Changes in lung liquid dynamics induced by prolonged fetal hypoxemia

Our aim was to determine the effect of prolonged fetal hypoxemia, induced by reduced maternal uterine blood flow (RUBF), on fetal lung liquid secretion, flow, and volume. In chronically catheterized fetal sheep, lung liquid volume (V(L)) and the secretion rate of lung liquid (V̇(S)) were measured before and after a 24-h period of either RUBF or normoxemia. Tracheal fluid flow and the incidence of fetal breathing movements (FBM) were measured before, during, and after the 24-h period. In normoxic control fetuses V̇(S) was not significantly altered. After 24 h of RUBF, V̇(S) was significantly (P < 0.005) reduced compared with pre-RUBF values. During 24 h of RUBF the incidence of FBM declined initially but returned to control values after 12-16 h. In seven of eight fetuses, over the 12- to 24-h period of RUBF, large amounts of liquid (22.7-62.6 ml) were drawn into the lungs during FBM, resulting in a net movement of amniotic fluid into the lungs. During the 18- to 24-h period or RUBF, changes in the incidence of FBM were found to be significantly and positively correlated (r = 0.86, P < 0.005) with the changes in V(L) that occurred over the 24-h period. Thus, prolonged RUBF can result in the inhalation of large volumes of amniotic fluid by the fetus, which could be a cause of in utero meconium aspiration.