Duration of Labor

First Stage of Labor

The effect of neuraxial labor analgesia on the duration of the first stage of labor was addressed as a secondary outcome variable in many of the randomized controlled trials. A 2011 meta-analysis3 of 11 studies found no difference in the duration of the first stage of labor between women who were randomly assigned to receive epidural analgesia and those assigned to receive systemic opioid analgesia, although the confidence interval was wide, indicating significant heterogeneity among studies (Table 23-12). There was significant heterogeneity in the outcome because of the mixed parity of the patient populations and differences among studies in the definition of the duration of the first stage of labor. In contrast, the individual meta-analysis of the Parkland Hospital data showed a significant prolongation of the first stage of labor (approximately 30 minutes) in nulliparous women who were randomly assigned to receive epidural analgesia.429

Wong et al.21 and Ohel et al.22 assessed duration of labor as a secondary outcome in their randomized controlled trials of the initiation of neuraxial analgesia during early labor. Both groups of investigators determined that the duration of the first stage of labor, and thus consequently the overall duration of labor, were significantly shorter in women randomly assigned to receive early labor neuraxial analgesia than in those assigned to receive systemic opioid analgesia. In the Wong et al. study,21 the median difference in the overall duration of labor between the early and late neuraxial analgesia groups was 81 minutes (95% CI, 28 to 123).

Determining the duration of labor requires that investigators document start and end times. The definition of the start time varies among studies but is usually consistent between groups within a study. The end of the first stage of labor is defined as the time of full (10 cm) cervical dilation. This point can be determined only with manual cervical examination. Most studies do not mandate regular cervical examinations by study protocol, or if they do, the intervals are fairly long (e.g., 1 to 2 hours). Clinically, full cervical dilation is diagnosed when a cervical examination is performed because the patient complains of rectal pressure. It is likely that women with effective epidural analgesia will complain of rectal pressure at a later time (and lower fetal station) than women with systemic opioid analgesia. In other words, the patient may be fully dilated for a significant time before cervical examination verifies full cervical dilation. This difference serves to artificially prolong the duration of the first stage of labor in the epidural group, although it shortens the apparent duration of the second stage of labor.

Other factors may also influence the duration of the first stage of labor. Some clinicians have noted enhanced uterine activity in some patients for approximately 30 minutes after the initiation of neuraxial analgesia, whereas uterine activity appears to be reduced in other patients. Schellenberg468 suggested that aortocaval compression is responsible for the transient decrease in uterine activity that occurs after the administration of epidural analgesia in some patients. He concluded that this effect does not occur if aortocaval compression is avoided. Cheek et al.469 noted that uterine activity decreased after the intravenous infusion of 1 L of crystalloid solution, but not after infusion of 0.5 L or maintenance fluid alone. There was no decrease in uterine activity after the administration of epidural analgesia. Zamora et al.36 made similar observations. Miller et al.470 hypothesized that a fluid bolus might inhibit antidiuretic hormone (vasopressin) release from the posterior pituitary gland. Because this organ also releases oxytocin, the production of that hormone might also be transiently suppressed; this possible decrease in oxytocin release may partially explain the transient changes in uterine contractility observed in association with epidural analgesia.

In a prospective but nonrandomized study, Rahm et al.471 observed that epidural analgesia (bupivacaine with sufentanil) was associated with lower plasma oxytocin levels at 60 minutes after initiation of analgesia than in healthy controls who did not receive epidural analgesia. Behrens et al.472 noted that epidural analgesia during the first stage of labor significantly reduced the release of prostaglandin F2α and “impede[d] the normal progressive increase in uterine activity.” In contrast, Nielsen et al.473 measured upper and lower uterine segment intrauterine pressures for 50 minutes before and after the administration of epidural bupivacaine analgesia in 11 nulliparous women during spontaneous labor. No significant difference in the number of contractions before and after epidural analgesia was observed. There was greater intrauterine pressure in the upper uterine segment than in the lower segment (consistent with fundal dominance) both before and after initiation of epidural analgesia. Further, fundal dominance was higher after epidural analgesia than in the preanalgesia period.

