Is Paracervical Block Safe and Effective? A Prospective Study of Its Association with Neonatal Umbilical Artery pH Values

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Original Research

Is Paracervical Block Safe and Effective? A Prospective Study of Its Association with Neonatal Umbilical Artery pH Values

J Fam Pract. 1999 October;48(10):778-784

By

Barcey T. Levy, PhD, MD

References

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BACKGROUND: Paracervical blocks (PCBs) relieve labor pain, but reports of associated complications have caused many physicians to question their safety.

METHODS: We designed a prospective observational study to examine the association between PCBs and umbilical artery hydrogen ion concentration (pH) values. A total of 261 healthy women in labor were recruited from a community hospital. Physicians used 1% lidocaine for the PCBs. We used multivariate linear regression to model predictors of umbilical artery pH at birth.

RESULTS: Of the women studied, 238 (91%) received analgesia during labor (nalbuphine, PCB, pudendal, caudal, or epidural). Of these, 126 (48%) received at least one PCB (191 were given), and 197 (76%) received at least one dose of nalbuphine (237 were given). Univariate analyses showed no significant differences in mean 1-minute Apgar scores, 5-minute Apgar scores, umbilical artery pH, resuscitation with oxygen by mask, or length of newborn stay according to either PCB or nalbuphine exposure. Factors significantly associated with lower umbilical artery pH in a linear regression analysis included longer second stage of labor (-0.032 pH units for each 1-hour increase; 95% confidence interval [CI], -.046 to -.018), pudendal block (-0.022; 95% CI, -.040 to -.004), intrauterine pressure catheter use (-0.029; 95% CI, -0.053 to -.006), nuchal cord (-0.027; 95% CI, -.051 to -.004), and midforceps delivery (-0.080; 95% CI, -.159 to .000). Increasing maternal age and induction with either artificial rupture of membranes or gel were associated with higher umbilical artery pH values.

CONCLUSIONS: After adjusting for other variables, neither PCB nor nalbuphine use were associated with umbilical artery pH at birth. PCBs using 1% lidocaine injected superficially should be considered a safe and effective form of obstetric analgesia. PCBs may be especially useful for women giving birth in hospitals where other obstetric anesthesia services are not readily available.

Many women want medical management of pain during labor.¹ There are several commonly used interventions, including intravenous narcotics, epidural anesthesia, and pudendal blocks.² Effective pain management is important, because obstetric pain can lead to harmful effects, such as reduced uterine blood flow and decreased fetal oxygenation.^3,4 Pharmacologic pain control should be viewed as an adjunct to psychological support.⁵

Paracervical blocks (PCBs) have been in use for several decades and are routinely used for obstetric analgesia in Scandinavian countries.^6,7 They effectively relieve pain during the first stage of labor,^8-12 but reports of complications, such as fetal bradycardia^13-15 and intrapartum fetal or neonatal death,^15-18 have caused many physicians to question their safety. Two extensive reviews involving more than 70,000 PCBs found that many of the fetal and neonatal deaths associated with them could be explained by factors unrelated to the PCBs.^19,20 Additionally, the standard technique for PCB use has changed. Submucosal injection in the vaginal fornices to a depth of no more than 2 to 4 mm and the use of lower concentrations of local anesthetics reduce risks to the woman and the fetus.^{8,9,11,12,21-24}

Fetal bradycardia following a PCB administered with submucosal injection has a reported incidence of 2% to 13%.^8,11,12 Bradycardia can lead to fetal acidosis, which resolves in utero.^14,15,20 It is difficult to accurately compare bradycardia rates among studies, because some studies have used a variety of agents for PCBs8 or varying definitions of post-PCB bradycardia.^8,11,12

Several larger nonrandomized studies using univariate techniques to compare Apgar scores in women given a PCB with a control group have reported either better scores in the PCB group²⁵ or no difference.^8,11

Umbilical acid-base status at delivery is recognized as a reliable indicator of fetal oxygenation and well-being^26,27 and is more objective than the Apgar score.^28,29 We reasoned that if PCB use has a significant impact on the fetus, this could be assessed by examining the umbilical artery hydrogen ion concentration values (pH) at birth. There is controversy about the level of pH below which a neonate is at significantly greater risk for neurologic sequelae or death, and a variety of values have been proposed.^26,30,31 However, increasing severity of metabolic acidosis at birth is associated with an increased likelihood of newborn encephalopathy and motor and cognitive deficits at the age of 1 year.^32,33 Thus, umbilical artery pH is an appropriate intermediate outcome to assess the potential risks of PCB.

Our purpose was to determine whether there is an association between use of a PCB and umbilical artery pH values at birth. A MEDLINE search of the literature written in English from 1966 to the present using the terms “analgesia, obstetric,” “neonatal outcome(s),” and “acid-base status” revealed no studies of PCBs that prospectively examined them with an appropriate comparison group and reported on neonatal umbilical artery blood gas values while simultaneously controlling for possible confounders. Our study expands on previous studies of PCB anesthesia by using umbilical artery pH at birth as the main outcome variable and by prospectively collecting information about and controlling for use of analgesics other than PCBs and other prenatal and obstetric factors that may confound results.