Effects of Autonomic Blockade with Spinal Anesthesia on Uterine and Fetal Hemodynamies and Oxygen Consumption in the Sheep

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Abstract
The effects of partial blockade of the autonomic nervous system with spinal anesthesia on utero-placental and fetal circulation and O2 consumption were studied in near term pregnant sheep. The effects of administering metaraminol and O2 during the blockade were also investigated. A 50% decrease in maternal arterial pressure accompanied by 60% decrease in utero-placental blood flow occurred. Utero-placental O2 consumption decreased by only 20%. Fetal arterial and venous pressures and umbilical blood flow were not affected. Umbilical vein blood pO2 [oxygen pressure decreased but fetal O2 consumption remained unchanged. Administration of metaraminol during the spinal blockade restored utero-placental circulation and O2 consumption to control values without altering fetal hemodynamics and O2 utilization. Administration of O2 to the mother increased maternal blood pO2, but had no effects on the utero-placental circulatory alterations of spinal blockade; it did not alter fetal circulation and O2 utilization.