THE FETAL LUNG PROFILE: BEYOND THE L/S RATIO

Abstract

Progressive expiratory atelectasis of RDS is attributed to deficient surfactant phospholipids. Fetal lung biosynthesis of the principal ones, lecithin (phosphatidyl choline, PC) the most abundant, and phosphatidyl inositol (PI) and phosphatidyl glycerol (PG), the acidic phospholipids, are determined developmentally during gestation. They appear in amniotic fluid and are used to monitor maturity of fetal lung and optimal time for delivery by means of a LUNG PROFILE, utilizing 2-dimensional thin layer chromatography of the extracted amniotic fluid lipids, comparing on a gestational scale L/S ratio, % disaturated PC, % PI and % PG with level of maturity. The leclthin/sphingomyelin (L/S) ratio relates concentrations of PC to sphingomyelin acting as an “internal standard”. With lung maturation PC increases and there is increasing disaturation of its fatty acid esters, measured as acetone precipitable fraction of PC. PI and PG are essential to the stability of PC; PI increases parallel to PC to 35-36 weeks, then declines. At 36-37 weeks, PG appears and increases; by term and in mature surfactant it is the 2d most abundant surfactant phospholipid. RDS is never seen once PG is present. On recovery from RDS increasing PI is seen; PG may not appear until near 36 gest wks. In infants with retained lung fluid, PG is not present in amniotic fluid but appears after birth in tracheal secretions as symptoms disappear. The lung profile greatly enhances both accuracy of prediction and understanding of lung development and eliminates non-diagnostic intermediate values.