Several changes have occurred in the past decade regarding the methods, drugs, and strategies used to provide epidural analgesia for labor. Improvements in patient satisfaction and safety have contributed to the increasing use of epidural analgesia during labor.1 Along with these advances, significant controversy has arisen about whether and how such techniques may affect the course and outcome of labor. Although regional anesthesia has been associated with a reduction in anesthesia-related maternal mortality, there is continuing controversy over whether epidural analgesia impedes the progress of labor by causing dystocia and increasing operative delivery rates.1–3 Evidence is unclear, because previous reviews have included disparate regimens for epidural analgesia and women of mixed parity.4–6 Studies investigating the effect of epidural on the duration of labor in nulliparous women have produced inconsistent results.7–9 Moreover, evidence regarding the effect of different epidural techniques on the duration of labor and mode of delivery has also been inconclusive.10–13 We sought to compare continuous epidural infusion containing fentanyl and bupivacaine with patient-controlled epidural analgesia with intermittent bolus infusion containing bupivacaine only on the duration of labor and patients’ satisfaction in nulliparous women. Moreover, we investigated the effect of epidural usage compared with other analgesia during labor regarding labor duration and outcome. To overcome the confounding effect parity may have, we selected nulliparous women only, who may be at a higher risk for dystocia.
PATIENTS AND METHODS
This study was performed in the labor and delivery ward of the department of Obstetrics and Gynecology at Ha’Emek Medical Center in Afula, Israel, a university teaching hospital affiliated with the Rappaport Faculty of Medicine of the Technion–Israel Institute of Technology, in Haifa, Israel. From January 6, 2004, to July 22, 2004, all nulliparous women at term (37 weeks or more) who requested epidural analgesia during labor were randomly allocated in a prospective study to receive either a basal continuous infusion of 0.125% bupivacaine with 2 μg/mL fentanyl at a rate of 8 mL/h with patient-controlled epidural analgesia doses of 3 mL of this solution with a lockout time of 20 minutes (group A) or intermittent bolus infusions of 10 mL of 0.25% bupivacaine on demand with minimal intervals of 60 minutes (group B). Both were continued until delivery. The epidural catheter was located at level L2/3. Blood pressure, heart rate, respiratory rate, and maternal oxygen saturation were recorded before and after each epidural injection and hourly thereafter until delivery. Patients were asked to score their pain using a 10-cm linear scale (visual analog pain score) before insertion of the epidural and hourly thereafter. A control group was the next nulliparous women admitted to our labor unit, but who chose analgesia other than epidural (group C). Alternative analgesia included 50 mg of intravenous pethidine at a 2–4-hour interval as required, inhalation of a mixture of O2 with N2O, or both. Included were nulliparous patients with singleton cephalic term pregnancies and cervical dilatation between 2 cm and 5 cm. Patients with intrauterine fetal death or a known malformed fetus were excluded. Women in the study groups were recruited before any analgesia was administered but were allowed to have analgesia other than the epidural until a dilatation of 2 cm. To prevent any crossover effect, controls that subsequently asked for epidural analgesia were excluded from the study.
The primary outcomes measured were the mean durations of the active phase of labor and the second stage of labor and patients’ satisfaction. By definition, the active phase of labor began when cervical dilatation was greater than 4 cm and ended with full cervical dilatation. The second stage of labor began with full cervical dilatation until delivery of the newborn. Patients expressed their satisfaction using a score from 1 (absolutely not satisfied) to 5 (absolutely satisfied). Secondary outcomes investigated were the mode of delivery, oxytocin usage for labor augmentation, analgesia-related complications (hypotension, itching, urinary retention, and fetal heart rate decelerations necessitating immediate operative delivery), intrapartum fever, postpartum perineal tears, postpartum hemorrhage. Neonatal outcome was measured by cord pH and Apgar score at 1 and 5 minutes. The following variables were considered: maternal age, ethnicity, educational status, gestational age at delivery, birthweight, antepartum obstetric complications (gestational diabetes, hypertension, antepartum bleeding, thrombophilia, and oligohydramnios), use of other analgesic drugs before the epidural, and whether the labor started spontaneously or after induction. Continuous electronic fetal heart rate monitoring for all groups was initiated and continued until delivery. Progress of labor was documented hourly. The protocol of oxytocin usage for induction or augmentation was 1 mU/min increased by 1 mU/min every 20 minutes. Arrest of dilatation during the active phase was determined when the Montivedeo score was above 200 for more than 2 hours. Arrest of descent was defined as an arrest of descent of the fetal head for more than 1 hour during the second stage of labor. When arrest of descent was diagnosed at a level below the midpelvis, a vacuum extraction was used, and when above the midpelvis, a cesarean delivery was performed. Women were allowed to push when they felt an urge to do so during the second stage of labor. The protocol was approved by the hospital Institutional and Governmental Review Board.
