carbon dioxide

newbie here...first timer. been wearing a cpap four years and suddenly tonight i have an unanswered question....where does the carbon dioxide go if not back into the lungs? is it diluted w/ the incoming oxygen to the degree that it isn't harmful? is there a dr. in the house? any answers out there folks? thanks to all.

Your "circuit" has a vent doesn't it? They are usually the exhaust ports on the mask. There is always air flowing through your circuit. The CO2 you are breathing out in mixed in with the air that is coming into the mask from your cpap and is "flushed" out with that air.