Prediction of mortality in patients with cystic fibrosis

The majority of patients with cystic fibrosis die in early adulthood of lung disease. Lung transplantation is a treatment option for patients with advanced pulmonary disease, although the waiting period for organs may be as long as two years. Our purpose was to determine whether the risk of death due to respiratory failure could be predicted one or two years in advance on the basis of pulmonary function, blood gas levels, and nutritional status.

The study cohort consisted of 673 patients followed between 1977 and 1989. In each patient, pulmonary function, blood gas levels, nutritional status, and vital status were assessed between 1977 and 1987. Cox proportional-hazards regression analysis was used to compute the relative risk of death within one or two years after particular measurements. The effects of age and sex on mortality were also included in the analysis.

One hundred ninety patients (28 percent) died during the study period. Overall, patients with a forced expiratory volume in one second (FEV1) less than 30 percent of the predicted value, a partial pressure of arterial oxygen below 55 mm Hg, or a partial pressure of arterial carbon dioxide above 50 mm Hg had two-year mortality rates above 50 percent. Among the laboratory measurements, the FEV1 was the most significant predictor of mortality, but age and sex were also significant in predicting risk. After adjustment for age and sex, the relative risk of death within two years was 2.0 (95 percent confidence interval, 1.9 to 2.2) for each decrement in the FEV1 of 10 percent below the predicted value. Among patients with the same FEV1, the relative risk of death was 2.0 (95 percent confidence interval, 1.5 to 2.6) in patients 10 years younger than other patients, and 2.2 (1.6 to 3.1) in female patients as compared with male patients.

Patients with cystic fibrosis should be considered candidates for lung transplantation when the FEV1 falls below 30 percent of the predicted value. Female patients and younger patients may need to be considered for transplantation at an earlier stage.