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In 1847, only months after the first demonstration of anesthesia, James Simpson, an obstetrician, administered ether to a woman in labor for childbirth. He was quite impressed with the analgesia the new drug induced, as was his patient. Nevertheless, his journal notes on the case indicated his concern over the possible adverse effects of anesthesia on labor and delivery : “It will be necessary to ascertain anesthesia's precise effect, both upon the action of the uterus and on the assistant abdominal muscles; its influence, if any, upon the child; whether it has a tendency to hemorrhage or other complications.”
Thus began, more than a century and a half ago, perhaps the longest-lived controversy in the history of obstetric anesthesia, one that continues to this day in both academic and lay circles.
The modern debate has centered on several main issues:
Does regional analgesia for labor affect the length of labor or the rate of cervical dilation? In particular, does the timing of initiation of epidural analgesia play a role?
Does regional labor analgesia increase the risk for instrumental vaginal delivery?
Does regional labor analgesia increase the risk for cesarean delivery?
Does regional labor analgesia increase the risk for perineal injury?
Does regional labor analgesia increase the risk for postpartum depression?
No definitive study has adequately addressed any of these questions, and methodological problems have plagued all available evidence. The principal difficulty is that risk factors for dysfunctional labor also predispose a woman to request an epidural. This chapter will review the available literature, focusing on randomized controlled trials (RCTs) but considering other forms of evidence, and will emphasize the different conclusions reached by observational and prospective randomized designs.
Conventional wisdom holds that if started too early in labor (during the latent phase), epidural analgesia may markedly slow or even arrest the progress of labor. Amazingly, this once widely accepted clinical dogma has never been proved in carefully performed studies. Its origin can be traced to early case series of caudal or epidural anesthesia for labor, which probably resulted in dense sacral and lumbar blocks. In these uncontrolled reports, although some women in whom blocks were initiated very early may not have progressed through labor, it is unclear whether they would have progressed more quickly without the block.
Some nonrandomized studies have found an association between earlier epidural placement and dystocia. Thorp and colleagues compared various groups of nulliparous women defined by their early cervical dilation rate, their cervical dilation at the time of initiation of analgesia, and the choice of epidural or alternative analgesia. Among women with dilation less than 5 cm and dilation rate less than 1 cm/hr, epidural analgesia was associated with a sixfold increase in cesarean delivery for dystocia. Other comparisons demonstrated smaller relative risks or no difference. In a secondary analysis of the same group's randomized trial, the increased risk for cesarean delivery was greatest in women requesting analgesia earlier, although women were not randomly assigned to dilation at time of initiation of analgesia. Using a case-control methodology, Malone and colleagues identified epidural initiation at less than 2 cm dilation as a significant risk factor for prolonged nulliparous labor (odds ratio [OR] 42.7). In a sophisticated observational study using a variant of multivariate regression (propensity score analysis) to control for multiple simultaneous confounders, Lieberman and colleagues identified both cervical dilation less than 5 cm and station less than 0 at the time of epidural initiation as strong risk factors for cesarean delivery.
Evidence from RCTs has failed to confirm this finding ( Table 52.1 ). Chestnut and colleagues randomized women requesting epidural analgesia to early or late groups (approximately 4 and 5 cm dilation). No differences in labor outcome were seen in either spontaneous labors or induced labors. The early and late groups in these studies, however, were not markedly different in their cervical dilation at the time of epidural placement. Several more recent trials randomized women to early epidural placement or opioids until later in labor , , , or to intrathecal opioids followed by later epidural initiation. , , In each case, progress through the first stage of labor was either equivalent or faster in the early group than in the later group. No differences in second-stage duration or mode of delivery were found in any of the trials. Two meta-analyses of the RCTs, one performed before and two after the extremely large trial by Wang et al., found no difference in the mode of delivery between early and later epidural initiation. The difference between the RCTs and the retrospective studies may be because of selection bias, in that women requesting analgesia earlier in labor may be experiencing pain because of anatomic or physiologic factors predisposing them to dystocia. Interestingly, a recent prospective cohort study found that early epidural initiation (placed < 6 cm) was associated with lower fetal station during the active phase compared with later (> 6 cm) placement and that the early epidural group was also associated with a decreased risk for a prolonged second stage.
