Abstract
BACKGROUND: Chronic respiratory failure may occur as a consequence of chronic obstructive pulmonary disease (COPD) and is associated with significant morbidity and mortality. Hypoxemia is determined by underlying disease characteristics and comorbidities. Severe hypoxemia is typically only found in subjects with severe airflow obstruction (FEV(1)<50% predicted). However, how hypoxemia relates to disease characteristics is not fully understood. METHODS: In the French Initiatives BPCO real-life cohort, arterial blood gases were routinely collected in most patients. Relationships between severe hypoxemia, defined by a Pa0(2)<60 mmHg (8 kPa) and clinical/lung function features, comorbidities and mortality were assessed. In subjects with severe hypoxemia, clinical characteristics and comorbidities were compared between those with non-severe versus severe airflow limitation. Classification and regression trees (CART) were used to define clinically relevant subgroups (phenotypes). RESULTS: Arterial blood gases were available from 887 subjects, of which 146 (16%) exhibited severe hypoxemia. Compared to subjects with a PaO2≥60 mmHg, the severe hypoxemia group exhibited higher mMRC dyspnea score, lower FEV(1), higher RV and RV/TLC, more impaired quality of life, lower 6-minute walking distance, less frequent history of asthma, more frequent diabetes and higher 3-year mortality rate (14% versus 8%, p=0.026). Compared to subjects with Pa0(2)<60 mmHg and FEV(1)<50% (n=115, 13%), those with severe hypoxemia but FEV1≥50% predicted (n=31) were older, had higher BMI, less hyperinflation, better quality of life and a higher rate of diabetes (29% versus 13%, p=0.02). Severe hypoxemia was better related to CART-defined phenotypes than to GOLD ABCD classification. CONCLUSION: In this cohort of stable COPD subjects, severe hypoxemia was associated with worse prognosis and more severe symptoms, airflow limitation and hyperinflation. Compared to subjects with severe hypoxemia and severe airflow limitation, subjects with severe hypoxemia despite non-severe airflow limitation were older, had higher BMI and more diagnosed diabetes. TRIAL REGISTRATION: 04-479.