Silent Hypoxia in Patients with SARS CoV-2 Infection before Hospital Discharge

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

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

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

Conclusion: The 6 MWT 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.

Keywords: COVID-19; discharge; dyspnoea; exercise test; hypoxia.