I've been reading here about CO2 retention, and I understand that pretty well. But for a long time now, both my O2 and CO2 levels are low. At the same time? I don't understand at all. I'm transitioning to a new pulmonologist and haven't seen mine in months, so I haven't been able to ask this question. I forgot to ask my PCP. How can both be low? It has been like this both in the hospital with acute respiratory failure and almost all of the rest of the time. Is this normal with COPD?