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38. Early stages of hyaline membrane disease

In 78 preterm infants with HMD, the initial PaO2 values, in 100% O2 (hyperoxya test), were lower than expected for age in the first 4 hr of life, then dropped and stayed low for 24 to 72 hr and started to rise. It was also shown that the shorter the gestational age, the earlier the rise and the limit seems to be at 33 weeks gestation. The drop in PaO2 could be explained by intra-pulmonary shunt through increased atelectatic areas or by extra-pulmonary shunting (fetal shunts).The functional resiual capaciy (FRC), was measured by the close circuit belium dilution method, as an index of pulmonary aeration, in six preterm babies with HMD and was found to be 50% lower than expected value, already before the 4th hr of life, and remained low without any significant change for the first 24 hr. Thus, it can be speculated that the drop in PaO2 is due to extrapulmonary shunting through the foramen ovale and ductus and arteriosus and not to an increase in atelectasis.