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Baseline oxygen saturation predicts exercise desaturation below prescription threshold in patients with chronic
M T Knower1, D P Dunagan, N E Adair
1Section on Pulmonary and Critical Care, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157-1054, USA. mknower@wfubmc.edu
Background:
Recent studies of exercise-induced hypoxemia in patients with chronic obstructive pulmonary disease (COPD) have shown that oxygen supplementation during exertion increases exercise tolerance and alleviates dyspnea. Although measurements of forced expiratory volume in 1 second and diffusion capacity for carbon monoxide (DLCO) are known to predict exercise-induced 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 70% or less who underwent exercise testing for desaturation. Any desaturation to 88% or less with exercise was considered significant. Nineteen patients with total lung capacity of 80% or less were excluded to avoid evaluating those with combined obstructive and restrictive defects; 81 patients remained available for study.
Results:
Nineteen (51%) of 37 patients with resting saturation of 95% or less desaturated with exercise as opposed to 7 (16%) of 44 with resting saturation of 96% or greater (P =.001). The sensitivity and the negative predictive value of baseline saturation of 95% or less as a screening test for exercise 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 desaturation 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 merits further study in larger prospective patient cohorts.