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The Effect of Adding a Background Infusion to Patient-Controlled Epidural Labor Analgesia on Labor, Maternal, and Neonatal Outcomes: A Systematic Review and Meta-Analysis

Heesen, Michael MD*; Böhmer, Johannes; Klöhr, Sven MD; Hofmann, Thomas MD; Rossaint, Rolf MD; Straube, Sebastian BM BCh, MA, DPhil§

doi: 10.1213/ANE.0000000000000743
Obstetric Anesthesiology: Research Report

BACKGROUND: Patient-controlled epidural analgesia (PCEA) has gained popularity, but it is still unclear whether adding a background infusion confers any benefit.

METHODS: A systematic literature search in PubMed, Embase, CINAHL, LILACS, CENTRAL, Clinicaltrials.gov, and ISI WOS was performed to identify randomized controlled double-blind trials that compare PCEA-only with PCEA combined with a continuous infusion (PCEA + CI) in parturients. The data were subjected to meta-analyses using the random-effects model. Our primary outcome was the incidence of instrumental vaginal delivery. Secondary outcomes were incidences of spontaneous vaginal and cesarean deliveries, duration of labor, analgesic outcomes, maternal outcomes (visual analog scale scores for pain, maternal satisfaction, nausea, pruritus, hypotension), and neonatal outcomes (Apgar score, umbilical artery pH).

RESULTS: We identified 7 trials with a low risk of bias, reporting on 891 parturients, for inclusion in our systematic review. The risk of instrumental vaginal delivery was increased in the PCEA + CI group, risk ratio (RR) 1.66 (95% confidence interval 1.08–2.56, P = 0.02; I2 = 0%); the RR for cesarean delivery was 0.83 (95% confidence interval 0.61–1.13, I2 = 0%). The second stage of labor was prolonged (weighted mean difference 12.3 minutes, 95% confidence interval 5.1–19.5 minutes, P = 0.0008; I2 = 0%) in the PCEA + CI group. Fewer patients in the PCEA + CI group required physician-administered boluses (RR 0.35 [95% confidence interval 0.25–0.47, P < 0.00001; I2 = 0%]). No differences regarding maternal adverse events (nausea, pruritus, hypotension) or neonatal outcomes (Apgar scores <7, umbilical artery pH) were observed.

CONCLUSIONS: On the basis of current evidence, no conclusion can be drawn regarding the risks or benefits of adding a continuous background infusion to PCEA compared with PCEA-only epidural labor analgesia. Further high-quality studies involving a sufficient number of patients are required.

Supplemental Digital Content is available in the text.Published ahead of print April 21, 2015

From the *Department of Anaesthesia, Kantonsspital Baden, Baden, Switzerland; Department of Anesthesiology, Klinikum am Bruderwald, Bamberg, Germany; Department of Anesthesiology, University Hospital Aachen, Aachen, Germany; and §Division of Preventive Medicine, University of Alberta, Edmonton, Alberta, Canada.

Accepted for publication January 8, 2015.

Published ahead of print April 21, 2015

Funding: Only departmental funds.

The authors declare no conflicts of interest.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website.

Reprints will not be available from the authors.

Address correspondence to Michael Heesen, MD, Department of Anesthesiology, Klinikum am Bruderwald, Bugerstr. 80, 96049 Bamberg, Germany. Address e-mail to michael.heesen@ksb.ch.

Labor epidural analgesia can be delivered as a continuous infusion (CI), by a bolus technique or by patient-controlled epidural analgesia (PCEA). The latter was developed to allow the parturient to self-administer a bolus and thereby reduce the time between the onset of pain and the administration of additional analgesia. PCEA was found to be associated with less motor block, less local anesthetic consumption, and a lower frequency of clinician top-ups than CI.1 Other clinicians, however, chose to add CI to a bolus technique,2–4 but it remains unclear whether the combination of both techniques confers benefits. A systematic review5 identified some advantages of a background infusion including fewer unscheduled anesthetic interventions, but this finding was based on only 2 studies. A meta-analysis gathering all available evidence is therefore needed.6 To guide clinical practice, we conducted a systematic review and a meta-analysis of high-quality, randomized controlled double-blind trials. Our primary outcome parameter was the rate of instrumental deliveries. Further outcome variables were rates of spontaneous vaginal and cesarean deliveries, duration of labor, and analgesic, maternal, and neonatal outcomes.

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METHODS

A systematic literature search was conducted in the databases PubMed, Embase, CINAHL, LILACS, CENTRAL, Clinicaltrials.gov, and ISI WOS from inception to November 1, 2014, using the following search terms: (epidural[All Fields] AND (“labour”[All Fields] OR “labor, obstetric”[MeSH Terms] OR (“labor”[All Fields] AND “obstetric”[All Fields]) OR “obstetric labor”[All Fields])) AND ((background[All Fields] AND infusion[All Fields]) OR (basal[All Fields] AND infusion[All Fields]) OR (continuous[All Fields] AND infusion[All Fields])) AND (patient-controlled epidural OR patient controlled epidural OR patient-controlled peridural OR patient controlled peridural OR self-administered epidural OR self administered epidural OR self-administered peridural OR self administered peridural). No filter regarding language or type of publication was applied. The reference lists of retrieved studies were also screened to identify additional articles. Two authors (MH, SK) performed the searches independently; a third party (SS) would have been involved if disagreements could not be resolved by discussion. Double-blind, randomized controlled trials (RCTs) comparing PCEA combined with a continuous (basal) infusion with PCEA-only were eligible for inclusion in our systematic review.

