Predicting walking-induced oxygen desaturations in COPD patients: a statistical model.

BACKGROUND Oxygen desaturation during walking can have important consequence on prognosis of COPD patients. However, a standard 6-min walk test (6MWT), useful in detecting desaturation in COPD patients, can be difficult to execute in some settings of COPD management, as in the community healthcare service. We evaluated a new scoring system for the risk of oxygen desaturation during walking in COPD patients: the walking desaturation score. METHODS We collected data from symptomatic COPD in-patients admitted for rehabilitation (derivation cohort) and out-patients referred to the local community health service (validation cohort). S(pO2) was monitored during 6MWT, and the subjects were classified as walking desaturators or non-desaturators. By a regression analysis model we assigned a weighted score proportional to the measured percentage of explained variance for each variable. Risk estimates were computed as odds ratios. A receiver operating characteristic curve analysis and a Hosmer-Lemeshow goodness-of-fit test were then performed to measure discrimination and calibration of walking desaturation score. RESULTS Baseline characteristics in the derivation cohort (n = 435, 74% of whom were walking desaturators) and the validation cohort (n = 238, 37% of whom were walking desaturators) were different. Resting arterial oxygen saturation measured from an arterial blood sample, P(aO2), and percent-of-predicted FEV1 were the variables that predicted walking desaturation. The proportion of walking desaturators (and odds ratio estimate) gradually increased according to walking desaturation score (range 0-6) and associated categories of desaturation risk (total walking desaturation score: low 0 or 1, high 2-3, very high 4-6) (chi-square P < .001). There was considerable predictive discrimination (area under the curve 0.90, 95% CI 0.86-0.93, P < .001), and calibration (Hosmer-Lemeshow chi-square 1.31, P = .86) values have been shown. CONCLUSIONS Walking desaturation score accurately predicts and classifies the risk of walking desaturation in COPD patients. ClinicalTrials.gov Number NCT01303913.