Patients were divided into 2 groups: In control group bacterial cultures were carried out in bronchial fluid and patients treated as usual; and in the intervertional group multiplex real-time PCR were further performed to identify 5 common pathogenic bacteria: Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, Staphylococus aureus and initial antibiotic administration based on multiplex real-time PCR results.