Assessment of Six-Minute Walk Test Among Discharge-Ready Severe COVID-19 Patients: A Cross-Sectional Study

Background Among patients hospitalized for severe pneumonia due to coronavirus disease (COVID-19), clinical stability and normal resting peripheral oxygen saturation (SpO(2)) levels are widely used as a discharge criterion after recovery. It is unknown whether a test to assess the functional exercise capacity, like a six-minute walk test (6MWT), can add to the appropriateness of discharge criteria. Methods A cross-sectional study was conducted at a tertiary care COVID-19 hospital in India from 01(st) to 31(st) May 2021. All patients considered fit for discharge after recovery from "severe" COVID-19 pneumonia were subjected to 6MWT. Fitness for discharge was assessed by clinical stability and resting SpO(2) above 93% for three consecutive days. Patients were considered to have failed the 6MWT if there was ≥4% fall in SpO(2) or if they could not complete the test. Serum samples were analyzed for levels of C-reactive protein (CRP), interleukin-6 (IL-6), and lactate dehydrogenase (LDH) at the time of discharge. Results Fifty-three discharge-ready patients with a mean age of 54.54 ± 14.35 years with a male preponderance (60.38%) were analyzed. Thirty-three (62.26%) patients failed the 6MWT with a median six-minute walk distance (6MWD) of 270 m (60-360). A total of 45 (84.91%) patients had a fall in SpO(2) during the test. The median change in SpO(2) (∆SpO(2)) was 5% ranging from -6% to 8%. Serum LDH was significantly higher among patients who failed the 6MWT with a median LDH of 334 IU/L (38.96-2339) versus 261 IU/L (49.2-494) (p = 0.02). The difference was not significant for CRP or IL-6. There was no statistically significant correlation between the inflammatory markers with either 6MWD or (∆SpO(2)). Conclusion Two-thirds of the patients considered fit for discharge after recovery from severe COVID-19 pneumonia failed 6MWT, implying reduced functional exercise capacity and exertional hypoxia. Serum LDH levels were higher in these patients but not in other inflammatory markers. None of the inflammatory markers at discharge correlated with 6MWD or ∆SpO(2) of 6MWT.