Increased uterine activity after the initiation of neuraxial analgesia has been hypothesized to be an indirect effect of neuraxial analgesia (see later discussion).474 Initiation of neuraxial analgesia is associated with an acute decrease in the maternal plasma concentration of circulating epinephrine.4 Epinephrine is a tocolytic, and the acute decrease in maternal concentration may result in greater uterine activity. This may be an explanation for the salutary effect on the progress of labor that is observed in some women with dysfunctional labor after the initiation of neuraxial analgesia475 or in women who are extremely anxious.476

The epidural administration of a local anesthetic with epinephrine is followed by systemic absorption of both drugs. Some physicians have expressed concern that the epinephrine may exert a systemic beta-adrenergic tocolytic effect and slow labor. Early studies, which used large doses of epinephrine, suggested that the caudal epidural administration of local anesthetic with epinephrine prolonged the first stage of labor and increased the number of patients who required oxytocin augmentation of labor.477 Subsequently, most studies have suggested that the addition of epinephrine 1.25 to 5 µg/mL (1 : 800,000 to 1 : 200,000) to the local anesthetic solution does not affect the progress of labor or method of delivery.*

There is no evidence that the specific local anesthetic or opioid used for neuraxial analgesia directly or indirectly affects the duration of labor.86,479 In a randomized controlled trial, Tsen et al.480 observed a higher rate of cervical dilation in women who received CSE analgesia than in those who received epidural analgesia. However, randomized controlled trials that compared CSE and epidural analgesia have not found a difference in the duration of labor between the two techniques.430-432,434,481

New evidence suggests that genetic polymorphism in the oxytocin receptor, catechol-O-methyltransferase (COMT), and β2-adrenergic receptor (ADRB2) genes affect the progress of labor.482,483 Whether these genotypes interact with neuraxial analgesia to affect the progress of labor requires further study with large numbers of parturients.

In summary, neuraxial analgesia appears to have a variable effect on the duration of the first stage of labor. It may shorten labor in some women and lengthen it in others. However, analgesia-related prolongation of the first stage of labor, if it occurs, is short, has not been shown to have adverse maternal or neonatal effects, and is probably of minimal clinical significance.

Second Stage of Labor

There is little doubt that effective neuraxial analgesia prolongs the second stage of labor. Meta-analyses of randomized controlled trials that compared neuraxial with systemic opioid analgesia support this clinical observation (see Table 23-12).3,429 The mean duration of the second stage was 15 to 20 minutes longer in women randomly assigned to receive neuraxial analgesia than in women assigned to receive systemic opioid analgesia.3,429

The ACOG has defined a prolonged second stage in nulliparous women as lasting more than 3 hours with neuraxial analgesia and more than 2 hours without neuraxial analgesia; for parous women, it is more than 2 hours in those with neuraxial analgesia and more than 1 hour in those without neuraxial analgesia.484 Zhang et al.485 performed a secondary analysis of data from the Consortium on Safe Labor, a large, multicenter study from 19 hospitals across the United States, to characterize the duration of labor in a contemporary cohort of American women. Data were abstracted for term parturients in spontaneous labor with a singleton gestation in the vertex presentation and with normal perinatal outcome. The 95th percentiles for duration of the second stage of were 3.6 and 2.8 hours for nulliparous women with and without epidural analgesia, respectively ( Table 23-13). Thus, these contemporary data suggest that a significant proportion of women will have a “prolonged” second stage, as defined by the ACOG criteria.

Rouse et al.486 studied the relationship between second-stage duration and maternal and neonatal outcomes in nulliparous women by performing a secondary analysis of data collected as part of a multicenter study between 2002 and 2005. The rate of spontaneous vaginal delivery declined as the duration of the second stage of labor increased; however, over 55% of women whose second-stage duration was 3 hours or longer still went on to deliver vaginally.486 The risk for chorioamnionitis, third- or fourth-degree perineal laceration, and uterine atony was greater in women with a prolonged second stage duration; however, after adjusting for mode of delivery, adverse neonatal outcomes did not differ in women whose second stage duration was 3 hours or longer, compared with those women with a shorter second-stage labor duration. The authors concluded that the second stage of labor does not need to be terminated based on duration alone. Extending the duration of the second stage will allow a significant number of women to deliver vaginally.

Other studies have confirmed that a delay in delivery is not harmful to the infant or mother provided that (1) electronic FHR monitoring confirms the absence of nonreassuring fetal status, (2) the mother is well hydrated and has adequate analgesia, and (3) there is ongoing progress in the descent of the fetal head.484 The ACOG has stated that if progress is being made, the duration of the second stage alone does not mandate intervention.484 A 2012 workshop was convened by the National Institute of Child Health and Human Development, the Society for Maternal-Fetal Medicine, and the ACOG with the goal of recommending practices that prevent primary cesarean delivery. The group concluded that a cesarean delivery for second-stage arrest in nulliparous women with epidural analgesia should not be considered unless there is no progress (descent or rotation) for more than 4 hours (Box 23-10).487 Thus, the decision as to whether to perform an operative delivery in the second stage or allow continued observation should be made on the basis of clinical assessment of the woman and the fetus and the skill and training of the obstetrician.

Second-Stage Management: Immediate versus “Delayed” Pushing.

