We have analysed the predictors of survival in patients starting long-term domiciliary oxygen therapy (LTO) for chronic hypoxia caused by parenchymal lung disease. In 240 patients (136 males) LTO was started at a mean age of 70 yrs. Survivors have been followed up for a minimum of 28 months (range 28-57 months). Interstitial fibrosis was the sole cause of hypoxia in 51 patients, and late sequelae of pulmonary tuberculosis in 48 patients. More than one (mixed) disease caused hypoxia in 124 patients. Patients with tuberculosis (TB) started LTO with significantly higher values of arterial carbon dioxide tension (PaCO2) and markedly lower spirometry volumes than patients with interstitial fibrosis. In the total patient group survival was correlated in the univariate analysis to cause(s) of hypoxia, performance status and PaCO2 when breathing air. TB had a relatively good prognosis, whilst interstitial fibrosis implied a poor long-term survival. A PaCO2 of below 5.5 kPa and a poor performance class was associated with increased mortality rates. In TB patients, survival was better when thoracic deformity contributed to hypoxia. In patients with interstitial fibrosis, a forced vital capacity of below 2.1 l was associated with increased mortality. Concomitant chronic obstructive pulmonary disease was associated with better survival than interstitial fibrosis alone. In the multivariate analysis, survival was found correlated to performance status, presence or absence of thoracic deformity and forced expiratory volume in one second (FEV1) and forced vital capacity (FVC). A high FEV1 and a low FVC were associated with increased mortality rates. After consideration of spirometry values, cause(s) of hypoxia, apart from thoracic deformity, was not significantly associated with survival. The reason for the increased mortality rate in patient developing chronic hypoxia at high FEV1 levels could be more advanced diffusion impairment or ventilation-perfusion mismatch in patients developing chronic hypoxia at less advanced stages of obstruction.
