What are the normal partial pressure of oxygen (PO2) and partial pressure of carbon dioxide (PCO2) values in a venous blood gas (VBG)?

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Last updated: October 13, 2026 • View editorial policy

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Normal VBG Values

For venous blood gas (VBG) analysis in adults, the normal PO2 range is approximately 19-65 mmHg (or 16-74 mmHg in some populations), and the normal PCO2 range is 38-58 mmHg for females and slightly higher for males (up to 62 mmHg). 1, 2

Understanding VBG vs ABG Reference Ranges

The provided guidelines focus primarily on arterial blood gas (ABG) values, where normal PaCO2 is 4.6-6.1 kPa (34-46 mmHg) 3. However, venous values differ systematically from arterial values due to tissue oxygen extraction and CO2 production.

Specific VBG Normal Values

PCO2 (Partial Pressure of Carbon Dioxide)

  • Female: 33.2-58.7 mmHg (Chinese population) 2
  • Male: 32.8-62.2 mmHg (Chinese population) 2
  • General adult: 38-58 mmHg (Western population) 1

The venous PCO2 is typically 4-5 mmHg higher than arterial PCO2 due to CO2 production in tissues 1.

PO2 (Partial Pressure of Oxygen)

  • 19-65 mmHg (Western population) 1
  • 16-74 mmHg (Chinese population) 2

Critical caveat: Venous PO2 has wide variability and poor correlation with arterial PO2 1, 4. This makes venous PO2 unreliable for assessing oxygenation status. Always use pulse oximetry (SpO2) or arterial sampling when oxygenation assessment is clinically important 5.

Additional VBG Parameters

  • pH: 7.30-7.43 (or 7.282-7.438) 1, 2
  • Bicarbonate: 22-30 mmol/L 1
  • Base excess: -1.9 to 4.5 mmol/L 1

The venous pH is approximately 0.03-0.04 units lower than arterial pH 1, 4.

Clinical Application Pitfalls

Major limitation: While VBG can reliably assess pH and PCO2 in stable patients and those with mild-to-moderate acid-base disturbances, the method becomes unreliable in severe metabolic acidemia (arterial pH <7.10) 4. In one case, a patient with arterial pH 7.07 had calculated pH of 7.42 using venous-to-arterial conversion—a dangerous discrepancy 4.

When VBG is insufficient:

  • Suspected severe acidemia or alkalemia
  • Need for precise oxygenation assessment (PaO2)
  • Respiratory failure requiring ventilator adjustments
  • Any situation where arterial PO2 specifically guides therapy 5

In over one-third of ED patients with respiratory complaints, ABG results changed management decisions based initially on VBG, most commonly regarding oxygen therapy adjustments 5.

References

1
Research

Reference intervals for venous blood gas measurement in adults.

Clinical chemistry and laboratory medicine, 2021

2
Research

Reference intervals for venous blood gas measurement in a healthy Chinese population.

Clinica chimica acta; international journal of clinical chemistry, 2027

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.