What volume of 7.5% sodium bicarbonate injection should be administered to achieve an 8.4% dose in 5% Dextrose over 4 hours?

Sodium Bicarbonate Dose Calculation: 7.5% to 8.4% Equivalent

To deliver an equivalent dose of 8.4% sodium bicarbonate using a 7.5% solution, you need to administer approximately 28 mL of the 7.5% solution for every 25 mL of 8.4% solution prescribed, diluted in 5% dextrose (D5W) and infused over 4 hours.

Calculation Method

The calculation is based on the total milliequivalents (mEq) of sodium bicarbonate needed:

• 8.4% sodium bicarbonate = 1 mEq/mL 1, 2
• 7.5% sodium bicarbonate = 0.9 mEq/mL 2

Step-by-Step Calculation

For a standard 25 mL dose of 8.4% solution:

• Total mEq needed = 25 mL × 1 mEq/mL = 25 mEq 1
• Volume of 7.5% needed = 25 mEq ÷ 0.9 mEq/mL = 27.8 mL (round to 28 mL) 2

Preparation and Administration

Dilution in D5W:

• Sodium bicarbonate should be diluted in 5% dextrose injection (D5W) for infusion 3, 4
• The diluted solution is stable for up to 7 days when refrigerated at 2-4°C, or up to 30-48 hours at room temperature depending on concentration 4

Infusion Rate:

• Administer the calculated volume over 4 hours as prescribed 1
• Use a dedicated IV line when possible, as sodium bicarbonate should not be mixed with catecholamines or calcium in the same line 3, 1

Critical Safety Considerations

Concentration Precautions:

• Only the 0.5 mEq/mL concentration should be used for newborn infants; dilution of available stock solutions may be necessary 1, 3
• Do not confuse the two concentrations (7.5% vs 8.4%) when calculating doses, as this could result in under-dosing 1, 2

Incompatibilities:

• Do not mix sodium bicarbonate with vasoactive amines (catecholamines) or calcium, as adrenergic agents are inactivated in alkaline solutions 1, 3
• Use separate IV lines or ensure adequate barrier fluid (≥2 mL) if concurrent administration is necessary 5

Monitoring:

• Monitor serum sodium levels, as large volumes of dextrose with sodium bicarbonate can cause hypernatremia or hyponatremia depending on the clinical context 6
• Effective ventilation must be established before sodium bicarbonate administration to allow elimination of excess CO2 produced by bicarbonate 1, 3

Common Pitfall

The most common error is failing to account for the concentration difference between the two formulations. Always calculate based on total mEq required rather than volume-for-volume substitution 1, 2.