In patients with idiopathic pulmonary arterial hypertension (iPAH) current guidelines recommend a long-term oxygen supply for patients with an arterial blood O2 partial pressure < 60 mmHg or < 91% of arterial O2 saturation. However, the prognostic impact in iPAH patients receiving best standard of care (i.e. PAH targeted medications) is unknown.
Retrospective we analyzed iPAH patients entered into the Giessen Pulmonary Hypertension Registry between January 2000 and April 2017 with either documented absence of oxygen therapy or documented use until end of follow up. In addition, only patients with lung function testing at time of enrolment were included. The primary outcome was 5 years overall survival obtained from the registry, end of follow up was July 2017. The prognostic relevance of oxygen therapy was assessed by Kaplan–Meier analyses stratified for disease severity (PVR or CO dichotomized at the median).
In total 198 iPAH patients were included (median PVR 878 [IQR 1265 – 592] dyn; cardiac output 3.9 [IQR 4.7-3.1] l/min, pO2 69 [IQR 61-77] mmHg, DLCO 60 [IQR 72-46] % pred., age 59 [IQR 72-46] years) of which 119 were receiving long-term oxygen therapy. Patients receiving no oxygen supply showed a superior overall 5 year survival when stratified by preserved cardiac output (91.1%) or lower PVR (85.2%). Of note, the subgroup of patients with preserved hemodynamics and oxygen therapy showed an overall 5 year survival almost comparable to patients with impaired pulmonary hemodynamics (with and without oxygen therapy) (stratified by cardiac output (48.6 % vs 66.4% vs 61.3%); stratified by PVR (54.4% vs 70.0% vs 51.6%) (overall log-rank p < 0.001). This subgroup of patients with preserved hemodynamics and oxygen therapy was presenting with a severely impaired DLCO and lowest pO2 in comparison (p< 0.05 across all groups, One-Way-Anova).
Not surprisingly iPAH patients without oxygen therapy and preserved pulmonary hemodynamics showed the best overall survival. However, the subgroup of iPAH patients with preserved pulmonary hemodynamics and oxygen therapy
showed an impaired overall survival almost comparable to patients with advanced disease. Moreover, these data indicate that patients requiring O2-therapy who per se seem to have an impaired outcome might resemble the proposed pulmonary phenotype with reduced DLCO. Taking into account the retrospective database analysis, our preliminary data indicate that oxygen therapy might not be able to influence the clinical course of patients with advanced disease or with the so called “pulmonary phenotype of iPAH”.