Fetal arterial pressure and heart rate changes in surviving and non-surviving immature fetal sheep following brief repeated total umbilical cord occlusions.

OBJECTIVES

To describe the changes in fetal heart rate and mean arterial pressure during repetitive total umbilical cord occlusions in immature sheep fetuses, resulting in severe asphyxia or fetal death. To describe the relationship between these changes and concurrent changes in acid-base status.

STUDY DESIGN

We performed brief repeated total umbilical cord occlusions, two out of every five min, in 14 immature sheep fetuses (at 90 days of gestation), until fetal mean arterial pressure dropped below 50% of baseline value during two successive occlusions. Fetal blood gas analyses were performed at regular intervals just before cord occlusions.

RESULTS

Progressive acidemia and hypotension developed with ongoing occlusions. The degree of hypotension during occlusions increased with ongoing occlusions. The minimum fetal arterial blood pressure during occlusions correlated well with the progressive acidemia. Six fetuses died at the end of the repetitive occlusion period. In the non-survivors, acidemia was more severe and paCO2 gradually increased during the entire repetitive occlusion period. In the survivors group, a period of transient hypoxia and hypotension was observed with a nadir at +60 min following the final occlusion.

CONCLUSION

Repetitive umbilical cord occlusions in immature sheep fetuses resulted in repetitive periods of hypotension, bradycardia, progressive fetal acidemia and ultimately fetal demise. Minimum fetal arterial blood pressure during occlusions correlated well with the progressive fetal acidemia.