Skip to main content

Transforming the Venous Blood Gas to the Arterial Blood Gas

About this Calculator

The VBG → ABG calculator estimates arterial blood gas parameters from venous blood gas values using regression-derived formulas. Venous blood gases are often easier to obtain and less invasive than arterial sampling, but arterial values remain the reference for acid–base and respiratory assessment. This tool converts venous pH, pCO₂, and optionally HCO₃⁻ into estimated arterial equivalents for clinical guidance when direct arterial measurement is unavailable.

epCO₂ = 0.9224 × vpCO₂ − 3.642
epH = 1.023 × vpH − 0.1224
eHCO₃⁻ (H-H) = 0.0307 × epCO₂ × 10(epH − 6.095)
eHCO₃⁻ (direct) = 0.9436 × vHCO₃⁻ − 0.04011 — when venous HCO₃⁻ provided

Interpretation of Results

  • Estimated Arterial pH: Normal range 7.35–7.45. Low values suggest acidosis; high values suggest alkalosis.

  • Estimated Arterial pCO₂: Normal range 35–45 mmHg. Elevated values suggest respiratory acidosis or compensatory response to metabolic alkalosis; low values suggest respiratory alkalosis or compensation for metabolic acidosis.

  • Estimated Arterial HCO₃⁻: Normal range 22–26 mEq/L. Use the Henderson–Hasselbalch–derived value when venous HCO₃⁻ is not provided; when it is, both H-H and direct regression estimates are shown for comparison.

  • Limits of Agreement: 95% limits of agreement for arterial pH are −0.05 to +0.04 units; for pCO₂, −5.6 to +5.5 mmHg. These estimates provide clinical guidance but do not replace direct arterial blood gas measurement when clinically indicated.

Reference

Batlle D, Fischer R, Hassler L, Rehman Z, Rehman U, Araujo G, Rivero C, Gomez L, Parry N, Wysocki J, Liebowitz D, Rosa R. Transforming the Venous Blood Gas to the Arterial Blood Gas from Concurrent Measurements. Kidney360. 2026 Jan 2. doi: 10.34067/KID.0000001113. PMID: 41481367. View on PubMed.

—
mmHg
mEq/L
Estimated Arterial Blood Gas
Estimated arterial pH —
Estimated arterial pCO₂ — mmHg
Estimated arterial HCO₃⁻ (H-H) — mEq/L
 
95% Limits of Agreement
Arterial pH: −0.05 to +0.04
Arterial pCO₂: −5.6 to +5.5 mmHg
Arterial HCO₃⁻ (H-H): −2.29 to +1.96 mEq/L
Arterial HCO₃⁻ (direct): −2.31 to +1.83 mEq/L
Formulas (Batlle et al., Kidney360, 2026; n = 5,419)
epCO₂ = 0.9224 × vpCO₂ − 3.642
epH = 1.023 × vpH − 0.1224
eHCO₃⁻ = 0.9436 × vHCO₃⁻ − 0.04011
eHCO₃⁻ (H-H) = 0.0307 × epCO₂ × 10(epH − 6.095)
Note: These estimates provide clinical guidance but do not replace direct arterial blood gas measurement when clinically indicated.
ukidneyisup