Many women are asked to begin “pushing” as soon as full cervical dilation has been confirmed, regardless of the fetal station. Some practitioners have suggested that “delayed” pushing might result in less maternal exhaustion and better maternal and fetal outcomes. Several studies have sought to determine whether immediate or delayed pushing for women with epidural analgesia during the second stage of labor affects labor duration and outcome.488-498 Data are conflicting. A 2012 meta-analysis of studies that compared early and delayed pushing included nine high-quality and three low-quality randomized controlled trials involving approximately 3000 women.499 Analysis of only the high-quality studies showed that delayed pushing did not influence the rate of spontaneous vaginal delivery (59.0% versus 54.9%; pooled RR, 1.07; 95% CI, 0.98 to 1.26) (Figure 23-14) or the rate of second-stage cesarean delivery. The total duration of the second stage was longer with delayed pushing (weighted mean difference, 57 min; 95% CI, 42 to 72), although duration of pushing was shorter. Heterogeneity in the reporting of neonatal outcomes among the trials precluded meta-analysis. One large study reported a higher incidence of low (< 7.10) umbilical arterial blood pH in the delayed pushing group491; however, other studies found no difference between groups in this outcome or in Apgar scores. The authors concluded that there are few clinical differences in outcomes between early and delayed pushing but that effects on maternal and neonatal outcomes remain unclear.

Although there do not appear to be any major advantages to delayed pushing, it does not seem reasonable to ask the mother to push from a high fetal station. It is common for anesthesia providers to be asked to decrease or discontinue neuraxial analgesia because the mother does not feel the urge to push when she is fully dilated. However, women with effective neuraxial analgesia do not feel the urge to push at a high fetal station. The density of neuraxial analgesia should not be decreased until the fetus has descended. If evaluation at this point determines that the mother still does not feel the urge to push, the maintenance dose may be reduced. Discontinuing the maintenance of analgesia is rarely indicated because analgesia/anesthesia may be difficult to reestablish if the need for operative delivery arises.

Third Stage

Rosaeg et al.500 retrospectively reviewed the outcomes of 7468 women who underwent vaginal delivery at their hospital between 1996 and 1999. Epidural analgesia was not associated with a prolonged third stage of labor. The duration of the third stage of labor was shorter in women who received epidural analgesia and subsequently required manual removal of the placenta. The researchers suggested that epidural analgesia “provided a ‘permissive’ role”—in other words, epidural analgesia likely facilitated and/or encouraged earlier intervention by the obstetrician.

Other Factors and Progress of Labor

Oxytocin

Active management of labor is a concept that consists of a disciplined, standardized labor management protocol that includes early amniotomy and oxytocin augmentation if the cervix fails to dilate at a minimum rate (usually 1 cm/h in nulliparous women). Early studies suggested that this type of labor management decreased the rate of cesarean delivery.501 More recently, meta-analysis of a number of randomized controlled trials suggests that active management of labor may have little effect on the cesarean delivery rate.502 Although randomized trials of neuraxial compared with systemic opioid analgesia have consistently found that neuraxial analgesia does not cause an increase in the rate of cesarean delivery (see earlier discussion), Kotaska et al.503 questioned the external validity of these trials because of oxytocin management. In a search of the medical literature, they identified 16 randomized controlled trials; 8 of the 16 trials included descriptions of labor management and these trials were included in the analysis. Seven of the eight trials described active management of labor and found no difference in the mode of delivery between groups. Only one of eight trials described the use of low-dose oxytocin and reported a markedly higher rate of cesarean delivery in the neuraxial analgesia group. Kotaska et al.503 concluded that epidural analgesia in the setting of low-dose oxytocin probably increases the rate of cesarean delivery. The researchers were correct in stating that the role of oxytocin in neuraxial analgesia outcome studies has not been well controlled. However, their conclusion that epidural analgesia in the setting of low-dose oxytocin probably causes an increase in the rate of cesarean delivery is highly flawed because, in their analysis, the researchers did not include the eight studies that did not describe the management of labor. In all probability the management of labor in these studies was not active (e.g., did not include high-dose oxytocin administration), or this would have been described.

In randomized controlled trials that compared the effects of neuraxial and systemic opioid analgesia on the outcome of labor, women who received neuraxial opioids had a higher rate of oxytocin augmentation.3,429 In a meta-analysis that included 13 randomized trials, the risk ratio was 1.19 (95% CI, 1.03 to 1.39).3 The reason(s) for this observation are not clear.

