Oxygen desaturation during a 4-minute step test: predicting survival in idiopathic pulmonary fibrosis

PaO2 during exertion is a significant predictor of IPF survival. The aim of study was to assess oxygen desaturation for predicting survival in IPF patients at the end of a 4-minute step test.

A longitudinal study was done in 59 patients with IPF from February 1998 to January 2005. Upon initial examination, lung function testing was performed, as were 4-minute step tests, in which patients stepped up and down on a 20-cm single step at a self-paced rate. In the final minute, oxygen saturation by pulse oximetry (SpO2) was measured.

Median survival was 58 months. SpO2 at rest and during stepping, dyspnea score, as well as FVC% and DLCO% were found to be significant predictors of mortality. Desaturation to 89% or less,correlated with a hazard ratio of 2.39 for IPF mortality (95% CI, 1.16-3.63; p < 0.0001). In patients with such desaturation, four-year survival was 39%, compared to 96% in those with no desaturation. In a multivariate Cox analysis, only SpO2 during stepping remained significant (p < 0.0001). A DLco < 45% of predicted (n=40 patients) correlated with a hazard ratio of 2.23 for mortality (95% CI, 0.73-3.71; p < 0.0001). When the analysis was repeated including DLco, SpO2 and DLco remained significant (p < 0.05).

Desaturation to 89% or less in a 4-min step test is a strong predictor of mortality in IPF patients.