Randomization of group A and B was performed using Microsoft Excel XP Professional (Microsoft, Redmond, WA). The sequence was concealed until intervention was assigned. The allocation sequence was generated by the primary author. Attending physicians enrolled and assigned participants to their groups.
Student t test was used for comparisons of continuous variables and χ2 or Fisher exact tests were used for comparisons of categorical variables between group A and B. One-way analysis of variance was used to evaluate differences in continuous variables across the 3 groups. When a significant difference was observed, a pair-wise multiple comparison test (Bonferroni) was used for determining the difference between each pair of means. A P < .05 was considered significant. A sample size of 63 subjects in each group was needed to demonstrate a difference of 30 minutes, considered clinically significant, in duration of the second stage of labor (± 60 minutes) between groups A and B with an alpha of 0.05 and power of 80%. An intention-to-treat analysis was used.
A total of 190 patients were enrolled into this trial during the study period. All were subsequently delivered at our department (Fig. 1). None was lost to follow-up. Sixty-three were randomly assigned to receive continuous infusion and 64 received intermittent bolus infusion. Sixty-three patients who comprised the control group used a mixture of O2 and N2O, pethidine, or both. Maternal age, educational status, ethnicity, gestational age, mode of onset of labor, cervical dilatation at epidural insertion, number of augmented deliveries, birth weights, visual analog pain score reading, and number of women requiring additional analgesia other than epidural were not significantly different between groups A and B (Table 1). The mean duration of the active phase and second stage of labor did not differ between groups A and B (Table 2). Each technique produced comparable analgesia, achieving equivalent maternal satisfaction. There was no significant difference regarding the mode of delivery (Table 2). In each group, 10 women required operative delivery for arrest of dilatation or descent and for nonreassuring fetal heart rate monitoring. Among women delivered vaginally, the amount of bupivacaine 0.25% infused was significantly higher in group A (51.4 mL ± 26.6 mL) than in group B (28.5 mL ± 13.2 mL) (P < .01). Two women in group A experienced weakness in 1 leg postpartum. Of these, one had a subdural hematoma diagnosed by CT scan and was treated with corticosteroids. Both women fully recovered before discharge. No significant differences were detected between groups A and B regarding intrapartum fever, spontaneous perineal tears or postpartum hemorrhage (Table 2). Of 4 women with intrapartum fever in group A, 2 had amnionitis, of whom 1 had premature rupture of membranes. In this group 1 delivered abdominally and 3 vaginally.
When comparing groups A and B with the controls (group C), gestational age, antepartum complications, birth weights, mode of onset of labor, and number of augmented deliveries were not significantly different between the groups (Table 1). Significantly more Jewish women than Arab women chose to receive epidural. Moreover, women who chose not to receive an epidural were younger, had fewer years of formal education, and were more often homemaker (Table 1). Mean duration of the active phase was shorter among the controls than group A or B but reached statistical significance only when compared with group B (Table 2). Mean duration of the second stage of labor was significantly shorter in the control group compared with the study groups (Table 2). Mode of delivery, spontaneous perineal tears, and postpartum hemorrhage were not significantly different between the groups (Table 2).
Neonatal outcome measured by cord pH and Apgar score at 1 and 5 minutes were not significantly different between the groups. There were no cases of cord pH less than 7.20 or Apgar score less than 7 in either of the groups. No significant difference in meconium-stained amniotic fluid was detected between the groups, and neither was persistent occipitoposterior position at birth.
This study provides evidence that both continuous and intermittent epidural infusion on demand produce comparable analgesia, achieving equivalent maternal satisfaction with no difference in the duration of labor between them. Neonatal and maternal outcomes are comparable. Total use of bupivacaine, however, was higher with continuous compared with intermittent bolus infusion. Collis et al14 reported also that the total use of bupivacaine was higher with continuous infusion compared with other techniques; however, overall satisfaction was equally high.
