Arterial vs Venous Blood Gas

While arterial blood gases (ABGs) remain the gold standard for assessing oxygenation and acid-base balance, venous blood gases (VBGs) are increasingly used for trend monitoring and initial evaluation in stable patients.

Key Differences

Parameter	Arterial (ABG)	Venous (VBG)
Sampling Site	Radial, femoral, or brachial artery	Peripheral or central vein
pH	7.35–7.45	≈0.03–0.05 lower than arterial
PaCO₂	35–45 mmHg	≈4–6 mmHg higher than arterial
HCO₃⁻	22–29 mEq/L	Similar (within ±1–2 mEq/L)
O₂	PaO₂ 80–100 mmHg	PvO₂ 35–45 mmHg

When to Use VBG Instead of ABG

Evaluating acid-base status when oxygenation data is not critical (e.g., DKA, COPD exacerbation).
Monitoring pH and CO₂ trends over time in stable patients.
When arterial access is difficult or contraindicated.

When ABG is Preferred

Assessing oxygenation or ventilation in critically ill patients.
Evaluating response to oxygen therapy or mechanical ventilation.
Diagnosing severe acid-base disturbances or hypoxemia.

Quick Reference

Venous and arterial values correlate closely for pH and HCO₃⁻ but differ significantly in oxygenation. Always use ABG for accurate PaO₂ and SaO₂ interpretation.

Related Resources

Last updated: October 2025