Patients receiving TTOz therapy showed a significant reduction in the P(A-a)02 at the end of six months and the P(A-a)Oa was reduced (mean —10.4 mm Hg) in all patients who demonstrated an increase in Pa02 above 55 mm Hg while breathing ambient air. All patients who demonstrated an increase in Pa02 to levels above 55 mm Hg continued to experience arterial oxygen desaturation while walking. This may represent an important risk factor for progression of pulmonary hypertension and an increase in P(A-a)02 if oxygen therapy is terminated. Hypoxemia during sleep also may be a risk factor but this was not evaluated in this study.
This report supports the recommendation of the recent oxygen consensus conference that recertification for LTOT in patients who are clinically unstable when oxygen therapy is begun should be done within three months and that an increase in Pa02 after three months may reflect the beneficial therapeutic effects of oxygen therapy rather than fluctuations in clinical stability. Discontinuation of oxygen therapy based on a single ABG measurement performed after three months of therapy cannot be medically justified. Further research into the mechanisms by which oxygen therapy promotes a reduction in P(A-a)02 and results in an increased Pa02 in some patients is still needed.