Constant high CO2
One of the reasons that a physician might avoid giving her o2 is that it may stop her breathing.
Our main way to control breathing is through sensing of co2
. If a person has had a constantly high level of co2 over times due to any respiratory disease, then their body sees that level as normal. Sudden drop in that co2 level can lead to not breathing at all. Please consult your pcp for more info.
Answer assisted by Saurabh Bajpai, Medical Student