244: The effect of maternal hyperoxygenation on fetal pulmonary vasoreactivity and on blood flow patterns in the umbilical artery and middle cerebral artery in pregnancy

Abstract

We sought to evaluate the changes in fetal pulmonary artery, umbilical artery and middle cerebral artery Doppler waveforms in response to maternal hyperoxygenation. Nineteen pregnant women with a singleton gestation in the third trimester were prospectively recruited to the study. The protocol for the investigation was approved by the National Ethics Committee and the Health Products Regulatory Authority (HPRA) in Ireland. Informed consent was signed by all participants. Blood flow velocity waveforms were recorded during periods of fetal quiescence. A comprehensive fetal echocardiogram was performed on all subjects. Pulsatility index (PI), acceleration time (AT), and ejection time (ET) were taken within the proximal portion of the fetal main pulmonary artery (PA). AT:ET was used to assess pulmonary vascular resistance (PVR). The sample volume gate was adjusted to 3 mm, and the angle of insonation was maintained at ≤ 15°. Umbilical artery (UAD) and middle cerebral artery (MCA) PIs were also obtained. Measurements were taken at baseline and repeated immediately following maternal hyperoxygenation with 60% FiO2 for a 10-minute duration. Values are presented as medians [Inter-quartile ranges] or means ±SD. The median gestational age was 36 [33 - 37] weeks. There was a decrease in fetal PA PI following maternal hyperoxygenation (from 2.47 [2.11 - 2.80] to 2.08 [1.75 - 2.49], p=0.02) with a mean decrease of 21% [9-36] from the baseline. There was an increase in PA AT (43 [40-47] to 57 [47 - 60] ms, p=0.005) leading to an increase in AT:ET (indicating a fall in PVR) following maternal hyperoxygenation (0.25 [0.24 - 0.28] to 0.32 [0.26 - 0.34], p=0.005). There were no changes in the PIs of the UAD or MCA following hyperoxygenation (0.93 to 0.99, p=0.92 and 1.54 to 1.72, p=0.20 respectively). This study demonstrates that maternal hyperoxygenation diminishes the relative vasoconstriction in the fetal pulmonary vasculature. There were no significant changes to the MCA or UAD PI indices following hyperoxygenation suggesting that this effect is unique to the fetal pulmonary vessels.