CERVICAL DILATION IN CM ( N ) | RESULTS | |||||
---|---|---|---|---|---|---|
Author, Year | Early | Late | Outcome | Early | Late | p |
Chestnut, 1994 , a | 4 (172) | 5 (162) | First stage (min) Second stage (min) CD (%) IVD (%) |
329 85 10 37 |
359 88 8 43 |
NS NS NS NS |
Chestnut, 1994 , b | 3.5 (74) | 5 (75) | First stage (min) Second stage (min) CD (%) IVD (%) |
318 91 18 43 |
273 77 49 19 |
NS NS NS NS |
Luxman, 1998 | 2.5 (30) | 4.5 (30) | First stage (min) Second stage (min) CD (%) IVD (%) |
342 41 7 13 |
317 38 10 17 |
NS NS NS NS |
Wong, 2005 , c | <4 (366) | >4 (362) | First stage (min) Second stage (min) CD (%) IVD (%) |
295 71 18 20 |
385 82 21 16 |
<.001 .67 .31 .13 |
Ohel, 2006 | 2.4 (221) | 4.6 (228) | First stage (min) Second stage (min) CD (%) IVD (%) |
354 95 13 17 |
396 105 11 19 |
.04 .12 .77 .63 |
Wong, 2009 , d | 2 (406) | 4 (400) | Labor duration (min) Second stage (min) CD (%) IVD (%) |
528 89 33 14 |
569 90 32 15 |
.047 .56 .65 .63 |
Wang, 2009 | 1.6 (6394) | 5.1 (6399) | Latent phase (min) Active phase (min) Second stage (min) CD (%) IVD (%) |
479 111 63 23 12 |
485 128 67 23 13 |
.22 .68 .87 .51 .10 |
Wang, 2011 , e | 2.2 (26) | 2.8 (28) | First stage (min) Second stage (min) CD (%) IVD (%) |
225 43 12 19 |
203 55 4 14 |
.69 .49 .36 .72 |
Parameswara , f | ≤2 | >2 | Labor duration (min) CD (%) |
476 22 |
471 23 |
.73 1.0 |
a Spontaneous labor; cervical dilation given as median.
b Oxytocin-receiving subjects; cervical dilation given as median.
c Spontaneous labor; subjects randomized at < 4 cm to intrathecal fentanyl 25 mcg or IM + IV hydromorphone; all subjects received epidural analgesia at second request for analgesia (systemic group) or > 4 cm or at third request for analgesia (intrathecal group). Median cervical dilation at first request was 2 cm in both groups, but cervical examination at initiation of epidural analgesia in late group was not reported.
d Nulliparas undergoing induction of labor, with cervical dilation given as median; analgesic protocol similar to Wong 2005. Total labor duration, but not first stage duration, was reported.
e All subjects received CSE (bupivacaine 2 mg, fentanyl 20 mcg) then were randomized to immediate or delayed (at request because of pain) epidural initiation. Cervical dilation at time of epidural start not reported.
f Abstract publication only; multiple details not reported. CD, Cesarean delivery; IVD, instrumental vaginal delivery.
The effect of epidural analgesia on cervical dilation in established labor, which corresponds to the length of the first stage of labor, is probably minimal. Some earlier retrospective studies finding slower cervical dilation were probably hampered by selection bias. A few older meta-analyses of randomized trials of epidural analgesia versus opioid analgesia have concluded that the first stage of labor is not prolonged by epidural analgesia. A recent systemic review did show that both the first (mean difference [MD] 32.28 minutes, 95% confidence interval [CI] 18.34 to 46.22; 2259 women; studies = 9) and second (MD 15.38 minutes, 95% CI 8.97–21.79; 4979 women; studies = 16; P < .00001) stages of labor were longer for epidural versus opioid analgesia. Nevertheless, heterogeneity was seen in the results, and the authors suggested publication bias may be possible. Curiously, this meta-analysis included slightly fewer studies examining length of first stage of labor than earlier analyses by the same group, which found no first stage differences ( Table 52.3 ), while including more studies of second stage duration. This study concluded that epidural initiation need not be delayed because early initiation does not increase incidence of instrumental births or cesarean delivery in nulliparous women.
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