Study cohort derived from ECMO cases recorded in the ELSO database between 1986 and 2006. A total of 21,218 neonatal pulmonary ECMO cases were identified after ECMO runs initiated for cardiac conditions and post cardiac surgeries were excluded. Inclusion criteria was GA >= 34 weeks and <43 weeks. Exclusion criteria included infants with major congenital disorders including congenital diaphragmatic hernias, cardiac defects, chromosomal/genetic abnormalities, missing GA, mismatched GA and birth weight.