Early Inflammatory-Immune Stratification and Precision Glucocorticoid Intervention in Acute Respiratory Failure Induced by Community-Acquired Pneumonia

Inclusion Criteria:1. Age ≥ 18 years. 2. Admitted to the Intensive Care Unit (ICU) within 48 hours. 3. Meet diagnostic criteria for bacterial community-acquired pneumonia (CAP). 4. Meet at least one severity criterion: a) Receiving mechanical ventilation for acute respiratory failure with PEEP ≥ 5 cmH2O; OR b) On high-flow oxygen with FiO2 ≥ 0.5 and PaO2/FiO2 ratio ≤ 250 mmHg; OR c) On a reservoir oxygen mask with PaO2 below the specified flow threshold (see protocol). 5. Signed informed consent. \- Exclusion Criteria: 1. Suspected aspiration pneumonia. 2. Invasive mechanical ventilation within 14 days prior to admission. 3. Diagnosis of hospital-acquired or ventilator-associated pneumonia (HAP/VAP). 4. Positive for influenza virus, active tuberculosis, or fungal infection (except Pneumocystis jirovecii). 5. Active viral hepatitis or herpesvirus infection. 6. Hypersensitivity to glucocorticoids, or contraindications as judged by the investigator (e.g., severe concurrent infections, active gastrointestinal hemorrhage). 7. High-dose glucocorticoid therapy (\>1 mg/kg/day prednisone equivalent) within 30 days for underlying disease. 8. Death within 24 hours of ICU admission. 9. Pregnancy or lactation. 10. Participation in other interventional studies or refusal to participate. \-