What does a peripheral venous blood gas with PO2 (partial pressure of oxygen) 24 mmHg, PCO2 (partial pressure of carbon dioxide) 38 mmHg, HCO3 (bicarbonate) 23.4 mmol/L, O2 saturation (oxygen saturation) 43 % and pH 7.39 indicate?

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Last updated: November 8, 2026 • View editorial policy

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Interpretation of Peripheral Venous Blood Gas Results

These peripheral venous blood gas values are essentially normal and indicate adequate tissue perfusion and oxygenation with no evidence of respiratory or metabolic disturbance.

Analysis of the Values

Your venous blood gas shows:

  • pH 7.39: Normal (venous reference range 7.30-7.43) 1
  • PCO2 38 mmHg: Normal (venous reference range 38-58 mmHg) 1
  • HCO3 23.4 mmol/L: Normal (venous reference range 22-30 mmol/L) 1
  • Venous O2 saturation 43%: Normal (venous reference range 23-93%) 1
  • PO2 24 mmHg: Normal (venous reference range 19-65 mmHg) 1

Key Clinical Context

The low PO2 (24 mmHg) and oxygen saturation (43%) in this venous sample are physiologically normal and expected. These values reflect oxygen extraction by tissues - blood returns to the heart with lower oxygen content after delivering oxygen to peripheral tissues 2. This is fundamentally different from arterial blood, where low values would indicate hypoxemia requiring urgent intervention.

Important Distinctions Between Venous and Arterial Values

Research demonstrates that venous PO2 is typically 36.9 mmHg lower than arterial PO2, with arterial values ranging from 27.2 to 46.6 mmHg higher 3. The venous oxygen saturation of 43% suggests:

  • Normal tissue oxygen extraction
  • Adequate cardiac output
  • No evidence of tissue hypoxia or shock

If this patient had tissue hypoxia from inadequate oxygen delivery (as in sepsis, low cardiac output, or severe hypoxemia), you would expect metabolic acidosis with elevated lactate and low bicarbonate 2.

Clinical Implications

No intervention is required based on these values alone. The normal pH and PCO2 indicate:

  • No respiratory acidosis or alkalosis
  • No metabolic acidosis or alkalosis
  • No hypercapnic respiratory failure

When to Obtain Arterial Blood Gas

You should obtain an arterial blood gas if 2:

  • The patient has clinical signs of hypoxemia (tachypnea, tachycardia, confusion, cyanosis)
  • Oxygen saturation by pulse oximetry is <94% (or <88% if at risk for hypercapnic respiratory failure)
  • The patient is critically ill or in shock
  • You need to assess true arterial oxygenation status

Common Pitfall to Avoid

Do not misinterpret normal venous oxygen values as indicating arterial hypoxemia. The most critical error would be initiating oxygen therapy or escalating care based solely on these normal venous values. Venous blood gas cannot reliably assess arterial oxygenation - the PO2 values differ too significantly to be clinically interchangeable 3, 4.

Summary Assessment

This venous blood gas demonstrates normal acid-base balance, normal ventilation (PCO2), and normal tissue oxygen extraction. The patient requires clinical correlation with pulse oximetry and physical examination, but these venous values themselves indicate physiologic stability.

References

1
Research

Reference intervals for venous blood gas measurement in adults.

Clinical chemistry and laboratory medicine, 2021

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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.