What volume of 3% (three percent) hypertonic saline is required to correct a sodium level by 6 mmol/L over 6 hours?

Calculating 3% Hypertonic Saline Volume for Sodium Correction

To correct a sodium level by 6 mmol/L over 6 hours using 3% hypertonic saline, you need approximately 100 mL of 3% hypertonic saline for every 2 mmol/L increase in serum sodium desired in an average adult.

Calculation Method

• The goal is to increase serum sodium by 6 mmol/L over 6 hours, which aligns with the recommended initial correction goal for severe symptomatic hyponatremia 1, 2
• 3% hypertonic saline contains 513 mEq/L of sodium (3g NaCl per 100mL = 513 mEq/L) 1
• For an average 70 kg adult:
  • 100 mL of 3% saline will raise serum sodium by approximately 2 mmol/L 1, 2
  • Therefore, 300 mL of 3% saline would be needed to raise sodium by 6 mmol/L 1, 2

Administration Guidelines

• Administer as 100 mL boluses over 10 minutes, which can be repeated up to three times at 10-minute intervals until symptoms improve 1
• Alternatively, administer as a continuous infusion over 6 hours 1, 3
• Monitor serum sodium every 2 hours during initial correction 1, 2
• Discontinue 3% saline once severe symptoms resolve or when the desired 6 mmol/L increase is achieved 3

Important Safety Considerations

• Do not exceed total correction of 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 3, 2
• After initial 6 mmol/L correction, limit to only 2 mmol/L in the following 18 hours 3
• Patients with advanced liver disease, alcoholism, or malnutrition require more cautious correction (4-6 mmol/L per day) 1, 2
• Consider ICU admission for close monitoring during treatment 1, 2

Weight-Based Calculation (More Precise)

• For more precise dosing, calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × body weight in kg) 1
• For a 70 kg patient wanting to increase by 6 mmol/L: 6 × (0.5 × 70) = 210 mEq sodium needed
• Since 3% saline contains 513 mEq/L, volume needed = 210 ÷ 513 = 0.41 L or approximately 410 mL 1, 4

Transition After Correction

• After severe symptoms resolve, switch to protocols for mild symptoms or asymptomatic hyponatremia 3
• Continue monitoring serum sodium levels every 4 hours instead of every 2 hours 3
• Implement fluid restriction to 1L/day for ongoing management 1, 3, 2

Common Pitfalls to Avoid

• Overly rapid correction exceeding 8 mmol/L in 24 hours can lead to osmotic demyelination syndrome 1, 3, 2
• Inadequate monitoring during active correction can miss dangerous trends in sodium levels 1
• Failing to recognize and treat the underlying cause of hyponatremia 1