In terms of blood gas measures studied, only arterial carbon dioxide tension (PaCO 2 ) showed a statistically significant increase with increasing exacerbation severity (p < 0.017) ( Figure 4A ) as well as out-versus in-patients (p < 0.05) ( Figure 4B ). In the case of oxygen saturation, it gradually decreased with increasing exacerbation severity with statistically significant differences between Levels I and II (p < 0.001) as well as Levels I and III (p = 0.011) ( Figure  4C ). It also decreased going from an out-patient to an inpatient setting (P < 0.001) ( Figure 4D ).