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Bicarbonate Deficit

Bicarbonate deficit = 0.5 × weight (kg) × (target − measured HCO₃) mmol. Give about half over several hours and recheck; the apparent bicarbonate space rises as HCO₃ falls (0.4 + 2.6/HCO₃).

Weight (kg or lb)
Serum bicarbonate (HCO₃⁻) (mmol/L or mEq/L)
Target HCO₃⁻ (mmol/L or mEq/L)

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Interpretation

Result	Meaning
> 0	Deficit to replace (partially, with re-measurement)

Formula

HCO₃ deficit (mmol) = 0.5 × weight (kg) × (target HCO₃ − measured HCO₃). Variable space: (0.4 + 2.6 ÷ HCO₃) × weight × (target − measured).

Clinical pearls

Bicarbonate therapy is not routinely beneficial in lactic acidosis or DKA; evidence supports it mainly for severe acidaemia with AKI, some toxicities (TCA, salicylate) and NAGMA from bicarbonate loss.
Watch for hypokalaemia, hypocalcaemia, volume and sodium load, and rising pCO₂ if ventilation is fixed.

Examples

bicarbonate deficit 70 kg hco3 10 bicarb deficit 80kg bicarbonate 6 target 15 how much sodium bicarbonate for a 60 kg patient with HCO3 8

FAQ

How do you calculate sodium bicarbonate dose?

Deficit ≈ 0.5 × weight × (target − measured HCO₃); typically half is given initially and the rest guided by repeat blood gases.

Why does the bicarbonate space increase in severe acidosis?

More of the added bicarbonate is consumed by intracellular and bone buffers, so the apparent distribution space rises as HCO₃ falls.

Evidence

Fernandez PC, Cohen RM, Feldman GM. The concept of bicarbonate distribution space: the crucial role of body buffers. Kidney Int 1989;36:747–52.

Nephrology & Electrolytes · Reviewed 2026-10-14 · Methodology