# pCO2

The pCO2, PCO2, ${\displaystyle p_{{\ce {CO2}}}}$or ${\displaystyle P_{{\ce {CO2}}}}$ 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 ${\displaystyle P_{{\ce {CO2}}}}$ in arterial blood is ${\displaystyle P_{a_{{\ce {CO2}}}}}$. Measurement of ${\displaystyle P_{a_{{\ce {CO2}}}}}$ 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).
• If the ${\displaystyle P_{{\ce {CO2}}}}$ 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 ${\displaystyle P_{{\ce {CO2}}}}$ is higher than 45 mmHg, the patient is hypoventilating, and if the pH is less than 7.35, is in respiratory acidosis.[1][2]