Fig. 20:  This Figure shows data from the National Emphysema Treatment Trial (NETT), which was a prospective randomized control trial that compared lung volume reduction surgery to optimized medical treatment in patients with severe emphysema and a PaO₂ >60 mmHg and employing different intensities of supplemental oxygen therapy.

In a post hoc analysis of the group who received optimized medical treatment for 3 years, Drummond et al^[12] looked at the survival probability of patients with a PaO₂ > 60 mmHg who used supplemental oxygen continuously, intermittently, or no oxygen at all.  It can be seen that the group who did not use oxygen at all (stippled line) had a better survival than that group who used oxygen intermittently (dashed line), suggesting that perhaps that either the patients who use supplemental oxygen had greater symptoms and were sicker, or that supplemental oxygen, itself, could have a detrimental effect on that patient group.  However the investigators at that were unable to discern whether patients who use oxygen continuously with a PaO₂ >60 mmHg are a more symptomatic group (perhaps from comorbid conditions, etc. or other, unmeasurable factors), or that perhaps oxygen could be having a detrimental effect.