Baseline oxygen saturation predicts exercise desaturation below prescription threshold in patients with chronic obstructive pulmonary disease

Background: Recent studies of exercise-induced hypoxemia in patients with c hronic obstructive pulmonary disease (COPD) have shown that oxygen suppleme ntation during exertion increases exercise tolerance and alleviates dyspnea . Although measurements of forced expiratory volume in 1 second and diffusi on capacity for carl;on monoxide (DLCO) are known to predict exercise-induc ed desaturation in patients with COPD, baseline oxygen saturation has never been studied as a predictor of exercise-induced desaturation. Methods: A retrospective analysis was performed of 100 consecutive patients with forced expiratory volume in 1 second-forced vital capacity ratio of 7 0% or less who underwent exercise testing for desaturation. Any desaturatio n to 88% or less with exercise was considered significant. Nineteen patient s with total lung capacity of 80% or less were excluded to avoid evaluating those with combined obstructive and restrictive defects; 81 patients remai ned available for study. Results: Nineteen (51%) of 37 patients with resting saturation of 95% or le ss desaturated with exercise as opposed to 7 (16%) of 44 with resting satur ation of 96% or greater (P=.001). The sensitivity and the negative predicti ve value of baseline saturation of 95% or less as a screening test for exer cise desaturation were 73% and 84%, respectively. If all patients with DLCO of 36% or less were excluded, 40 patients were left for study. Eight (40%) of 20 patients with baseline saturation of 95% or less compared with 0 of 20 with resting saturation of 96% or greater desaturated with exercise (P=. 006). In this subset, the sensitivity and the negative predictive value of baseline saturation of 95% or less as a screening test for exercise desatur ation both improved to 100%. Conclusions: In patients with COPD, baseline saturation of 95% or less is a good screening test for exercise desaturation, especially in patients with DLCO greater than 36%. This readily available office screening procedure m erits further study in larger prospective patient cohorts.