The flu morped into COPD last Friday. I called my pulmonologist on Monday only to be told he couldn't return my call until Thursday!!! I've never heard of such a thing. Called my primary. He prescribed prednisone tapering dose. Today (Wednesday) is day #2. My O2 sat runs between 93 and 97 on 2 L basal cannula. How long b4 the prednisone kicks in???