Age, sex, length of ICU stay, history of SLE, renal biopsy pathology, organ damage (including skin, serositis, arthritis, heart, kidney, blood, central nervous and other system damage) and type and dose of immunosuppressants in the 2 months before ICU admission were recorded. Laboratory indicators included CRP, TLC, CD3 + , CD4 + , CD8 + , CD20 + lymphocyte count, albumin, globulin, procalcitonin (PCT), interleukin-6 (IL-6), hemoglobin (Hgb), platelet (PLT), N-terminal B-type natriuretic peptide (NT-proBNP), serum creatinine (Scr), blood urea nitrogen (BUN), complement C3, complement C4, antinuclear antibody (ANA), anti–double-stranded DNA antibody (anti-dsDNA), anticardiolipin antibody (ACL), lupus anticoagulant factor (LA), and proteinuria. The SLE Disease Activity Index (SLE-DAI) and Acute Physiology and Chronic Health Assessment (APACHE) II scores were calculated. The diagnosis of pulmonary infection and severe pulmonary infection was based on diagnostic criteria developed by the Infectious Diseases Society of America/American Thoracic Society (IDSA/ATS) [11 (link)]. Sepsis was defined according to the diagnostic criteria Sepsis 3.0 [12 (link)]. ARDS was defined according to the Berlin diagnostic criteria [13 (link)].