Outcomes
The primary outcome of the study was a composite of all-cause death or invasive mechanical ventilation, whereas the secondary outcomes were in hospital all-cause mortality and the requirement for invasive mechanical ventilation. The mortality rates in patients with COVID-19 depend largely on the need to start oxygen supply and the level of respiratory support [14]. Therefore, patients were divided into two groups according to oxygen saturation and the requirement for oxygen supply at enrolment, that is, with oxygen saturation at rest ≤93% (group 1) and >93% (group 2). The study outcomes were evaluated separately in the two groups. Primary and secondary end-points, if met, were determined prospectively for treated patients and retrospectively by chart review for control patients.