What is the bicarbonate deficit formula?

The deficit in mmol equals the distribution factor times body weight in kilograms times the difference between target and measured bicarbonate. A common form is 0.5 × weight × (target HCO₃ − measured HCO₃), with the factor representing the apparent bicarbonate space.

Why does the distribution factor vary from 0.4 to 0.5?

The apparent volume of bicarbonate distribution is not fixed. In mild acidosis about 0.4 to 0.5 of body weight is used, but in severe acidosis the apparent space expands, so a higher factor (up to 0.8 in extreme cases) better reflects the buffering across cells and bone.

When is bicarbonate replacement appropriate?

IV sodium bicarbonate is generally reserved for severe metabolic acidosis, typically a pH below about 7.1 to 7.2, especially with normal-anion-gap (loss) acidosis such as renal tubular acidosis or diarrhoea. In lactic and ketoacidosis, treating the cause is usually preferred.

Is my data stored anywhere?

No. The calculation runs entirely in your browser and nothing you enter is transmitted or saved on any server.

Bicarbonate Deficit Calculator

Q: Should the full deficit be replaced at once?

No. It is usual to give only part of the calculated deficit, often half, then recheck the blood gas and recalculate. Rapid full correction risks overshoot, hypokalaemia, hypocalcaemia, sodium and volume overload, and paradoxical CSF acidosis.

The bicarbonate deficit calculator estimates how much bicarbonate must be replaced to raise a patient’s serum HCO₃ toward a target value in severe metabolic acidosis. It is a planning tool for IV sodium bicarbonate dosing in nephrology and emergency medicine.

How it works

The deficit in millimoles is the apparent distribution volume of bicarbonate multiplied by the gap between the target and measured concentration:

Deficit (mmol) = factor × weight(kg) × (target HCO3 − measured HCO3)

The factor is the fraction of body weight that approximates the bicarbonate space — conventionally 0.4 to 0.5. Because bicarbonate is buffered across cells and bone, the apparent space expands as acidosis worsens, so a higher factor (up to about 0.8) is sometimes used when the measured HCO₃ is very low.

One ampoule of 8.4% sodium bicarbonate contains about 50 mmol in 50 mL, which helps translate the deficit into a number of ampoules.

Example and notes

For a 70 kg patient with a measured HCO₃ of 10 mmol/L and a target of 18 mmol/L, using a factor of 0.5: 0.5 × 70 × (18 − 10) = 280 mmol, roughly 5.6 ampoules of 8.4% solution.

Replace only part of the deficit (often half), then recheck the blood gas and recalculate. Rapid full correction risks overshoot, hypokalaemia, hypocalcaemia, sodium and volume overload, and paradoxical CSF acidosis. Treating the underlying cause is usually preferred in lactic acidosis and ketoacidosis.