Based on guidance developed by the Cochrane Collaboration,7 methodological study quality was scored in duplicate (MH, JB) as adequate, unclear, or inadequate, as determined by the risk of bias in the following domains: selection bias (random sequence generation, allocation concealment), performance bias (blinding of participant and personnel), and detection bias (blinding of assessor). To be included, a trial had to meet the following criteria:

  1. adequate method of randomization (scored as “yes”; Table 1),
  2. blinding of patient and outcome assessor (these 2 domains had to be scored “yes”), and
  3. at least 6 of the 12 domains that we assessed had to be scored as “yes.”
Table 1

Table 1

Our systematic review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement.8

Our primary outcome was the incidence of instrumental vaginal delivery. Secondary outcomes included obstetric outcomes (incidences of spontaneous vaginal and cesarean deliveries, duration of labor), analgesic outcomes (consumption of ropivacaine equivalents, physician-delivered boluses, PCEA-delivered boluses, motor weakness), maternal outcomes (visual analog scale [VAS] scores for pain, maternal satisfaction, nausea, pruritus, hypotension), and neonatal outcomes (Apgar score, umbilical artery pH).

When reported, means and SDs were extracted; if only the SEM was reported, we calculated the SD by multiplying the SEM with the square root of the number of patients in the group. Mean and SD were derived from median and range (minimum–maximum) by the formula reported by Hozo and colleagues.9 Standard error was calculated from a 95% confidence interval by dividing the difference of the upper minus the lower limit by 3.92, according to the Cochrane Handbook for Systematic Reviews of Interventions, chapter 7.7.7.2.10

We calculated ropivacaine equivalents (mg); ropivacaine and levobupivacaine were assumed to have a relative potency of 60% compared with bupivacaine.11,12

If 2 or more PCEA-only groups were studied in a report, we combined these data. This was done by simple addition for dichotomous variables; for continuous variables, we applied the formulae from the Cochrane Handbook.10

Review Manager (RevMan, version 5.1, The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, 2008) was used for meta-analysis. Use of a random-effects model was planned a priori because of clinical and methodological heterogeneity among studies. Pooled RR and 95% confidence intervals were calculated for dichotomous variables, and weighted mean differences (WMDs) for pooled continuous data. P values <0.05 indicated statistical significance. The I2 statistic is reported as a measure of heterogeneity with I2 values >50% indicating significant heterogeneity. Funnel plots were performed to assess publication bias.

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RESULTS

Our literature search identified 337 studies (Fig. 1); the full text of 16 articles was assessed in detail. Three studies13–15 did not compare PCEA + CI with PCEA-only; thus, 13 studies were scored for methodological quality. The methodology quality scores are described in Table 1. Six studies2,16–20 were excluded for methodological reasons. Seven studies21–27 were considered eligible for inclusion; these reported on 891 subjects. There was no disagreement between the 2 investigators who screened the studies. Details of these trials, including a description of the epidural technique and inclusion and exclusion criteria, are shown in Table 2.

Table 2

Table 2

Figure 1

Figure 1

The rate of instrumental vaginal deliveries was higher in patients in the PCEA + CI group compared with the PCEA-only group (RR = 1.66, 95% confidence interval 1.08–2.56, P = 0.02; I2 = 0%, P = 0.96) (Fig. 2A). The RR for cesarean delivery was 0.83 (95% confidence interval 0.61–1.13, P = 0.23; I2 = 0%) (Fig. 2B). We did not find an association between the epidural maintenance regimen and the rate of spontaneous vaginal deliveries (Fig. 2C).

Figure 2

Figure 2

The total duration of labor and the duration of the first stage of labor did not differ between the groups (Fig. 3); however, there was significant heterogeneity in the analysis of first stage of labor. The second stage of labor was prolonged in the PCEA + CI groups (WMD 12.3 minutes, 95% confidence interval 5.1–19.5, P = 0.0008; I2 = 0%, P = 0.55) compared with the PCEA-only group.

Figure 3

Figure 3

The total ropivacaine-equivalent consumption was higher in the PCEA + CI group; the WMD was 18.0 mg (95% confidence interval 1.4–34.5, P = 0.03; I2 = 92%, P< 0.00001) (Fig. 4A). The rate of patients requiring physician-administered boluses was significantly lower in the PCEA + CI group (RR 0.35, 95% confidence interval 0.25–0.47, P < 0.00001; I2 = 0%, P = 0.92) (Fig. 4B). The number of episodes of breakthrough pain was reported in 2 studies,23,27 both finding a lower incidence in the PCEA + CI group. The number of patient-administered PCEA boluses was lower in the PCEA + CI compared with the PCEA-only group (Fig. 4C). No significant difference was found for the number of demand PCEA boluses based on 2 studies.24,27

Figure 4

Figure 4

There was significant heterogeneity among studies regarding timing of VAS scoring and the assessment of average or maximal VAS values. We therefore report the results qualitatively. In our analysis, no differences in VAS pain scores between the 2 treatment arms were seen in 5 studies.21–24,26 In the study by Lim et al.,25 the incidence of breakthrough pain and the maximal pain scores were higher in the PCEA-only group. One report27 observed more pain with second stage pushing in the PCEA-only group.

