Bicarbonate Deficit Calculator — Metabolic Acidosis
In metabolic acidosis, serum bicarbonate (HCO₃) falls below normal. This calculator estimates the total HCO₃ deficit using both the conservative ECF formula (0.4 × weight) and the broader TBW formula (0.6 × weight), and suggests a 50% initial replacement dose. Always interpret in the full clinical context.
kg
mEq/L
mEq/L
0.4 × weight (kg) × (target − actual HCO₃) — extracellular fluid correction factor
- 1
HCO₃ deficit
24 − 16 = 8Difference between target and actual serum bicarbonate. - 2
ECF bicarbonate deficit (0.4 × weight × deficit)
0.4 × 70 × 8 = 224
How does this calculator work?
HCO₃ deficit (mEq) = 0.4 × weight (kg) × (target − actual HCO₃). Give 50% of this as the initial IV NaHCO₃ dose, recheck blood gas, then recalculate. Normal HCO₃ is 22–26 mEq/L. The more aggressive TBW formula uses 0.6 instead of 0.4. Always treat the underlying cause.
Formula
How this is calculated
Metabolic acidosis is characterised by a serum bicarbonate below 22 mEq/L. In severe cases (HCO₃ < 10–12 mEq/L with haemodynamic compromise) clinicians sometimes administer intravenous sodium bicarbonate. The standard Astrup ECF formula is: Deficit = 0.4 × weight (kg) × (target − actual HCO₃). The factor 0.4 represents the approximate volume of distribution of bicarbonate in the extracellular fluid (~40% of body weight). An alternative Kassirer-Bleich formula uses 0.6 to reflect broader equilibration across total body water; it yields a more aggressive (higher) replacement dose.
In practice, no more than 50% of the calculated ECF deficit is given as the initial dose. Blood gas is then rechecked and the deficit recalculated. This staged approach prevents overshoot metabolic alkalosis, hypokalaemia, and a paradoxical leftward shift of the oxyhaemoglobin dissociation curve. Underlying causes — lactic acidosis, diabetic ketoacidosis, renal tubular acidosis — must always be treated simultaneously. IV sodium bicarbonate is generally not recommended for lactic acidosis unless pH < 7.10 with cardiovascular instability.
Frequently asked questions
Most guidelines reserve IV sodium bicarbonate for severe metabolic acidosis (HCO₃ < 10–12 mEq/L) with haemodynamic instability, specific conditions such as renal tubular acidosis, or severe hyperchloraemic acidosis. It is generally avoided in lactic acidosis and is not routine in diabetic ketoacidosis.
Blood bicarbonate changes as the underlying condition evolves and the body buffers the infused bicarbonate. Over-correction risks metabolic alkalosis, dangerous drops in serum potassium, and impaired oxygen delivery. Giving half the deficit, then reassessing, is the standard cautious approach.
The ECF formula (0.4 factor) restricts correction to the extracellular compartment and is more conservative. The TBW formula (0.6 factor) assumes bicarbonate equilibrates across total body water and gives a higher replacement dose. Most clinical protocols use the ECF formula as the starting point.
TG we-Calculate Editorial Team. (2026). Bicarbonate Deficit Calculator — Metabolic Acidosis [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/bicarbonate-deficit-calculator
TG we-Calculate Editorial Team. "Bicarbonate Deficit Calculator — Metabolic Acidosis." TG we-Calculate. 2026. https://we-calculate.com/calculator/bicarbonate-deficit-calculator.
TG we-Calculate Editorial Team, "Bicarbonate Deficit Calculator — Metabolic Acidosis," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/bicarbonate-deficit-calculator
@misc{wecalculate_bicarbonate_deficit_calculator, title = {Bicarbonate Deficit Calculator — Metabolic Acidosis}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/bicarbonate-deficit-calculator}}, year = {2026}, note = {TG we-Calculate} }
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