Bicarbonate Deficit Calculator (mmol/mEq) with Sodium Bicarbonate Dose and Volume
Estimate the bicarbonate deficit in metabolic acidosis with the fixed 0.3/0.4/0.5 × weight space, the dynamic Kurtz or Kollef space, or the base-deficit method; choose actual or ideal body weight, the share to give first and the product (8.4%, 4.2%, 1.4%, 1.26%), and get the dose, volume, 50 mL ampoules, infusion rate and sodium load.
How it works
Deficit (mmol) = space factor × weight (kg) × (target HCO₃⁻ − current HCO₃⁻) · factor: fixed 0.3, 0.4 or 0.5 L/kg; Kurtz 0.4 + 2.6 ÷ HCO₃⁻; Kollef 0.4 + 2.4 ÷ HCO₃⁻ · base-deficit method: 0.3 × weight × base deficit · volume = dose ÷ concentration (8.4% = 1 mmol/mL)
The bicarbonate deficit is the amount of alkali that would raise the serum bicarbonate to the target if it spread through an apparent "bicarbonate space". That space is bigger than the extracellular fluid, because buffers in cells and bone take up part of each dose, and it grows as acidosis deepens: about 0.4–0.5 L/kg in moderate acidosis and 0.7 L/kg or more when bicarbonate is very low. Fixed factors (0.3, 0.4 or 0.5 × weight) are the classic textbook versions; the dynamic formulas of Kurtz (0.4 + 2.6 ÷ HCO₃⁻) and Kollef (0.4 + 2.4 ÷ HCO₃⁻) let the space grow as bicarbonate falls. The base-deficit method (0.3 × weight × base deficit) uses the base excess from the blood gas instead of the serum bicarbonate. The result is only an estimate. Ongoing acid production or bicarbonate loss changes the requirement, and bicarbonate generates CO₂, loads sodium and volume, and lowers potassium and ionised calcium. The usual approach is to give half (or less) of the calculated deficit over a few hours, recheck the gas and electrolytes, and decide on more. Evidence supports bicarbonate mainly for severe normal-anion-gap acidosis, severe hyperkalaemia, certain poisonings and, from the BICAR-ICU trial, severe acidaemia with acute kidney injury.
Worked example
A 75 kg patient with bicarbonate 10 mmol/L, target 24, dynamic Kurtz space: factor = 0.4 + 2.6 ÷ 10 = 0.66 L/kg, so the space is 49.5 L and the deficit is 49.5 × (24 − 10) = 693 mmol. Half the deficit is 347 mmol, which is 347 mL of 8.4% sodium bicarbonate (6.9 ampoules of 50 mL), given over 4 hours at 86.6 mL/h; it carries 347 mmol of sodium, as much as 2.25 L of 0.9% saline. With the classic fixed 0.5 × weight the deficit would be 525 mmol, and with 0.4 × weight 420 mmol.
Sources: Sodium bicarbonate deficit calculator: Kurtz, Kollef, Ewald, Ghosh formulas and dosing guidance (GlobalRPH) · Bicarbonate deficit calculator (Omni Calculator) · Formulas: bicarbonate deficit = 0.4 × weight × (24 − HCO₃⁻) (WikEM)
Frequently asked questions
How do you calculate a bicarbonate deficit?
Multiply the bicarbonate space by the rise you want: deficit = factor × weight × (target − current HCO₃⁻). With the classic factor of 0.5, a 70 kg patient going from 12 to 18 mmol/L needs 0.5 × 70 × 6 = 210 mmol. Dynamic formulas use a larger factor when bicarbonate is very low.
Should I give the whole deficit?
Usually not. The common practice is to give about half over 3–4 hours, recheck the blood gas and electrolytes, and then decide. Full rapid correction can overshoot into alkalosis, lower potassium and ionised calcium, and cause fluid and sodium overload.
What target bicarbonate should I use?
The formula traditionally uses 24 mmol/L, but most protocols aim first for 12–15 mmol/L or a pH above 7.2, because the underlying cause usually corrects the rest. Use a lower target in the calculator to see a more realistic first dose.
How many mL of 8.4% sodium bicarbonate is that?
8.4% sodium bicarbonate contains 1 mmol per mL, so the dose in mmol equals the volume in mL. A 50 mL ampoule holds 50 mmol. 4.2% has 0.5 mmol/mL, 1.4% about 0.167 mmol/mL and 1.26% 0.15 mmol/mL.
Is bicarbonate used in DKA or lactic acidosis?
Not routinely. Insulin and fluids correct diabetic ketoacidosis, and guidelines reserve bicarbonate for pH below about 6.9–7.0. In lactic acidosis, treating the cause is the priority; bicarbonate has not been shown to improve outcomes except in selected patients with acute kidney injury.
Are mmol and mEq the same for bicarbonate?
Yes. Bicarbonate has a single charge, so 1 mmol equals 1 mEq.
Related calculators
Clinical decision tool for education and for use by trained clinicians alongside judgement, not a prescription. Bicarbonate therapy is controversial outside specific indications; dose, product, route and rate must follow local protocols, and the patient must be reassessed with repeat blood gases and electrolytes.