Randomized controlled trials that compared early and late initiation of neuraxial analgesia have used markedly different oxytocin protocols, yet all have concluded that early initiation of neuraxial analgesia does not have an adverse effect on the outcome of labor. In the study of early CSE analgesia by Wong et al.,21 the rate of oxytocin use was high in both groups (approximately 93%). However, the maximum oxytocin infusion rate in the control (early systemic opioid) group was significantly higher than that in the early CSE group even though the median duration of labor was 81 minutes shorter in the CSE group. In the study of early epidural analgesia by Ohel et al.,22 the rate of oxytocin use in both groups was much lower (approximately 29%); however, as in the study by Wong et al.,21 the duration of labor was significantly shorter in the early neuraxial analgesia group. Taken together, the results of these studies do not support the hypothesis that oxytocin played a major role in the outcomes.

The ACOG supports the use of oxytocin for the treatment of dystocia or arrest of labor in the first or second stage, whether or not the patient is receiving neuraxial analgesia.484

Ambulation

Observational studies suggest that ambulation may be associated with less pain and a shorter duration of labor.504 However, randomized controlled trials that compared ambulation and bed rest during the first stage of labor in women with neuraxial analgesia have not demonstrated any advantages of ambulation with regard to the progress or outcome of labor. Nageotte et al.432 randomly assigned 505 nulliparous women to receive CSE analgesia either with or without ambulation. There was no difference between groups in the mode of delivery or duration of labor. These results agree with those of a meta-analysis of five randomized controlled trials involving 1161 women.505 In addition, there were no differences between groups in the use of oxytocin augmentation, satisfaction with analgesia, or Apgar scores. No adverse effects were reported. These results are similar to those of trials that compared ambulation and bed rest in women without neuraxial analgesia.506

Effects of Neuraxial Analgesia on the Fetus and Neonate

Neuraxial analgesia may affect the fetus directly, indirectly, or both. First, systemic absorption of the anesthetic agents may be followed by transplacental transfer of the drug, which has a direct effect on the fetus. Second, the effects of neuraxial blockade on the mother may affect the fetus indirectly. Effects of local anesthetics and opioids on the fetus and neonate are discussed in detail in Chapter 13.

Direct Effects

Direct fetal effects include intrapartum drug effects on the FHR as well as possible respiratory depression after delivery. The determinants of maternal plasma drug concentration, transfer across the placenta, and effects on the neonate are discussed in Chapters 4 and 13. Determinants of maternal plasma drug concentration include dose, site of administration, metabolism and excretion of the drug, and the presence of adjuvants (e.g., epinephrine). Factors that influence placental transfer include maternal and fetal placental perfusion, the physicochemical characteristics of the drug, concentration of the free drug in maternal plasma, and permeability of the placenta. Most anesthetic and analgesic drugs, including local anesthetics and opioids, readily cross the placenta.

Fetal Heart Rate

Effects of local anesthetics and opioids on FHR may be direct and indirect (see earlier discussion)474,479; however, there is little evidence for a direct effect when these drugs are administered as components of neuraxial analgesia. Transient changes in FHR variability and periodic decelerations have been observed during epidural labor analgesia with bupivacaine and other local anesthetics.479,507,508 These FHR decelerations were not associated with maternal hypotension. However, Loftus et al.509 did not observe FHR decelerations in women who received epidural bupivacaine for elective cesarean delivery, despite the use of larger doses of bupivacaine and the occurrence of more extensive sympathetic blockade in comparison with epidural labor analgesia. Of interest, one study noted that the administration of either epidural bupivacaine or intrathecal sufentanil was followed by a similar incidence of FHR decelerations (23% and 22%, respectively) in laboring women.510 Other studies have not observed a higher incidence of FHR decelerations associated with epidural administration of bupivacaine during labor.511 Further, the reports of FHR decelerations after bupivacaine did not demonstrate adverse neonatal outcome; thus, the significance of these decelerations is unclear. There are no published data on the relationship between the concentration of bupivacaine used for intrapartum epidural analgesia and the incidence of FHR decelerations. Altogether, these data suggest that epidural local anesthetics have minimal, if any, direct effect on FHR.

Similarly, neuraxial opioid administration has little direct effect on the FHR.109,512,513 In contrast, systemic meperidine analgesia was associated with a greater reduction of FHR variability and fewer FHR accelerations than epidural bupivacaine analgesia.514 Spinal administration of local anesthetics and opioids results in lower maternal plasma concentrations of drug(s) than epidural administration and is therefore even less likely to cause a direct fetal effect.

