Arterial Blood Gas Calculator

What to compute

PaCO2 (mmHg)

Bicarbonate (HCO3-) (mmol/L)

For a respiratory disorder, is it acute or chronic?

Sodium (mmol/L)

Chloride (mmol/L)

Serum albumin (g/dL)The anion gap is corrected upward by 2.5 mmol/L for each 1 g/dL below 4.0.

For a high-anion-gap acidosis, which kind?Berend 2014 uses the full rise in the anion gap for ketoacidosis and 0.6 times it for lactic acidosis.

PaO2 (mmHg)

Inspired oxygen fraction (FiO2)As a fraction: 0.21 is room air.

Barometric pressure (mmHg)Sea level is 760 mmHg; altitude lowers it and lowers the alveolar PO2 with it.

Respiratory quotient (R)

Age (years)

Haemoglobin (g/dL)

Arterial oxygen saturation (SaO2) (%)

Hufner's constant (mL O2/g Hb)Quoted between 1.34 and 1.39 depending on the source; it is an input so the choice is visible.

Dissolved oxygen coefficient (mL O2/dL/mmHg)

Mean airway pressure (cmH2O)Oxygenation index only.

Primary acid-base disorder

Metabolic acidosis

Arterial Blood Gas (ABG) Calculator

Expected compensation

Winters: expected PaCO2 = 1.5 x 10 + 8 = 23 +/- 2 mmHg

Is the compensation appropriate?

Measured PaCO2 24 lies inside the expected 21-25: appropriate compensation, no second disorder implied.

Anion gap

30.0 mmol/L

Albumin-corrected anion gap

30.0 mmol/L

Delta-delta

4.0 mmol/L

What the delta-delta says

Between -5 and +5: a pure high-anion-gap metabolic acidosis.

pH implied by HCO3 and PaCO2

7.243

Alveolar PO2 (PAO2)

119.7 mmHg

A-a difference

29.7 mmHg

Age-expected A-a difference

14.0 mmHg

PaO2 / FiO2

428.6 mmHg

Berlin ARDS category by P/F

Above the Berlin ARDS P/F threshold of 300 mmHg

Arterial oxygen content (CaO2)

18.47 mL O2/dL

Oxygenation index

2.80

Worked out from Berend K, de Vries APJ, Gans ROB. Physiological approach to assessment of acid-base disturbances and 4 other sources.

The reference range for the anion gap is analyser-specific and is reported anywhere from 3-12 to 8.5-15 mmol/L; use your own laboratory's range rather than a textbook one.

An arithmetic aid to reading a blood gas, not an interpretation of a patient. Compensation formulas are empirical population rules with wide bands, laboratory reference ranges differ between analysers, and a normal-looking gas can hide two opposing disorders. Clinical interpretation belongs to a clinician with the patient in front of them.

How this is worked out

7 steps

pH 7.24 against the reference 7.40 +/- 0.02: acidaemia.
PaCO2 24 mmHg, HCO3 10 mmol/L. Primary disorder: Metabolic acidosis.
Winters: expected PaCO2 = 1.5 x 10 + 8 = 23 +/- 2 mmHg
Measured PaCO2 24 lies inside the expected 21-25: appropriate compensation, no second disorder implied.
Anion gap = Na - (Cl + HCO3) = 140 - (100 + 10) = 30 mmol/L.
Albumin is 4.0 g/dL, so no correction is needed.
Henderson-Hasselbalch check: 6.1 + log10(10 / (0.03 x 24)) = 7.243.

Results are general information, not financial, tax, legal, medical or engineering advice.