FIGURE 1.

Study flowchart. Inclusion period was from 29 February 2020 to 31 August 2021. Propensity score (PS) matching was performed with the following variables: sex, age, respiratory rate at hospital admission, arterial oxygen tension/inspiratory oxygen fraction at hospital admission (categorised as >300, 200– ≤300, 100– ≤200 or ≤100 mmHg), time from hospital admission to intensive care unit (ICU) admission (categorised as ≤2 or >2 days), immunodepression, corticosteroid treatment and COVID-19 wave. ETI: endotracheal intubation; IMV: invasive mechanical ventilation.