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 SpO ₂ differs from the end-6MWT SpO ₂ in patients with chronic respiratory disease. A total of 86 subjects underwent the 6MWT according to a standardized protocol with continuous monitoring of SpO ₂ by pulse oximeter. Comparison of nadir SpO ₂ and end SpO ₂ 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 SpO ₂ 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 SpO ₂ was slightly lower than end-test SpO ₂ (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 SpO ₂ and end SpO ₂ (p = 0.04). End SpO ₂ 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 SpO ₂ and the nadir SpO ₂ are similar during the 6MWT. However, the end SpO ₂ does not give an accurate estimate of nadir SpO ₂ in patients who rest. Consideration should be given to the constant monitoring of SpO ₂ during the 6MWT.