VAP（Ventilator-associated pneumonia）is the most common complication of mechanical ventilation in severely ill patients. VAP is defined as pneumonia occurring 48 hours after patients receive mechanical ventilation, including pneumonia occurring within 48 hours after extubation. It is one of the important causes of hospital-acquired infection, and the incidence of VAP in children on mechanical ventilation is about 10%, or 7/1000 days of mechanical ventilation, and the overall mortality is 10-24%.Research has so far explained the relationship between bacteria isolated from human biological samples and VAP pathogens. Most studies are limited to the level of bacterial species, and there are few reports on bacterial genotyping, and there is a lack of scientific basis for the pathogenesis of VAP caused by bacteria in ventilator pipeline. The aim of the study is to investigate pathogen of the sputum in deep respiratory tract of patients with mechanical ventilation in PICU by the means of second generation sequencing (NGS).

Children receiving invasive mechanical ventilation in the intensive care unit (PICU) of the Pediatric Hospital of Fudan University will be included. Deep sputum samples were collected within 24 h and on day 5 of mechanical ventilation, respectively, and sent for NGS at the same time. Sputum etiology examination is performed with sputum culture blood free DNA test.

The basic clinical data of the children (age, sex, weight, PICU diagnosis and other basic information, as well as the time of start and end of invasive mechanical ventilation for basic diseases, Glasgow coma score (GCS score), 3rd generation pediatric mortality risk score III(Prism III score), CRP, PCT, white blood cell count and body temperature will be recorded。 Clinical data related to the use of glucocorticoids, antibiotics and other drugs as well as life support such as renal replacement therapy, extracorporeal membrane, lung oxygenation and other life support were collected. Time and method of diagnosis of VAP pathogens were collected.

By comparing sensitivity and specificity of NGS and conventional sputum specimens for detection of VAP, the clinical value of mNGS in VAP will be studied.

Inclusion Criteria:

• The time of invasive mechanical ventilation was less than 24 h when admitted to PICU Total duration of invasive mechanical ventilation is over 5 days

Exclusion Criteria:

• Participants in other clinical trials in the same period No Informed Consent signed

Children receiving invasive mechanical ventilation in PICU