Should oxyhaemoglobin saturation be monitored continuously during the 6-minute walk test?

Guidelines for conducting the 6-minute walk test (6MWT) indicate that oxyhaemoglobin saturation (SpO 2) should not be monitored constantly during the test. The aim of this study was to determine whether the nadir SpO2 differs from the end-6MWT SpO2 in patients with chronic respiratory disease. A total of 86 subjects underwent the 6MWT according to a standardized protocol with continuous monitoring of SpO2 by pulse oximeter. Comparison of nadir SpO2 and end SpO2 was made and the proportion of subjects with important desaturation according to each measure was determined. The effect of resting during the 6MWT on the likelihood of a significant difference between nadir and end SpO2 was evaluated. A total of 29 subjects with chronic obstructive pulmonary disease (COPD; mean [SD] forced expiratory volume in 1 second [FEV1] 51[21] % predicted) and 57 with interstitial lung disease (ILD; TLCO 49[18] % predicted) were studied. Nadir SpO2 was slightly lower than end-test SpO2 (median 87% vs. 88%, p < 0.001) with differences ranging from 1% to 10%. Those who rested during the test (n = 14) were more likely to have a significant difference between nadir SpO2 and end SpO2 (p = 0.04). End SpO2 did not accurately identify desaturation in 21% of subjects. No differences between COPD and ILD were observed. For most patients with chronic respiratory disease, the end SpO2 and the nadir SpO 2 are similar during the 6MWT. However, the end SpO2 does not give an accurate estimate of nadir SpO2 in patients who rest. Consideration should be given to the constant monitoring of SpO2 during the 6MWT.