433 Maternal hyperoxia and its effect on the ductus venosus

Abstract

The ductus venosus(DV) Doppler waveform is a valuable tool in the assessment of any fetal condition that may affect forward cardiac function. We sought to investigate the effects of maternal hyperoxygenation(MH) on the DV Doppler in the third trimester. Forty-six women with a singleton pregnancy ≥31 weeks’ gestational age(GA) were prospectively recruited.The DV Doppler was obtained at the isthmus, near its origin from the umbilical vein in a mid-sagittal view. A Doppler assessment of the umbilical artery (UA) was also performed. Doppler measurements were taken at baseline and following MH for 10minutes.Measurements of mean systolic, diastolic and ‘a’ wave velocities as well as pulsatility index for veins (PIV), preload index (PLI) and peak velocity index for veins (PVIV) ratios were obtained. Satisfactory DV Doppler recordings were obtained from 59% of participants.Qualitative assessment of the DV waveform confirmed a positive ‘a’ wave in all fetuses. DV mean systolic, diastolic and ‘a’ wave velocities increased following MH.The DV Doppler ratios including PIV, PLI and PVIV did not change in response to MH (Table 1).There were no changes in the resistance of the UA in response to MH. The DV responds to MH. Due to the increase in systole,diastole, and atrial contraction contemporaneously, the ratios between these elements were unchanged. As gestation advances the PIV and a-wave-related ratios decrease owing to a decrease in utero-placental resistance and an increase in cardiac compliance and contractility. We have demonstrated no change in the utero-placental resistance indices, therefore the most likely explanation is a constriction of the DV, suggesting that the DV is responsive to alterations in oxygen tension in the fetal blood.The decrease in the DV calibre in response to MH infers that the size of the DV is directly responsible for the shunting of umbilical venous blood away from the hepatic circulation.These findings warrant further investigation in relation to the effect of MH on myocardial function particularly in the context of congenital cardiac disease.