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

References

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Results

The characteristics of the 261 study participants are summarized in Table 1. No fetal or neonatal deaths occurred. Umbilical artery cord blood was inadvertently not collected for one subject. Of the 261 women studied, 238 (91%) received pharmacologic analgesia during labor (nalbuphine, PCB, pudendal, caudal, or epidural) and 23 (9%) received none (not including local anesthesia). One hundred twenty-six (48%) received at least one (of a total 191 PCBs administered). One hundred ninety-seven (76%) received at least one dose of intravenous nalbuphine (a total of 237 doses were given). No narcotics other than nalbuphine were given. Ninety-nine women (38%) received both nalbuphine and a PCB.

Table 2 shows the reported degree of pain relief following administration of a PCB or nalbuphine. Including all doses, a substantial proportion of women reported excellent or good relief following PCB analgesia (70%) or nalbuphine (64%). Since nalbuphine is typically given earlier in the active phase of labor than a PCB, analysis was not appropriate to compare pain relief reported by medication type.

Using doses for which tracings were available, the best estimate overall incidence of bradycardia following PCB analgesia was 6.3% (10 of 157). Tracings were unavailable for 34 (18%) PCB administrations. If we were to make the unlikely assumption that all the doses with unavailable tracings had bradycardia, the rate could be as high as 23% (44 of 191).

Table 3 compares mean parameters according to whether women received a PCB. Prenatal factors were not significantly different between groups. There was no significant difference in mean umbilical artery pH, 1-minute Apgar score, 5-minute Apgar score, resuscitation with oxygen by mask, or length of newborn stay according to PCB exposure. Length of the first stage of labor was significantly longer (409 vs 338 minutes, P = .008) and arterial cord blood pCO2 was higher (49.2 vs 46.1 mm Hg, P = .004) among those who received a PCB.

There was no significant difference in umbilical artery cord blood gas values, 1-minute Apgar score, 5-minute Apgar score, need for resuscitation with oxygen by mask, or length of newborn stay according to nalbuphine exposure (data not shown). Women who received nalbuphine had a significantly longer first stage of labor (403 vs 278 minutes, P <.001), and tended to have a longer second stage of labor (38 vs 28 minutes, P = .052), but these women also had lower gravidity (2.2 vs 2.6, P = .040) and parity (0.8 vs. 1.3, P = .001).

To estimate the effect of PCB use on umbilical artery pH, we performed a forward stepwise linear regression Table 4. After adjusting for multiple possible confounders, the use of a PCB had no association with umbilical artery pH. The constant can be interpreted as the umbilical artery pH that would be expected in the absence of any of the predictor variables. The parameter estimates can be summed if 2 or more predictors are present. For example, if a woman had a second stage of labor lasting 1 hour and a pudendal block, the umbilical artery pH would be predicted to be 7.182 [7.236 + (-.032 + -.022) = 7.212]. When any PCB use was forced into the stepwise model, the regression coefficient (b) for PCB use was -.009 (P = 0.355.) The 95% confidence interval (CI) for the effect of a PCB on umbilical artery pH was very narrow (- 0.028 to 0.010), making it very unlikely we missed a clinically important effect.

Discussion

We found no statistically significant association between the use of a PCB and umbilical artery pH at birth. The results were similar in both the univariate analysis and in a regression analysis after adjusting for confounders. This suggests that known confounders do not affect the results, which makes it less likely that the results are affected by unknown confounders. The 95% CI for the effect of PCB is very narrow, making it unlikely that we have missed a clinically significant effect.

Supporting the lack of significant effect of PCB use is the bradycardia rate of only 6% in the 30 minutes afterward, using a very sensitive definition for bradycardia. This study is important, because we could not find any published studies of PCBs that used multivariate techniques to study their relationship with arterial cord blood gases and health of the neonate at birth. By using a prospectively designed study, it was possible to make certain that the information on likely confounding variables was collected uniformly for all of the patients in the study.

Our multivariate analysis showed that several factors are significantly associated with lower umbilical artery pH at birth. Among these were longer second stage of labor, intrauterine pressure catheter use, nuchal cord, and midforceps delivery. In agreement with our results, Yudkin and colleagues³⁶ found that increasing length of second stage of labor, vaginal operative delivery for fetal distress, and cord entanglement were associated with lower umbilical artery pH values at birth in multivariate analyses of unselected deliveries.