The goal of this observational study is to learn about the effect of steroid therapy in patients with COVID-19 ARDS. The main questions it aims to answer are:

• Differences between patients with COVID-19 ARDS before and after steroid treatment in BALF single cell landscape, as well as patients with different prognosis.
• Differences between COVID-19 and non COVID-19 ARDS patients in BALF single cell landscape.

Participants will Choose whether to use or not to utilize steroid treatment based on conditions.

Collect BALF from COVID-19 and non-COVID-19 ARDS patients both before and during remission, then perform single-cell sequencing.

Inclusion Criteria:

• Severe ARDS patients

Exclusion Criteria:

• None

4 COVID-19 ARDS patients, 4 non-COVID-19 ARDS patients