What is the formula for correcting severe hyponatremia?

Formula for Correcting Severe Hyponatremia

For severe symptomatic hyponatremia, correction should not exceed 8 mEq/L in 24 hours to prevent osmotic demyelination syndrome, with hypertonic saline (3%) administered as boluses to increase serum sodium by 4-6 mEq/L within 1-2 hours for immediate symptom relief. 1, 2

Assessment and Classification

Before initiating treatment, classify the patient's hyponatremia based on volume status:

• Hypovolemic hyponatremia: Normal saline infusion
• Hypervolemic hyponatremia: Fluid restriction and treatment of underlying condition
• Euvolemic hyponatremia (SIADH): Consider tolvaptan starting at 15 mg once daily 1

Correction Formula and Rates

For Severe Symptomatic Hyponatremia (seizures, coma, cardiorespiratory distress)

1. Initial bolus of 3% hypertonic saline to raise sodium by 4-6 mEq/L within 1-2 hours 1, 2
2. Maximum correction:
   • Standard risk patients: ≤8 mEq/L in 24 hours 1
   • High-risk patients: <8 mEq/L in 24 hours 3

High-Risk Patients for Osmotic Demyelination

• Patients with initial serum sodium <115 mEq/L
• Alcoholism
• Malnutrition
• Liver disease
• Hypokalemia 1, 3

Monitoring Protocol

• Check serum sodium every 2-4 hours initially
• Then every 4-6 hours once stabilized
• Monitor vital signs every 1-2 hours initially
• Daily renal function tests and electrolytes with each sodium check 1

Prevention of Overcorrection

Recent evidence suggests that overly slow correction (<6 mEq/L per 24 hours) may be associated with increased mortality and longer hospital stays 4. However, the risk of osmotic demyelination syndrome remains a serious concern with rapid correction.

If correction is proceeding too rapidly:

1. Consider administering desmopressin (DDAVP) to prevent further correction 5
2. Three strategies for desmopressin use:
   • Proactive: Administer early based on initial sodium concentration
   • Reactive: Administer based on changes in sodium or urine output
   • Rescue: Administer after correction targets are exceeded 5

Special Considerations

For patients with liver disease and hyponatremia:

• Immediately discontinue all diuretics, especially if serum sodium <120 mmol/L
• For hypervolemic hyponatremia with ascites, consider large volume paracentesis with albumin replacement
• Fluid restriction to 1-1.5 L/day and sodium restriction 1

Common Pitfalls to Avoid

1. Overly rapid correction: Despite following the 8-10 mEq/L per day guideline, osmotic demyelination can still occur, especially in high-risk patients with initial sodium <115 mEq/L 3

2. Overly slow correction: Very slow correction (<4-6 mEq/L per 24 hours) has been associated with increased mortality and longer hospital stays in recent research 4

3. Failure to recognize risk factors: Patients with alcoholism, malnutrition, liver disease, or hypokalemia require more cautious correction 1, 3

4. Inadequate monitoring: Frequent sodium checks are essential, especially in the first 24-48 hours of treatment 1

5. Failure to adjust treatment: If correction is proceeding too rapidly, be prepared to administer desmopressin and/or hypotonic fluids to slow the rate 5, 6