896 The effect of maternal hyper-oxygenation on vascular resistance of growth restricted fetuses

Abstract

To study the effects of maternal hyper-oxygenation on fetal circulation as measured by Doppler ultrasonography in the growth restricted fetus. This is prospective observational study. Patients were positioned in low-fowlers position with the head of the bed elevated between 15 and 30 degrees for approximately 15 minutes. 100% oxygen was delivered at a flow rate of 8 l/min through a close-fitting facemask (with a reservoir and non-rebreathing valve) for a duration of 10 minutes. Fetal doppler ultrasonography was performed 20 minutes prior and after administration of supplemental oxygen. Doppler values for umbilical artery, middle cerebral artery, ductus venosus, were obtained during a period of fetal apnea, preferably fetal quiet sleep as flow waveforms and cardiac output have been shown to vary with behavioral states. At least three consecutive waveforms were gathered. Six patients with growth restricted fetuses were enrolled. We found no statistically signficant differences in umbilical artery peak systolic flow, end diastolic flow, resistance index, pulsatility index. or systolic to diastolic ratio before and after maternal hyper-oxygenation. We also found no difference in middle cerebral artery peak systolic flow, end diastolic flow, resistance index, and pulsatility index before and after maternal hyper-oxygenation. We were unable to measure fetal ductus venosus doppler flow due to hyperactivity of the fetus within the 20 minutes following maternal oxygen administration. Maternal hyper-oxygenation caused a noted increase in fetal movements in the growth restricted fetus, and precluded aquisition of fetal ductus venosus assessement following oxygen administration. We found no significant differences in umbilical artery and middle cerebral artery doppler flow measurements following maternal hyper-oxygenation.