The effect of maternal oxygenation on cardiopulmonary haemodynamics during the transition at birth in preterm lambs.

Abstract

Objectives: The cardiovascular transition at birth is a potential period of instability for preterm infants. The influence of alterations to the fetal partial pressure of oxygen (PaO2) on the cardiovascular stability are not well understood. We hypothesized that increasing maternal, and subsequently, fetal oxygenation will increase fetal pulmonary blood flow and reduce cardiovascular instability during the transition at birth. Method(s): Preterm sheep fetuses (0.9 gestation) were exteriorised by caesarean section and instrumented for measurement of carotid arterial pressure and flow, pulmonary blood flow (PBF), cerebral (SctO2) and arterial (SaO2) oxygenation. Ewes were randomised to either maternal oxygen supplementation (O2Supp) to achieve fetal PaO2 > 20 mmHg (n = 7) or maternal oxygen reduction (O2Red) to achieve a fetal PaO2 < 20 mmHg (n = 8). Once target fetal PaO2 were obtained, lambs underwent immediate cord clamping, with respiratory support withheld for 1 min, and then maintained for 30-min. Physiological variables were recorded continuously throughout the study. Result(s): Maternal oxygen supplementation resulted in significantly higher pH, PaO2, SpO2 and SctO2 compared to O2Red and increased PBF (28.5 +/- 7.8 vs 4.0 +/- 3.2mL/min/kg) which was maintained throughout the 1 min period between cord clamping and ventilation onset. Cord clamping resulted in an increase in blood pressure in O2Supp lambs and a rapid fall in fetal oxygenation. Ventilation onset resulted in a rapid increase in carotid blood pressure and flow in O2Red lambs which was mitigated by prior maternal oxygen supplementation. Conclusion(s): Maternal oxygen supplementation increases fetal oxygenation and PBF prior to umbilical cord clamping and prevented rapid fluctuations in carotid blood pressure and flow, which may provide improved cardiovascular stability in preterm infants.