Does a paracervical block with bupivacaine change vascular resistance in uterine and umbilical arteries?

Paracervical block during labor following normal, uncomplicated pregnancy is occasionally accompanied by fetal bradycardia. To evaluate whether a paracervical block with bupivacaine causes changes in the vascular resistance of uteroplacental and umbilicoplacental blood flow, a total of 12 singleton, uncomplicated pregnancies in active labor at the end of pregnancy were included to this study. By using pulsed color Doppler ultrasound techniques the pulsatility indices were measured from both uterine and umbilical arteries before, one minute and 20 minutes after a paracervical block with bupivacaine. Pulsatility indices of both uterine and umbilical arteries remained unchanged throughout the study period, as did fetal and maternal heart rates. In two cases fetal bradycardia developed, causing a marked increase in the vascular resistance of the umbilical artery one minute after the paracervical block. In the uterine arteries there was only a minor increase. When the fetal bradycardia ceased the pulsatility indices returned to the levels at the beginning of the study. Paracervical block with bupivacaine in normal pregnancies without signs of chronic or acute fetal distress does not change the vascular resistance in the uterine or umbilical arteries. If fetal bradycardia develops, it seems to be due to the direct effect of bupivacaine on the fetus, mainly on the umbilical vessels.