Bacterial Lysates on Respiratory Tract Microecology and Evaluation of the Efficacy of Prevention and Treatment of VAP

Inclusion Criteria: * Patients admitted to ICU for mechanical ventilation * The expected mechanical ventilation time is more than 72h * Sign the informed consent form when conscious and voluntary, and complete the questionnaire survey and follow-up as required; If it is unable to sign the informed consent form and complete the questionnaire survey and follow-up, the legal representative or guardian can act on behalf of it. Exclusion Criteria: * Ventilator associated pneumonia is known and confirmed * Pregnant or lactating female * Allergic to the active ingredients of bacterial lysates or any excipients listed in the ingredients * Patients with autoimmune diseases * Patients with acute intestinal infection * Patients participating in other clinical studies at the same time * Patients considered unsuitable by other researchers to participate in this study