How to manage hyponatremia (low sodium levels) in patients?

Management of Hyponatremia

The management of hyponatremia should be guided by severity, symptoms, and volume status, with correction rates not exceeding 8 mmol/L in 24 hours (4-6 mmol/L for high-risk patients) to prevent osmotic demyelination syndrome. 1

Classification and Assessment

Hyponatremia is defined as serum sodium <135 mEq/L and classified by severity:

• Mild: 126-135 mEq/L
• Moderate: 120-125 mEq/L
• Severe: <120 mEq/L 1

Initial Evaluation

1. Determine if hyponatremia is hypotonic (most common) or non-hypotonic
2. Assess volume status to categorize as:
   • Hypovolemic (fluid deficit)
   • Euvolemic (normal fluid status)
   • Hypervolemic (fluid overload) 1, 2
3. Measure urine osmolality and sodium to determine cause
4. Evaluate for symptoms:
   • Mild symptoms: nausea, weakness, headache, cognitive deficits
   • Severe symptoms: somnolence, seizures, coma, cardiorespiratory distress 1, 2

Treatment Algorithm Based on Severity and Symptoms

1. Severely Symptomatic Hyponatremia (Medical Emergency)

• Administer 3% hypertonic saline as 100-150 mL bolus or continuous infusion 1, 2, 3
• Target initial correction: 4-6 mEq/L within 1-2 hours to reverse encephalopathy
• Do not exceed 10 mEq/L in first 24 hours 2
• Monitor serum sodium every 4-6 hours during active correction 1

2. Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment based on volume status:

Hypovolemic Hyponatremia

• Normal saline (0.9% NaCl) infusion to restore volume 4
• Address underlying cause (diuretics, GI losses, etc.)

Euvolemic Hyponatremia (often SIADH)

• Fluid restriction to 1,000-1,500 mL/day for mild cases (126-135 mEq/L) 1
• Stricter fluid restriction (1,000 mL/day) for moderate cases (120-125 mEq/L) 1
• Very strict fluid restriction for severe cases (<120 mEq/L) 1
• Consider pharmacologic options if fluid restriction fails:
  • Tolvaptan: Starting at 15 mg once daily, can increase to 30 mg after 24 hours (maximum 60 mg daily) 1, 5
  • Urea: Effective second-line therapy for SIADH 3
  • Salt tablets to increase solute intake 4

Hypervolemic Hyponatremia

• Fluid restriction as primary approach 1, 4
• Loop diuretics to reduce fluid overload 6
• Tolvaptan may be considered for heart failure patients 1, 5
• Albumin infusion may be considered in cirrhosis 1
• Treat underlying condition (heart failure, cirrhosis) 4

Critical Considerations and Pitfalls

Correction Rate

• Do not exceed 8 mmol/L in 24 hours for standard patients 1
• Limit to 4-6 mmol/L in 24 hours for high-risk patients (alcoholism, liver disease, malnutrition) 1
• Overly rapid correction can cause osmotic demyelination syndrome, presenting 2-7 days after correction with dysarthria, dysphagia, and oculomotor dysfunction 1, 2

Monitoring

• Check serum sodium every 4-6 hours during active correction 1
• Be prepared to slow correction if rate exceeds recommendations
• Consider desmopressin to halt water diuresis if overcorrection occurs 1

Special Populations

• Cirrhosis patients: Avoid hypertonic saline unless life-threatening symptoms present 1
• Endurance athletes with exercise-associated hyponatremia: Treat according to symptoms 1
• Children: Require special attention due to larger brain-to-skull ratio 1

Tolvaptan Considerations

• Requires hospitalization for initiation when sodium <120 mEq/L 1
• May interact with CYP3A substrates and P-gp substrates 5
• Can increase digoxin levels by 30% (Cmax) and 20% (AUC) 5
• May increase risk of gastrointestinal bleeding in cirrhosis patients 1

By following this structured approach to hyponatremia management based on severity, symptoms, and volume status, while carefully monitoring correction rates, clinicians can effectively treat this common electrolyte disorder while minimizing the risk of complications.