ACIDEMIA ENHANCES THE INHIBITORY EFFECT OF HYPOXIA ON FETAL LUNG LIQUID SECRETION IN SHEEP

Previous studies have shown that moderate fetal asphyxia reduces the s ecretion rate of fetal lung liquid. The present aim was to determine t he relative effects of the individual components of asphyxia (hypoxia, hypercapnia and acidaemia) on lung liquid secretion in fetal sheep. F etal hyperoxia was also studied to determine the extent to which lung liquid secretion is restricted by the relatively low fetal blood PO2. As each manipulation of fetal blood gas tensions and pH treatment prod uced alterations in more than one aspect of blood composition, data fr om all treatment groups were combined and a multiple analysis of varia nce was performed to determine the separate effects of PaO2, PaCO2, Sa O(2) and pHa. Lung liquid secretion rate was significantly reduced whe n mean PaO2 values were below 24.5 mmHg (range 12.9-24.3 mmHg). When P aO2 values below 24.5 mmHg occurred in combination with pHa values bel ow 7.275 (range 6.934-7.268) the secretion rates were further reduced. Alterations in pHa alone or in PaCO2 had no significant effect. These results indicate that hypoxia is the principal factor responsible for the inhibition of lung liquid secretion during asphyxia and that acid aemia enhances this inhibition.