Normal Ranges

CO2 is regulated by the lungs. A normal PaCO2 level is 35 to 45 millimeters of mercury. CO2 is a powerful stimulant of respiration. The lungs will increase the respiratory rate, causing hyperventilation, when the blood is too acidic. It does this to excrete more CO2 and decrease the acidity of the bloodstream. If the blood is too alkalotic, the lungs will decrease the respiratory rate causing hypoventilation. It does this to retain more CO2 and increase the acidity of the bloodstream.