Silent hypoxia in patients with SARS CoV-2 infection before hospital discharge

Objective: To assess the degree of hypoxia and subjective dyspnea elicited by a 6-minute walking test (6MWT) in COVID-19 patients prior to discharge.

Methods: A 6MWT was performed in 26 discharge-ready COVID-19 patients without chronic pulmonary disease or cardiac failure. Heart rate, oxyhemoglobin saturation (SpO₂), respiratory rate, and subjective dyspnea measured on the Borg CR-10 scale were measured before and immediately after the 6MWT, with continuous monitoring of SpO₂ and heart rate during the 6MWT. The 6MWT was terminated if SpO₂ dropped below 90%. A historical cohort of 204 patients with idiopathic pulmonary fibrosis (IPF) was used for comparison.

Results: 13 (50%) of the COVID-19 patients developed exercise-induced hypoxia (SpO₂ < 90%) during the 6MWT, of which one third had pulmonary embolism. COVID-19 patients experienced less hypoxia-related dyspnea during the 6MWT compared with patients with IPF.

Conclusion: The 6MWT is a potential tool in the diagnosis of asymptomatic exercise-induced hypoxia in hospitalized COVID-19 patients prior to discharge. Due to important methodological limitations, further studies are needed to confirm our findings and to investigate their clinical consequences.