[3] The subscript x in each symbol represents the source of the gas being measured: "a" meaning arterial, "A" being alveolar, "v" being venous, and "c" being capillary.
[6][7] Carbon dioxide is a by-product of food metabolism and in high amounts has toxic effects including: dyspnea, acidosis and altered consciousness.
[8] PaCO2 – Partial pressure of carbon dioxide at sea level in arterial blood is between 35 and 45 mmHg (4.7 and 6.0 kPa).
[9] PaCO – Partial pressure of CO at sea level in arterial blood is approximately 0.02 mmHg (0.00267 kPa).
[10] When used alongside the pH balance of the blood, the PaCO2 and HCO−3 (and lactate) suggest to the health care practitioner which interventions, if any, should be made.