1. Main objectives: ① To determine the optimal timing for bronchoscopic lung lavage in treating severe pneumonia in children, providing evidence-based guidance for the standardized clinical implementation of this technique. ② To establish a multidimensional efficacy evaluation system encompassing clinical symptoms, blood gas analysis, and inflammatory markers.
2. Secondary objectives: ① To assess the impact of different intervention timings on clinical outcomes, including the time to temperature normalization, resolution of lung rales, length of hospital stay, hospitalization costs, and mortality rate. ② To evaluate the therapeutic effects at the pathophysiological level by measuring inflammatory factors (e.g., IL-6, IL-8), epithelial/endothelial injury biomarkers (e.g., SP-D, angiopoietin-2), and indicators of pathogen clearance, thereby clarifying the treatment's effects on inflammation control, lung injury repair, and pathogen elimination. ③ To enhance the accumulation of safety data by calculating the incidence of adverse events related to bronchoscopic procedures (such as airway bleeding and hypoxemia) and further defining the safety profile of this technique in the pediatric population.