To evaluate whether elevated pulmonary vascular permeability is associated with extravascular water accumulation and lack of response to surfactant replacement therapy in newborn Respiratory Distress Syndrome(RDS),we measured the pulmonary transcapillary escape rate(PTCER)for gallium-68 labelled transferrin and the extravascular density(EVD)with the quantitative, non-invasive nuclear medicine imaging technique of positron emission tomography(PET).Three groups of infants were studied: 1)NORMAL:infants without respiratory symptoms;2)RDS-NO SURF:preterm infants with RDS who did not require surfactant replacement;3)RDS-SURF:preterm infants with RDS who required surfactant.The NORMAL infants underwent one PET scan within the first 8 days of life.All but one RDS infant underwent 2 PET scans at least 6 hours apart within the first 24 hrs of life.The RDS-SURF infants underwent scans before and 6-8 hours after surfactant administration.The mean PTCER and EVD for all infants with RDS(131±48 10-4/min and 33±6 gms/100ml lung respectively) were significantly greater than for NORMAL infants(78±27 10-4/min and 28±6 gms/100ml lung respectively,p=0.02 and 0.04 respectively;Table).There was a correlation between PTCER and EVD(p=0.02,r=0.48).Initial PTCER and EVD were not significantly different between the two RDS subgroups and did not change between the two scans.The oxygen index (OI) decreased by 47% in the RDS_SURF subgroup.We conclude: 1)infants with RDS have increased pulmonary vascular permeability and extravascular water accumulation in the lungs;2)response to surfactant replacement therapy is independent of changes in the PTCER or EVD.

Table 1
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