CO transfer capacity as a determining factor of survival for severe hypoxaemic COPD patients under long-term oxygen therapy.

The transfer capacity for carbon monoxide is a commonly used method in clinical practice but is rarely considered as a prognostic factor for patients under long term oxygen therapy (LTOT). LTOT was applied to 217 stable, severely hypoxaemic (arterial oxygen tension (PaO2 less than 7.3 kPa or 55 mmHg) chronic obstructive pulmonary disease (COPD) patients, according to the usual recommendations. The average survival rate of this series is rather poor: 46% at 24 months. There is nevertheless an important difference between patients with a normal transfer coefficient and those with a decreased one (79% survival at 2 yrs as compared to 37%). On the other hand, the degree of airflow limitation has no prognostic value in the present series of very disabled patients. We can conclude that hypoxaemic COPD patients with a severely decreased transfer coefficient have a poor prognosis, even under LTOT, compared to patients with an equivalent impairment of airflow limitation and hypoxaemia but with a normal CO transfer factor/alveolar ventilation ratio (TLCO/VA).