Seven chronically catheterized fetal sheep at 125-140 days gestation were studied in 12 experiments to determine the direct effects of the local anesthetic bupivacaine (infused intravenously to the fetus) on the umbilical circulation and placental gas exchange. Electrocortical activity, umbilical blood flow, heart rate, and umbilical arterial and venous pressures were continuously monitored in experiments comprising a baseline period, a drug infusion period and a recovery period, each of 2 hr duration. Samples of umbilical arterial and venous blood were taken for blood gas analysis, and for bupivacaine assay using high pressure liquid chromatography technique. Fetal plasma bupivacaine levels were 1.3 +/- 0.3 microgram/ml (mean +/- SEM) between 60-120 min of infusion. Heart rate and umbilical blood flow decreased significantly to 89 and 94% of control, respectively, (P less than 0.05) during the infusion and returned to control levels by 2 hr afterwards. Mean umbilical arterial and venous pressures were not significantly altered, and no significant rise in umbilical vascular resistance occurred. No changes occurred in umbilical arterial or venous pH, PO2, or PCO2. In summary, bupivacaine reversibly depressed fetal heart rate and umbilical blood flow without detrimental changes in fetal blood gas or acid-base status.
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