Inclusion Criteria:  Gestational age <32w; Admit within 72 hours of birth; The guardian signs the informed consent; OI (oxygenation index >300)  Exclusion Criteria:  Newborns with severe congenital malformations or various chromosomal diseases, genetic metabolic diseases, severe neurological diseases; Newborns who die during the study; Newborns who drop out of the study; Newborns who have NEC during hospitalization