Partial Pressure of Carbon Dioxide (pCO2), Blood

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Subject: Partial Pressure of Carbon Dioxide (pCO2), Blood

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Definition

  • pCO2 is a measure of tension or pressure of carbon dioxide dissolved in the blood. The pCO2 of blood represents the balance between cellular production of CO2 and ventilatory removal of CO2. A normal, steady pCO2 indicates that the lungs are removing CO2 at about same rate as tissues producing CO2. A change on pCO2 indicates an alteration in this balance, usually due to the change in ventilatory status.

  • Normal range:

    • Arterial: 35–45 mm Hg

    • Venous: 41–51 mm Hg

Interpretation

Increased In

  • Acute respiratory acidosis

    • Depression of respiratory center

    • Suppressed neuromuscular system

    • Pulmonary disorders

    • Inadequate mechanical ventilation

  • Chronic respiratory acidosis

    • Decreased alveolar ventilation

    • Hypoventilation

  • Compensation in metabolic alkalosis

Decreased In

  • Respiratory alkalosis

    • Increased stimulation of respiratory center

    • Hypermetabolic states

    • Mechanical hyperventilation

  • Compensation in metabolic acidosis

Limitations

  • Respiratory conditions will primarily affect pCO2, whereas metabolic disturbances are first reflected in the HCO3.

  • Values are slightly lower in supine position.

  • Difference between arterial blood and venous blood varies considerably, depending on the skin temperature, length of stasis, and muscular activity.

 
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