The response of the umbilical artery pulsatility index in fetal sheep to acute and prolonged hypoxaemia and acidaemia induced by embolization of the uterine microcirculation

Abstract

In eight chronically-instrumented sheep, embolization of the uterine microcirculation was performed to evaluate the response of the umbilical artery pulsatility index to prolonged fetal hypoxaemia and acidaemia. From four days after surgery onwards, fetal arterial oxygen content [( O2]a) was progressively reduced by administration of microspheres into the uterine circulation. Measurements included fetal [O2]a, PO2, PCO2, pH, base excess, heart rate, blood pressure and umbilical artery pulsatility index. Fetal survival varied between less than 2 and less than 8 days, while mean fetal survival was less than 4 days. From baseline condition to the last evaluation preceding the diagnosis of fetal death, [O2]a decreased from 3.10 +/- 0.36 to 0.87 +/- 0.27 mM, pH decreased from 7.36 +/- 0.03 to 7.22 +/- 0.08, base excess decreased from -0.3 +/- 1.5 to -7.3 +/- 3.2 and blood pressure increased from 35.0 +/- 7.1 to 40.7 +/- 8.7 (means +/- SD). The umbilical artery pulsatility index (1.05 +/- 0.19 at baseline condition) did not significantly change (1.08 +/- 0.12 prior to fetal death). It is concluded that a condition of prolonged hypoxaemia and acidaemia in fetal sheep, induced by repeated embolizations of the uterine circulation, is not associated with consistent changes in the umbilical artery pulsatility index.