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.
Department of Medical and Surgical Sciences, University of Modena and Reggio Emilia, Modena, Italy. ecrisafulli@pneumonet.it
Ernesto
E
Crisafulli
Andrea
A
Iattoni
Elena
E
Venturelli
Gherardo
G
Siscaro
Claudio
C
Beneventi
Alfredo
A
Cesario
Enrico M
EM
Clini
D000368:Aged; D000369:Aged, 80 and over; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D010092:Oximetry; D010100:Oxygen / Q000097:blood*; D011379:Prognosis; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000097:blood* / Q000503:physiopathology*; D012372:ROC Curve; D012044:Regression Analysis; D018570:Risk Assessment; D013147:Spirometry; D016138:Walking / Q000502:physiology*
D010100:Oxygen
6-min walk test; COPD; community healthcare; decision making; oxygen desaturation; risk score