To measure changes in cardiac output (CO) after partial cord occlusion in fetal sheep in order to investigate pathophysiological fetal adaptation mechanisms in a simulated acute placental insufficiency model under standardized conditions, with the aim of finding relevant methods for monitoring human fetuses during stress situations.METHODS
We used minimally invasive, percutaneous endoscopic techniques to close umbilical vessels in mid-gestational fetal sheep. Placental blood flow was reduced by preferentially closing first arterial and then the concomitant venous umbilical vessels within a short time interval. The investigations were carried out on 11 pregnant ewes at a median gestational age of 86 (range, 73–95) days. Major placental arteries and veins were occluded permanently by coagulation with bipolar forceps under percutaneous fetoscopic control. The fetal CO and Doppler parameters in the ductus venosus (DV), umbilical artery (UA) and umbilical vein (UV) were measured.RESULTS
In spite of heart rate reduction, the CO was not significantly affected by vessel occlusion (mean ± SD, 500 ± 194 mL/min before and 457 ± 219 mL/min after coagulation) because stroke volume slightly increased from 2.65 ± 1.16 mL/beat to 3.1 ± 1.5 mL/beat. The right to left CO ratio remained at 1.4. The UV flow/combined CO ratio decreased from 34 ± 14% to 25 ± 10% after vessel coagulation. The pulsatility index in the DV increased from 0.4 ± 0.1 to 0.7 ± 0.4. The DV blood flow volume remained relatively constant after the intervention. The DV shunting rate, given as DV/UV flow ratio, increased significantly from 30.8 ± 4.7% to 59.3 ± 25.0%.Conclusions
The nearly simultaneous closure of arterial and venous umbilical vessels changed the flow pattern in the UA and significantly reduced placental blood perfusion. It did not distinctly change the blood flow volume rate through the DV, and consequently the DV shunting rate was increased. The combined CO was not significantly affected by the vascular obstruction, whereas the fraction of combined CO directed to the placenta was reduced. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.