Nonrespiratory causes of death becoming more common in oxygen-dependent COPD

Mortality rates due to nonrespiratory causes have increased over time in patients receiving long-term oxygen therapy for chronic obstructive pulmonary disease (COPD), according to a recent study.

Swedish researchers performed a prospective study of 7,628 patients with COPD (4,027 women, 3,601 men) who started long-term oxygen therapy between Jan. 1, 1987 and Dec. 31, 2004. Patients were followed until the end of the study, until oxygen therapy was stopped, or until death. The goal of the study was to determine whether mortality rates and causes of death have changed as more older people and more women with severe COPD have begun receiving long-term oxygen therapy. The study's primary end point was cause of death according to the Swedish National Causes of Death Register. The study results were published online Jan. 7 by the American Journal of Respiratory and Critical Care Medicine.

Median follow-up was 1.7 years (range, 0 to 18 years). Overall, 5,457 patients (71.5%) died during the study, with a 1.6% (95% CI, 0.9% to 2.2%; P<0.001) annual increase in crude overall mortality rate. Seventy-one percent of deaths were due to respiratory causes, 16% were due to circulatory causes, 7.6% were due to cancer and 1.1% were due to digestive organ disease. The absolute risk for death increased by 2.8% annually (95% CI, 1.3% to 4.3%; P<0.001) for circulatory disease and by 7.8% (95% CI, 1.9% to 14.0%; P=0.009) for digestive organ disease but decreased by 2.7% annually (95% CI, 2.0% to 3.3%; P<0.001) for respiratory disease and by 3.4% (95% CI, 1.1% to 5.7%; P=0.004) for lung cancer.

The authors cautioned that their mortality estimates are based on death certificate data and that estimates of cause-specific mortality could have been affected by changes in such factors as diagnostics and coding. However, they concluded that both overall mortality rates and mortality rates due to nonrespiratory causes have increased over time in patients with oxygen-dependent COPD. "The present study supports the important prognostic role of co-morbidity in oxygen-dependent COPD and shows that mortality has increased for non-respiratory causes, such as cardiovascular disease," the authors wrote.