Using SpO2 Recovery Index after a 6-Minute Walk Test to Predict Respiratory-Related Events in Hospitalized Patients with Interstitial Pneumonia

Abstract

Although the prognostic factors of interstitial pneumonia (IP) patients have been reported, IP has poor prognosis. Hospitalized patients with IP have severely impaired pulmonary diffusion capacity and prominent desaturation. We hypothesized that determining oxygen saturation recovery (SpO₂ recovery index) after the 6-minute walk test (6MWT) can provide additional prognostic information regarding rehospitalization for respiratory-related events. We evaluated 73 IP patients at our hospital for demographic characteristics, pulmonary function tests and 6MWT. The Kaplan-Meier method was used to estimate rehospitalisation for respiratory-related events using SpO₂ recovery index. Cox regression analysis revealed a relationship between SpO₂ recovery index and rehospitalisation. The optimum cutoff value of SpO₂ recovery index was 4% (sensitivity, 71.4%; specificity, 79.2%). SpO₂ recovery index was most closely related to pulmonary diffusion capacity (r = 0.684, P < 0.001). In a multivariable model, it was the strongest independent predictor of rehospitalisation for respiratory-related events (hazard ratio, 0.3; 95% confidence interval, 0.10-0.90; P = 0.032). In this study, we estimated pulmonary diffusion capacity using SpO₂ recovery index values obtained from 6MWT. A SpO₂ recovery index of <4% can be useful in predicting rehospitalisation for respiratory-related events.