Search

We exposed 128- to 130-day-gestation fetal lambs by cesarean section leaving the umbilical cord and placenta undisturbed, and we then treated the lungs with pulmonary conditioning (i.e., repeated prolonged inflations to 35 cm H2O, followed by a continuous positive airway pressure of 15 cm H2O). To investigate the added effect of pulmonary vasodilation upon the increase of total compliance and pulmonary oxygen uptake, we also administered acetylcholine intravenously at a rate of 80 μg min-1. Eleven of 13 lambs met the endpoint criteria of either compliance (0.5 ml [cm H2O]––1 kg––1; 1 animal), or pulmonary oxygen uptake (6 ml kg––1 min––1; 6 animals), or both (4 animals), and were delivered within 0.6 ± 0.3 h. This time was significantly (p < 0.05) shorter than previously seen in similar studies without the infusion of a vasodilator; all animals so delivered survived 24 h of mechanical ventilation in excellent health. We suggest that pharmacologic pulmonary vasodilation, in addition to deep sustained pulmonary insufflation and distension, is an effective and rapid means of transforming stiff immature lungs into lungs that can sustain normal ventilation and gas exchange.

Breathing during fetal life is periodic, it is inhibited by maternal/fetal hypoxia and it is stimulated by maternal/fetal hypercapnia. We use ECMO to study the influence of direct changes in blood gases or temperature on the fetus in 8 sheep at 125-130 days of gestation. For ECMO a 12 F silastic catheter (drainage, external jugular) and a 9.6 F catheter (return, carotid artery) were placed. Total blood flow varied between 60-80 ml/kg/min. After connection the fetuses were maintained normocapnic and hyperoxic (PaO2 63 ± 8 mmHg in carotid or axillary artery) for 8 to 19 hours to observe changes in breathing incidence or sleep cycling. Fetal PaCO2 was varied in 3 fetuses during fetal hyperoxia or normoxia. Fetal temperature was varied by decreasing blood temperature of the system (2 fetuses). 2 Fetuses were kept hyperoxic during maternal hypoxia. Preliminary observations: a) During fetal hyperoxia the fetuses continued to cycle between high and low voltage and fetal breathing showed in some cases a decrease in incidence, but overall it did not change significantly, b) During fetal hypercapnia (4-8 mmHg), fetal breathing was stimulated and it seemed to bear a relationship with oxygenation, c) During fetal hypothermia fetal breathing was stimulated, d) Fetal breathing was stopped when the ewe was made hypoxic and the fetus was kept hyperoxic, this suggests that during maternal/placental hypoxia a substance is produced which has a direct action on fetal breathing. ECMO proved to be a possible technique to study fetal physiology.