Inspired fraction of carbon dioxide in oxygen supply to chronic pulmonary disease

Summary Hypoxemic patients with chronic obstructive pulmonary disease (COPD) are at risk of carbon dioxide (CO 2 ) retention during oxygen therapy and hypercapnia in COPD is associated with an ominous prognosis. Rebreathing with oxygen mask is possible in practice and possibly affects CO 2 retention due to an increased inspired fraction of CO 2 . Its effects on arterial partial pressure of CO 2 during oxygen supply have, to the best of our knowledge, never been studied. We measured the inspired fraction of CO 2 in eighteen non-hypoxemic stable COPD patients with a capnograph during a 5min trial with two different modes of oxygen supply (oxygen mask without reservoir bag and nasal prongs, respectively at a flow of 10l/min and 2l/min). We found no significant increase in inspiratory CO 2 concentration. These findings suggest that inspired fraction of CO 2 does not increase markedly during controlled oxygen therapy.