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

Abstract

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.

A comparative study of the safety of 0.25% levobupivacaine and 0.25% racemic bupivacaine for paracervical block in the first stage of labor

“…As was the case in our pilot study, Räsänen and Jouppila (11) could not detect any signs of vasoconstriction in the umbilical artery or maternal uterine artery after PCB in pregnancies without signs of chronic or acute fetal distress.…”

“…Recently, a need for further research and re‐evaluation of the safety aspects of PCB has been revealed (4,5). The most widely used anesthetic in PCB has been racemic bupivacaine (6–13).…”

A comparison of the hemodynamic effects of paracervical block and epidural anesthesia for labor analgesia

“…Indeed, PCB is generally only recommended for parturients having uncomplicated pregnancies ( 2, 6, 15). The incidence of fetal bradycardia has been reported to be in the range of 2–10% in recent studies and it still is the most common adverse effect observed after PCB ( 5, 6, 10). PCB‐induced fetal bradycardia has been attributed to vasoconstriction of the uterine arteries or increased uterine tonus induced by the local anesthetic agent, or the direct toxic effects of the local anesthetic agent on the fetus or a combination of any of the above mechanisms ( 10, 16).…”

“…We recorded a small but significant overall increase in the mean uterine artery PI after PCB that indicates an increase in uterine arterial impedance. There is one previous report on the effects of PCB on uteroplacental blood flow employing color Doppler ultrasound ( 10). These investigators noticed no significant overall changes in the PIs of any of the arteries they measured.…”

“…The effects of epidural analgesia on uteroplacental blood flow are well documented ( 7–9) but few reports exist on effects of PCB ( 10). Our study was designed to test the hypothesis that PCB would have a more profound effect than epidural analgesia on maternal and fetal blood flow.…”