pCO2

Carbon dioxide molecule.

The pCO₂, PCO₂, $p_{{\ce {CO2}}}$or $P_{{\ce {CO2}}}$ is the partial pressure of carbon dioxide (CO₂), often used in reference to blood but also used in oceanography to describe the partial pressure of CO₂ in the ocean and in life support systems engineering and underwater diving to describe the partial pressure in a breathing gas. Usually, the arterial blood is the relevant context; the symbol for $P_{{\ce {CO2}}}$ in arterial blood is $P_{a_{{\ce {CO2}}}}$. Measurement of $P_{a_{{\ce {CO2}}}}$ in the systemic circulation indicates the effectiveness of ventilation at the lungs' alveoli, given the diffusing capacity of the gas. It is a good indicator of respiratory function and the closely related factor of acid–base homeostasis, reflecting the amount of acid in the blood (without lactic acid).

Values in blood

• Its normal values are in the range 35–45 mmHg.
• If the $P_{{\ce {CO2}}}$ is less than 35 mmHg, the patient is hyperventilating, and if the pH (potential hydrogen) is greater than 7.45, corresponding to a respiratory alkalosis.
• If the $P_{{\ce {CO2}}}$ is higher than 45 mmHg, the patient is hypoventilating, and if the pH is less than 7.35, is in respiratory acidosis.

See also

• Acidosis
• Alkalosis
• Arterial blood gas
• Blood gas tension
• Chemical equilibrium
• Hypercapnia
• pH
• pKa