Neonatal Depression

Systemic absorption of local anesthetic or opioid may have neonatal effects. This occurs more often after the systemic administration of opioid for labor analgesia.21,515 The neonatal depressant effects of drugs administered to the mother in the intrapartum period are usually assessed with neurobehavioral testing. Unfortunately, these tests are quite subjective and lack specificity. Additionally, scientifically rigorous studies are lacking, and most of the local anesthetic studies were performed in the era when high-dose epidural analgesia was common; these observational studies found that local anesthetics administered as components of epidural analgesia were sometimes associated with minor, transient effects on neonatal behavior.86,479,516

When given by continuous epidural infusion, epidural opioid administration rarely results in accumulation of the drug and subsequent neonatal respiratory depression.* Bader et al.220 noted that a continuous epidural infusion of 0.125% bupivacaine with fentanyl 2 µg/mL over a period of 1 to 15 hours did not result in significant fetal drug accumulation or adverse neonatal effects (in this study, the maximal cumulative dose of fentanyl was 300 µg). Porter et al.221 reported no adverse effect of fentanyl on neurobehavioral scores or other indices of fetal welfare when patients received an epidural infusion of 0.0625% bupivacaine with or without fentanyl 2.5 µg/mL. The mean ± SD maternal dose of fentanyl was 183 ± 75 µg (range, 53 to 400 µg). Loftus et al.109 observed only a modest reduction in NACS at 24 hours in neonates whose mothers had received epidural fentanyl during labor; neonates exposed to sufentanil during labor had a somewhat higher NACS at 24 hours, and sufentanil was detected in the umbilical arterial blood in only one of nine samples. Vertommen et al.107 observed no difference in Apgar scores or NACS in neonates whose mothers were randomly assigned to receive epidural sufentanil (up to 30 µg) during the course of labor and a control group that did not receive sufentanil.107 Maternal sufentanil levels were below the sensitivity of the assay (0.1 ng/mL) after an epidural bolus of 10 µg.114

Intrathecal administration of an opioid during labor would be expected to have even fewer direct effects on the fetus than epidural administration. Smaller doses of opioid are administered, and less drug is absorbed systemically.

Indirect Effects

The indirect fetal effects of epidural and intrathecal opioids may be more significant than the direct effects. Obviously, if the mother has severe respiratory depression and hypoxemia, fetal hypoxemia and hypoxia will follow.357 More common is the occurrence of fetal bradycardia after initiation of neuraxial analgesia. The presumed cause is that the rapid onset of analgesia results in decreased plasma concentrations of catecholamines.474 Epinephrine causes uterine relaxation by stimulating β2-adrenergic uterine receptors. A reduced circulating concentration of epinephrine may result in increased uterine tone. Because uteroplacental perfusion occurs during periods of uterine diastole (i.e., uterine relaxation), uterine tachysystole may result in decreased uteroplacental perfusion and fetal hypoxia.

Published observations suggest that uterine tachysystole and fetal bradycardia may follow the administration of either intrathecal or epidural analgesia during labor. Abrão et al.518 randomized 72 laboring women to receive either CSE or epidural analgesia, and they observed the incidence of FHR abnormalities (prolonged deceleration or bradycardia) and an elevation in uterine tone (defined as an increase of 10 mm Hg or more in basal uterine pressure). The incidences of FHR abnormalities (32% versus 6%), and FHR abnormalities combined with an increase in uterine pressure (27% versus 3%), were significantly higher in the CSE group than in the epidural group. However, a significant limitation of this study is that the outcomes were assessed for only 15 minutes after the initiation of analgesia and the analgesic techniques were not equipotent.519 The overall high incidence of FHR abnormalities noted in the study may have been due to the initiation of analgesia in women in advanced labor.

Fortunately, fetal bradycardia after labor analgesia does not appear to increase the overall risk for adverse outcome. Albright and Forster520 retrospectively reviewed outcomes for 2560 women who delivered at their hospital between March 1995 and April 1996. Approximately half of the patients received CSE analgesia (10 to 15 µg of intrathecal sufentanil), and the other half received either systemic opioids or no medication. There was no difference between the two groups in the incidence of emergency cesarean delivery (1.3% versus 1.4%, respectively). Mardirosoff et al.521 performed a systematic review of reports of randomized comparisons of intrathecal opioid analgesia with any nonintrathecal opioid regimen in laboring women. The investigators noted that intrathecal opioid analgesia was associated with a significant increase in the risk for fetal bradycardia (OR, 1.8; 95% CI, 1.0 to 3.1). However, the risk for cesarean delivery for FHR abnormalities was similar in the two groups (6.0% versus 7.8%, respectively). Van de Velde et al.522 randomly assigned laboring women to one of the following three treatment regimens: intrathecal sufentanil 7.5 µg, intrathecal sufentanil 1.5 µg/bupivacaine 2.5 mg/epinephrine 2.5 µg, and epidural bupivacaine 12.5 mg/sufentanil 7.5 µg/epinephrine 12.5 µg. Although the incidence of FHR abnormalities was higher in the high-dose intrathecal sufentanil group, there was no difference among groups in the need for emergency cesarean delivery.

