The PCO2 is the partial pressure of carbon dioxide (CO2), normally used in reference to blood, but also used in Oceanography to describe the partial pressure of CO2 in the Ocean. Usually the arterial blood is the relevant context; the symbol for PCO2 in arterial blood is PaCO2. Measurement of PaCO2 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).
- Its normal values are in the range 35–45 mmHg.
- If the PCO2 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 PCO2 is higher than 45 mmHg, the patient is hypoventilating, and if the pH is less than 7.35, is in respiratory acidosis.