Are there some out there that can be in a closed loop? I assume there must be since that's what an anesthesiologist would use, but would probably cost way more than I am willing.
If you have an O2 deficiency for some reason, I think more aeration rather than more O2 in the air used for aeration is easier to achieve and doesn't risk hyper oxygenation, which may have drawbacks.
I'm not sure what effect the device has on CO2. I could not easily find the answer.