Given the risk for fetal bradycardia with neuraxial analgesia in laboring women, the FHR should be monitored during and after the administration of either epidural or intrathecal analgesia. Treatment of fetal bradycardia includes (1) relief of aortocaval compression; (2) discontinuation of intravenous oxytocin; (3) administration of supplemental oxygen; (4) treatment of maternal hypotension, if present; and (5) fetal scalp stimulation. Persistent uterine tachysystole should also prompt the administration of a tocolytic drug (e.g., terbutaline or nitroglycerin).

Conclusions and Recommendations

Philosophy of Labor Analgesia

An unacceptably high number of women involuntarily experience severe pain during labor. As noted by the ASA and the ACOG, “There is no other circumstance where it is considered acceptable for a person to experience severe pain, amenable to safe intervention, while under a physician's care.”18,19 Unfortunately, labor represents one of the few circumstances in which the provision of effective analgesia is alleged to interfere with the parturient's and obstetrician's goal (e.g., spontaneous vaginal delivery). Dense neuraxial anesthesia may adversely affect the progress of labor in some patients. Indeed, given the complicated neurohumoral and mechanical processes involved in childbirth, it would be unreasonable to expect that neuroblockade of the lower half of the body would not have an effect on this process, whether positive or negative. However, maternal-fetal factors and obstetric management—not the use of neuraxial analgesia—are the most important determinants of the outcome of labor. Anesthesia providers should identify those methods of analgesia that provide the most effective pain relief without unduly increasing the risk for obstetric intervention. Operative delivery increases the risk for maternal morbidity and mortality and is more expensive than spontaneous vaginal delivery. Randomized trials suggest that the use of neuraxial analgesia does not increase the cesarean delivery rate but may adversely influence the instrumental vaginal delivery rate.3 Further, neuraxial analgesia may occasionally, either directly or indirectly, have adverse—usually temporary—effects on the fetus.

Despite these risks, many women opt for neuraxial analgesia because no other method of labor analgesia provides its benefits (almost complete analgesia), and the risks are acceptably low. Even no analgesia may be more hazardous to some women than neuraxial analgesia (e.g., patients with an anticipated difficult airway or those at high risk for emergency cesarean delivery). Therefore, it is the duty of the anesthesia provider to provide appropriate (albeit not always total) pain relief during the first and second stages of labor. Analgesia should be tailored to the individual patient's labor, medical condition, preferences, and goals. Most women strongly dislike dense motor blockade, and many prefer to maintain some sensation of uterine contractions and perineal pressure, especially during the second stage of labor. However, a few women may accept the probable increase in risk for instrumental vaginal delivery in exchange for dense analgesia.

A Practical Guide to Neuraxial Labor Analgesia

Initiation of Analgesia

Neuraxial labor analgesia may be initiated with either the intrathecal (CSE) or the epidural injection of analgesic/anesthetic agents. The decision regarding the specific technique and choice of drugs and doses is individualized for each parturient. Parity, stage and phase of labor, use of intravenous oxytocin, and the presence of any coexisting disease(s), as well as the status of the fetus, are all considered in the decision.

In healthy nulliparous women in early labor (< 4 to 5 cm cervical dilation), my colleagues and I often initiate CSE analgesia with an intrathecal opioid alone (e.g., fentanyl 25 µg or sufentanil 5 µg), followed by placement of an epidural catheter and administration of a standard lidocaine 45 mg/epinephrine 15 µg epidural test dose. Some anesthesia providers initiate intrathecal analgesia with both an opioid and a local anesthetic. The addition of a local anesthetic is unnecessary for achieving complete spinal analgesia during early labor; it may increase the risk for hypotension and result in motor blockade in some patients, particularly if it is followed by injection of an epidural test dose that contains a local anesthetic. However, the intrathecal administration of both an opioid and a local anesthetic achieves a longer duration of analgesia and lower incidence and severity of pruritus than intrathecal injection of an opioid alone.

Alternatively, epidural analgesia can be initiated with injection of a low-concentration local anesthetic solution (bupivacaine 0.0625% to 0.125%) combined with an opioid (fentanyl 50 to 100 µg). The epidural catheter is sited and a standard epidural test dose is injected, followed by administration of 5 to 15 mL of the local anesthetic/opioid solution, injected in 5-mL increments. Ten to 15 mL provides satisfactory analgesia for most nulliparous women in early labor; injection of 20 mL may be necessary if a dilute solution (e.g., 0.0625% bupivacaine) is used. A smaller dose is necessary if administered after a standard test dose.

