Effects of acute oligohydramnios on respiratory system of fetal sheep.

Prolonged oligohydramnios, or a lack of amniotic fluid, is associated with pulmonary hypoplasia and subsequent perinatal morbidity, but it is unclear whether short-term or acute oligohydramnios has any effect on the fetal respiratory system. To investigate the acute effects of removal of amniotic fluid, we studied nine chronically catheterized fetal sheep at 122-127 days gestation. During a control period, we measured the volume of fluid in the fetal potential airways and air spaces (VL), production rate of that fluid, incidence and amplitude of fetal breathing movements, tracheal pressures, and fetal plasma concentrations of cortisol, epinephrine, and norepinephrine. We then drained the amniotic fluid for a short period of time [24-48 h, 30.0 +/- 4.0 (SE) h] and repeated the above measurements. The volume of fluid drained for the initial studies was 1,004 +/- 236 ml. Acute oligohydramnios decreased VL from 35.4 +/- 2.9 ml/kg during control to 22.0 +/- 1.6 after oligohydramnios (P less than 0.004). Acute oligohydramnios did not affect the fetal lung fluid production rate, fetal breathing movements, or any of the other measured variables. Seven repeat studies were performed in six of the fetuses after reaccumulation of the amniotic fluid at 130-138 days, and in four of these studies the lung volume also decreased, although the overall mean for the repeat studies was not significantly different (27.0 +/- 5.2 ml/kg for control vs. 25.5 +/- 5.5 ml/kg for oligohydramnios). Again, none of the other measured variables were altered by oligohydramnios in the repeat studies.(ABSTRACT TRUNCATED AT 250 WORDS)