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VBG to ABG Converter
Venous Blood Gas (VBG) analysis is less invasive and safer to perform than arterial sampling. In many clinical scenarios (e.g., Diabetic Ketoacidosis, COPD exacerbations), a VBG can accurately predict acid-base status.
This tool applies standard physiological offsets to VBG results to estimate the corresponding Arterial Blood Gas (ABG) values. Note: VBG cannot accurately estimate arterial oxygenation (pO2).
Venous Values (Input)
VBGmmHg
mEq/L
Estimated Arterial
Note: VBG correlates well with ABG for pH and pCO₂, but poorly for pO₂.
Logic & Evidence
Physiological Differences: As blood passes through tissues, it releases O₂ and picks up CO₂ and metabolic byproducts. Therefore, venous blood is slightly more acidic and has a higher pCO₂ than arterial blood.
Conversion Factors:
• pH: Arterial pH ≈ Venous pH + 0.035.
• pCO₂: Arterial pCO₂ ≈ Venous pCO₂ − 4 to 5 mmHg. (This calculator subtracts 5).
• HCO₃⁻: Venous and Arterial bicarbonate values are roughly equivalent (difference ≈ 1 mEq/L).
Clinical References
How to Use This Converter
Follow these steps to estimate ABG values.
Obtain VBG
Draw a peripheral venous blood gas sample.
Enter Values
Input the venous pH and pCO₂. Input HCO₃⁻ if available (it acts as a pass-through).
Interpret
Use the estimated values for Acid-Base interpretation. If oxygenation status is a concern, an actual ABG or Pulse Oximetry is required.
Frequently Asked Questions
Yes. If the venous pCO₂ is less than 45 mmHg, arterial hypercapnia is extremely unlikely. If VBG pCO₂ is high, it correlates well with ABG pCO₂ but may be slightly higher.
If precise pO₂ measurement is needed (hypoxia), or if the patient is in severe shock (where the venous-arterial difference widens significantly).