Doppler ultrasound evaluation of ductus venosus blood flow during acute hypoxemia in fetal lambs

Abstract

It has been demonstrated with invasive techniques in fetal lambs that the ratio of ductus venosus to umbilical vein blood flow rate (DV/UV ratio) increases during hypoxemia and infusion of catecholamines. Recently it was found in human fetuses using pulsed wave Doppler ultrasound equipment that the DV/UV ratio in fetuses with intrauterine growth restriction was significantly increased. The aim of the present study was to show in fetal lambs whether routine Doppler ultrasound devices were capable of determining the DV/UV ratio with sufficient reliability. The experiments were performed on seven near-term instrumented fetal lambs using pulsed wave Doppler ultrasound to measure flow rates (derived, in milliliters per min, from the intensity-weighted mean velocity (Vmean) and the vessel's cross-sectional area) in the ductus venosus and intra-abdominal umbilical vein. Fetal hypoxemia was induced by administering a low-oxygen gas to the ewe (5-7% oxygen, 2% carbon dioxide). Fetal arterial pO2 and heart rate decreased significantly during maternal hypoxia. The proportion of umbilical venous return passing through the ductus venous in controls was 36 +/- 5% (mean +/- SD). This increased to 53 +/- 6% (p < 0.001) because the umbilical venous blood flow fell during late hypoxemia when the heart rate had decreased by 20%. Severe hypoxemia tended to reduce the mean velocity (Vmean) and the minimum velocity (Vmin) (based on the maximum velocity envelope curve) in the ductus venosus, descending aorta and inferior vena cava. The pulsatility index of the umbilical artery significantly increased at the end of hypoxemia. We conclude that determination of the proportion of umbilical vein blood flow entering the ductus venosus by Doppler ultrasound in a clinical setting may contribute to the detection and evaluation of fetal distress.

Ductus venosus velocimetry in acute fetal acidemia and impending fetal death in a sheep model of increased placental vascular resistance

“…Our finding is in agreement with published experimental studies (13,22). It has been shown that a comparable degree of fetal hypoxemia with our study caused a profound and immediate distension of the DV inlet (14,22).…”

Doppler ultrasonographic evaluation of ductus venosus blood flow in 55 canine fetuses

“…The morphological evaluation and velocimetry of the DV during pregnancy has been described in humans and sheep [4,5,7]. Our study describes the DV in canine fetus and its main flow characteristics recorded using non-invasive Doppler sonography.…”

“…In this way oxygen can distribute preferentially to the fetal cardiac tissue and brain [4]. It was postulated that, during fetal hypoxia, over the 70 % of blood flow passing through the umbilical vein can shunt in the DV [5].…”

“…Fetal lambs have been used as animal model to study DV in humans [4,5]. In humans, Doppler evaluation of DV is believed to be a relevant indicator of fetal well being [8,9].…”

Original paper. Do Umbilical Cord Wrapped Around the Fetal Body Can Mimic Signs of Aortal Coarctation?

“…20 The problems with umbilical cord encompass its knots and many morphological abnormalities 21 . A true knot of the umbilical cord may lead to e. g. fetal hypoxia, intrauterine growth restriction and even to fetal death.…”