Contradictory reports exist regarding the effect of epidural analgesia in nulliparous women regarding the duration of labor.7–9 A recent meta-analysis of patients randomly assigned to receive either epidural analgesia or parenteral opioid analgesia4 reported a prolongation of the first stage of labor by an average of 42 minutes and a prolongation of the second stage of labor by an average of 14 minutes. Liu et al15 reported similar results regarding the effect of epidural on the 2nd stage of labor, but were unable to determine whether epidural analgesia prolonged the first stage. Nevertheless, the evidence is unclear, because several reports have included disparate regimens for epidural analgesia and women of mixed parity. In this study we selected nulliparous women only, to overcome the confounding effect of parity. The active phase of labor was prolonged by an average of 60 minutes and the 2nd stage by an average of 36 minutes regardless of the type of epidural compared with controls. Although patients receiving epidural analgesia had a longer duration of labor compared with controls, this was not associated with poorer maternal or neonatal outcomes in our analysis. We found no worsening of Apgar scores or umbilical acid-base status in neonates whose mothers had received epidural analgesia. Moreover, we found no increased risk of the maternal postpartum complications, ie, postpartum hemorrhage, perineal tears, and fever.
In this study, epidural analgesia was continued through the second stage of labor. This approach is supported by a recent Cochrane report,16 which showed that stopping epidural analgesia late in labor did not produce significant differences in the incidence of spontaneous vaginal deliveries, instrumental deliveries, duration of the second stage of labor, incidence of fetal malposition at delivery or neonatal outcome compared with continuing epidural until birth. Adequate pain relief was negatively affected significantly among women whose epidurals were stopped early.16
Conflicting reports exist regarding the effect of epidural techniques on the duration of labor and mode of delivery. Driver et al10 as well as Lamont et al17 reported that continuous compared with intermittent epidural infusion reduced the risk of cesarean delivery in primiparous women. Halonen et al11 reported that compared with intermittent bolus infusion, patient-controlled epidural analgesia followed by continuous infusion was associated with prolongation of the second stage of labor, and an increased rate of cesarean delivery. Two other studies were unable to confirm that the epidural technique influenced the mode of delivery.12–13 According to our results, both the duration of labor and mode of delivery are not influenced by the epidural technique used.
Another conflicting issue is the effect of epidural analgesia compared with parenteral opioids on the mode of delivery. Liu et al15 performed a systemic review of all randomized controlled trials comparing epidural infusions with parenteral opioids. They reported that nulliparous women who receive epidural analgesia during labor do not seem to be at an increased risk of delivery by cesarean. However, epidural analgesia was associated with a higher risk of instrumental vaginal delivery. Although controls were not randomized, our analysis does not support an association between epidural analgesia and an increased risk of cesarean delivery or instrumental vaginal delivery. However, the sample size in our study was not chosen to provide power to analyze differences in operative delivery between the groups.
Finally, we found significant disparities in epidural analgesia demand between the 2 ethnic groups that composed our study population. It is important to note that anesthesiologists at our medical center are available equally to provide epidural analgesia services to all laboring women, and the medical insurance in the state of Israel covers all the costs of labor including all types of analgesia. Moreover, at our delivery ward, the providers are both Arabs and Jews, and both are capable of coping and obtaining bilingual informed consent, yet significant ethnic disparities were present. Rust et al18 found also significant racial or ethnic differences in the rates of epidural analgesia for the management of pain. Moreover, maternal age and education influenced a woman’s decision to seek epidural analgesia during labor and delivery. This is supported by our results, which showed that epidural usage was decreased among younger women and those with fewer years of formal education.
There are several possible explanations for these findings, such as personal perceptions of pain and cultural values which may dissuade some women from seeking medical interventions to control pain.19 Moreover, concern and fear of future side effects, particularly low back pain, is a major impediment to accepting epidural analgesia. This “condemned Mythos” is firmly established among our population despite recent reassuring reports.20 These differences or disparities among identically insured women require further research to ascertain possible causes. A study regarding the factors that may dissuade laboring women from using epidural analgesia to control pain during labor is currently in progress at our department.
In summary, we provide evidence that both continuous and intermittent epidural infusion on demand have comparable influence regarding the duration of labor. Additionally, each technique produced comparable analgesia, achieving equivalent maternal satisfaction. Although patients receiving epidural analgesia experienced longer labors compared with controls, the increasing use of continuous electronic fetal monitoring seems to allow for longer but more comfortable and safe labor for both mothers and neonates.
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