Prediction of exercise-induced desaturation in COPD patients without resting hypoxemia: a retrospective study

Background: There is no universally accepted criterion for assessing exercise-induced desaturation (EID). The purpose of this study is to compare the two methods regularly used methods for determining EID in COPD patients,as well as to explore the risk factors and predictors related to EID. Methods: The 6MWT was performed with continuous SpO 2 monitoring on patients with stable COPD. Using two methods (method A: "SpO 2rest -SpO 2min ≥ 4% and/or SpO 2min < 90%", method B: "SpO 2rest -SpO 2end ≥ 4% and/or SpO 2end < 90%") as EID determination criteria to assess the incidence of EID. The differences and consistency of the two methods are compared. Moreover, we collected data through the pulmonary function test, mMRC dyspnea score, COPD assessment test, BODE index and CT-defined emphysema. Univariate and multivariate logistic regression analyses were used to identify factors affecting the EID. For the parameters that predict EID in 6MWT, a receiver operating characteristic (ROC) curve analysis was employed. Results: The analysis included 124 patients. The overall incidence of EID was 62.1% by using method A as the criterion and 51.6% by method B. All of the EID patients found by method B were included in the EID patients identified by method A, as well as 13 new-EID patients. The difference in diagnostic outcomes between the two approaches was not statistically significant ( P >0.05), but they were in excellent agreement (Kappa=0.807, P =0.001). Logistic regression analyses found that D L CO SB% pred, D L CO/VA% pred, CAT score, mean density, PD15, emphysema volume and %LAA were significant determinants of the EID. For predicting EID, the ROC analysis produced AUC and cutoffs of 0.689 and 50.45% (D L CO SB% pred), 0.707 and 75.0% (D L CO/VA% pred), 0.727 and 15 points (CAT score), 0.691 and -955.00HU (PD15), 0.671 and -856.46HU (mean density), 0.668 and 338.14ml (emphysema volume) and 0.656 and 7.63% (%LAA), respectively. Conclusions: Two methods evaluating EID in this research are in a good agreement, method A can find more EID patients by focusing on SpO 2min. When conditions are constrained, it is also sufficient to assess EID in COPD patients by method B. In terms of the predictors of EID, D L CO SB% pred, D L CO/VA% pred, CAT score and CT-defined emphysema are all statistically significant test variables to determine EID.