can worsen outcomes) 1
• Overly rapid correction exceeding 8 mmol/L in 24 hours (risk of osmotic demyelination syndrome) 1, 8
• 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 (135 mmol/L) as clinically insignificant 1

Special Considerations

• Patients with subarachnoid hemorrhage at risk for vasospasm should not be treated with fluid restriction 1
• Even mild hyponatremia may be associated with neurocognitive problems, including falls and attention deficits 1, 4
• Hyponatremia in patients with SCLC is associated with shortened survival 2