Chronic respiratory failure is a slower process, the body has a chance to compensate for the imbalance of arterial gases (the kidneys are responsible for this). Some people
with COPD (emphysema, chronic bronchitis etc) have high
CO2 in their blood, but it seems to be their norm. If they have low O2 levels as well, then they are treated with oxygen. Prognosis is tough to guess at because people can live with low O2/high CO2 levels for some time if it is chronic.