We typically give an epinephrine-containing test dose before initiation of epidural analgesia in laboring women. Some anesthesia providers elect to omit the epidural test dose when initiating epidural labor analgesia, particularly if a woman wishes to ambulate in early labor. The omission of the epidural test dose requires that the therapeutic dose of local anesthetic be injected slowly, incrementally, and cautiously, because the therapeutic dose functions as the test dose. These precautions should be followed with all bolus injections of local anesthetic through an epidural catheter.

For nulliparous women in the active phase of the first stage of labor, CSE analgesia is usually initiated with the intrathecal injection of an opioid combined with a local anesthetic (fentanyl 15 µg and bupivacaine 2.5 mg). Alternatively, epidural analgesia can be initiated with a local anesthetic (bupivacaine 0.125%) combined with an opioid (fentanyl 100 µg). Women in active labor may require a higher total volume of epidural local anesthetic solution (15 to 20 mL) than women in early labor (10 to 15 mL) as well as a higher local anesthetic concentration (e.g., 0.125% rather than 0.0625% bupivacaine).

Labor typically progresses at a faster rate in parous women, who often require a more rapid onset of analgesia and more extensive neuroblockade than nulliparous women when neuraxial analgesia is initiated at the same cervical dilation. Therefore, in healthy parous women CSE analgesia is usually initiated with an intrathecal opioid combined with a local anesthetic, regardless of the stage and phase of labor. Alternatively, epidural analgesia is initiated with bupivacaine 0.125% combined with fentanyl 100 µg.

CSE analgesia with both a local anesthetic and an opioid is particularly advantageous for parous women in the late active phase of the first stage of labor and in all women in whom neuraxial analgesia is initiated in the second stage of labor. Sacral neuroblockade is required for complete analgesia during the second stage of labor; this neuroblockade is difficult to accomplish in a timely fashion with an initial (de novo) lumbar epidural injection of analgesic/anesthetic agents. (For initiation of lumbar epidural anesthesia in late labor, the injection of a large volume [≥ 20 mL] of local anesthetic solution may be required to achieve sacral analgesia, and this injection often results in a mid- or high-thoracic neuroblockade that is more extensive than desired. Therefore, when initiating neuraxial analgesia in late labor, a CSE technique is preferred).

Maintenance epidural analgesia is typically initiated soon after the initiation of analgesia (within 15 to 30 minutes) rather than waiting for the neuroblockade to regress. There are several advantages to this technique. Most women experience seamless analgesia (i.e., there is no window of pain as the initial block regresses). The workload for the anesthesia provider is lessened, because he or she can set up and initiate the epidural infusion while monitoring the patient for hypotension after initiation of neuroblockade. Finally, an epidural bolus of local anesthetic is not required to reestablish or extend neuroblockade, possibly enhancing safety.

Analgesia is typically maintained with a dilute solution of an amide local anesthetic and an opioid, administered by continuous infusion or PCEA. My colleagues and I prefer PCEA because it allows patient titration of neuroblockade and entails less risk for breakthrough pain. Patient satisfaction is better and the workload for the anesthesia provider is decreased. At our institution, the PCEA infusion pump parameters are the same for all laboring women, so there are fewer errors in pump setup. However, when a continuous infusion is used without PCEA to maintain analgesia, it may be necessary to titrate the continuous infusion rate to individual patient needs. For example, women in early labor require less drug to maintain analgesia (6 to 10 mL/h), whereas women in more advanced labor may require a higher infusion rate (8 to 15 mL/h). Similarly, a parous patient may require a higher infusion rate than a nulliparous patient, even though analgesia is initiated at the same stage of labor.

Some parturients experience breakthrough pain. After evaluating the nature of the pain, the extent of neuro­blockade, and the progress of labor, we usually treat breakthrough pain with a bolus epidural injection of bupivacaine 0.125%, 10 to 15 mL, administered in 5-mL increments. The patient may benefit from additional instruction about the optimal use of PCEA. Occasionally, we may elect to use a more concentrated local anesthetic solution (e.g., bupivacaine 0.25%), particularly in the presence of an abnormal fetal position or dysfunctional labor. In this case, the concentration of the maintenance solution may also need to be increased.

This maintenance technique usually results in satisfactory perineal analgesia for delivery. Occasionally, women with epidural analgesia require additional (more dense) analgesia for delivery, particularly if an instrumental vaginal delivery is planned. In this case, we often administer 5 to 12 mL of 1% to 2% lidocaine or 2% to 3% 2-chloroprocaine. This usually results in satisfactory sacral anesthesia in a patient with preexisting epidural labor analgesia.

