Influence of prenatal adrenaline infusion on arterial blood gases after Caesarean delivery in the lamb

The efficacy of pulmonary gas exchange immediately after delivery is inversely related to the volume of liquid in the lung at birth, but aspiration of as much liquid as possible from the lung before Caesarean delivery fails to improve postnatal oxygenation ( P a,O 2 ) to the level achieved after spontaneous term delivery. We hypothesised that the differing respiratory benefit of aspiration and vaginal delivery results from the differing volume of lung liquid remaining after aspiration (17 ml (kg body weight) −1 ) and labour (7 ml kg −1 ). We addressed this hypothesis by reducing lung liquid volume to an estimated 7 ml kg −1 by infusing adrenaline to seven fetal lambs at 140 days gestation (term is 147 days) before performing Caesarean delivery and obtaining postnatal blood gases for comparison with samples from lambs delivered vaginally. Infusion of adrenaline to fetuses caused a progressive decline in arterial O 2 saturation ( S a,O 2 ), pH and base excess, but no change in arterial partial pressure of O 2 ( P a,O 2 ) or CO 2 ( P a,CO 2 ). After birth, P a,O 2 rapidly rose to the same level in adrenaline-treated and vaginal-delivery groups. A severe acidosis occurred in the adrenaline-treated group and this appeared to be related to a higher P a,CO 2 and a transiently lower S a,O 2 in this group. We conclude that adrenaline infusion can enhance postnatal P a,O 2 levels in the newborn lamb, but this beneficial effect may be outweighed by the severe acidosis that develops after prolonged prenatal adrenaline treatment.