There is no single correct way to provide neuraxial labor analgesia, although for particular patients and specific clinical conditions some methods may have advantages over others. Frequent communication among members of the anesthesia, obstetric, and nursing teams is essential to the safe and satisfactory provision of neuraxial labor analgesia. In addition, within each labor and delivery unit, consistency among anesthesia providers in their choice of techniques, specific drugs, and drug doses/concentrations is likely to result in fewer errors and higher satisfaction among other caregivers and patients.

Key Points

• Neuraxial analgesia is the most effective form of intrapartum analgesia currently available.

• In most cases, maternal request for pain relief represents a sufficient indication for the administration of neuraxial analgesia.

• The safe administration of neuraxial analgesia requires a thorough (albeit directed) preanesthetic evaluation and the immediate availability of appropriate resuscitation equipment.

• Neuraxial labor analgesia is not a generic procedure. The procedure should be tailored to individual patient needs.

• The administration of the epidural test dose should allow the anesthesia provider to recognize most cases of unintentional intravascular or intrathecal placement of the epidural catheter. All therapeutic doses of local anesthetic should be administered incrementally.

• Bupivacaine is the local anesthetic most often used for epidural analgesia during labor. Ropivacaine and levobupivacaine are satisfactory alternatives. Most anesthesia providers reserve 2-chloroprocaine and lidocaine for cases that require the rapid extension of epidural anesthesia for vaginal or cesarean delivery.

• The addition of a lipid-soluble opioid to a neuraxial local anesthetic allows the anesthesia provider to provide excellent analgesia while reducing the total dose of local anesthetic and minimizing the side effects of each agent. Perhaps the major advantage of this technique is that the severity of motor block can be minimized during labor.

• Intrathecal opioids alone may provide complete analgesia during the early first stage of labor. Epidural opioids without local anesthetics do not provide complete analgesia during labor.

• Administration of a local anesthetic (with or without an opioid) is necessary to provide complete neuraxial analgesia for the late first stage and the second stage of labor. Although a neuraxial local anesthetic alone can provide complete analgesia, the required dose is often associated with an undesirably dense degree of motor blockade.

• Hypotension is a common side effect of neuraxial analgesia. Prophylaxis and treatment involve the avoidance of aortocaval compression and the administration of a vasopressor as needed. The administration of an intravenous fluid “preload” does not significantly decrease the incidence of hypotension in euvolemic patients.

• Other potential side effects of neuraxial analgesia include pruritus, shivering, urinary retention, delayed gastric emptying, maternal fever, and fetal heart rate changes.

• Complications of neuraxial analgesia include inadequate analgesia, unintentional dural puncture, respiratory depression, unintentional intravenous injection, and extensive or total spinal anesthesia.

• The presence of severe pain during early labor—and/or an increase in local anesthetic/opioid dose requirement—may signal a higher risk for prolonged labor and operative delivery.

• Neuraxial labor analgesia is not associated with a higher rate of cesarean delivery than systemic opioid analgesia.

• Initiation of neuraxial analgesia in early labor (cervical dilation < 4 to 5 cm) does not increase the rate of cesarean delivery or prolong the duration of labor.

• Effective neuraxial analgesia likely results in a modest prolongation of the second stage of labor.

• Controversy exists as to whether there is a cause-and-effect relationship between neuraxial labor analgesia and risk for instrumental vaginal delivery. Dense neuroblockade (e.g., presence of significant motor blockade) and complete analgesia during the second stage of labor probably increase the rate of instrumental vaginal delivery. Use of a dilute solution of local anesthetic and opioid is less likely to adversely affect the progress of labor.

• Maternal-fetal factors and obstetric management—not the use of neuraxial analgesia—are the most important determinants of the cesarean delivery rate.

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* The Institute of Safe Medicine Practices (ISMP) has recommended that health care providers never use µg as an abbreviation for micrograms, but rather they should use mcg (http://www.ismp.org/tools/errorproneabbreviations.pdf, accessed February 2013). The use of the symbol µg is frequently misinterpreted and involved in harmful medication errors. The abbreviation may be mistaken for mg (milligrams), which would result in a 1000-fold overdose. The symbol µg should never be used when communicating medical information, including pharmacy and prescriber computer order entry screens, computer-generated labels, labels for drug storage bins, and medication administration records. However, most scholarly publications have continued to use the abbreviation µg. The editors have chosen to retain the use of the abbreviation µg throughout this text. However, the editors recommend the use of the abbreviation mcg in clinical practice.

* References 388, 392, 403-411, 413, 415-417, 419-423, 425-427.

* References 50, 88, 139, 141, 144, 478.

* References 107, 109, 114, 220, 221, 517.