Maternal satisfaction was assessed in 6 studies22–27; the definition and assessment of this variable was not consistent among the trials. No trial reported a difference between the treatment arms.

The number of patients with no motor weakness was reported in 3 studies22–24 and did not differ between the groups (RR 0.98, 95% confidence interval 0.92–1.06, P = 0.64).

Tables 3 and 4 show maternal and neonatal outcomes, without evidence of differences between groups. Funnel plots are shown in the Supplemental Digital Content (http://links.lww.com/AA/B124); they were not indicative of publication bias on visual inspection.

Table 3

Table 3

Table 4

Table 4

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DISCUSSION

The important finding of our systematic review and meta-analysis was an increased risk for instrumental vaginal delivery in patients who used PCEA with a continuous background infusion compared with PCEA alone for maintenance of epidural labor analgesia. Although the risk for cesarean delivery was not different between the 2 groups, the confidence interval for the relative risk of cesarean delivery was wide and included a clinically significant difference.

The relative risks we calculated for instrumental vaginal and cesarean deliveries demonstrated different directions of effect. This discrepancy may be due to the low number of patients included in the analysis. Our risk estimate for instrumental vaginal delivery was heavily influenced by 1 study10; all other studies crossed the line of no effect with fairly large confidence intervals.

The addition of a background infusion to PCEA also led to a prolonged duration of the second stage of labor by approximately 12 minutes; the clinical significance of this prolongation is unclear. The rate of patients requiring physician-delivered boluses was lower when PCEA was combined with a CI; the number of PCEA boluses was also lower in this treatment arm. The consumption of ropivacaine equivalents was higher in the PCEA + CI group than in the PCEA-only group, but there was significant heterogeneity among studies.

One would expect that higher local anesthetic consumption would result in a greater incidence of motor block, but pooling of data from the studies we reviewed showed no difference in the number of patients with no motor weakness. In vitro studies28 show that a constant infusion leads to higher extraneural levels of local anesthetics than intermittent boluses, which allow extraneural levels to decline in the interval between 2 boluses. The high extraneural concentration of local anesthetics may cause high intraneural concentration, and these levels may become sufficiently high to cause motor blockade. There are several possible reasons that could explain our finding no differences in motor weakness when adding a background infusion to PCEA. First, there may be subtle changes in the degree of motor block that were not assessed. Second, the weakness or block of peripheral muscles, usually of the lower limb, may not correlate with the effect on muscles involved in childbirth. Third, despite differences between groups, the amount of drug may be too low to cause a motor block, even in the higher-dose group. Some support for this hypothesis comes from a meta-analysis that compared continuous epidural infusions with PCEA-only.1 The trials included in that meta-analysis also reported on the number of parturients without motor weakness and found a higher percentage in the PCEA-only group. The risk for instrumental vaginal delivery, however, was not increased, suggesting that there may be no association between instrumental delivery and motor block.

In a 2009 systematic review, Halpern and Carvalho5 stated that a background infusion reduced “the number of unscheduled clinician interventions.” We came to the same conclusion when pooling the data reported in the studies of our analysis. The 2007 Practice Guidelines for Obstetric Anesthesia of the American Society of Anesthesiologists Task Force on Obstetric Anesthesia29 also addressed the comparison of PCEA-only with PCEA + CI and included 5 studies17,18,21–23 in a meta-analysis. Of these studies, we excluded reports by Petry et al.17 and Bremerich et al.18 because in both of these studies the outcome assessors were not blinded, and thus were prone to detection bias. In addition to the studies21–23 evaluated in the ASA Practice Guidelines29 we analyzed 4 additional high-quality studies24–27 that contributed 635 patients to our analysis. The ASA Practice Guidelines29 found significantly better pain relief in women who received PCEA + CI compared with PCEA-only, whereas no significant differences were observed for spontaneous delivery and motor block between PCEA-only and PCEA + CI. In 225,27 of the 7 studies included in our analysis, higher pain scores were observed in the PCEA-only group, whereas 5 reports21–24,26 did not find significant differences. Our results are similar to those of the ASA Practice Guidelines29 regarding motor block and incidence of spontaneous delivery.

There are some limitations to our systematic review. Heterogeneity among studies in our analysis could have been caused by differences in techniques among studies, including the concentration of the local anesthetic used in the study arms, early versus late initiation of epidural analgesia, and initiation of analgesia with a combined spinal-epidural versus a traditional epidural analgesia technique. In a recent meta-analysis, Sultan et al.30 showed that low concentrations of local anesthetics for labor epidural analgesia reduce the risk for instrumental vaginal delivery compared with high concentration solutions. Bupivacaine concentrations below 0.1% and ropivacaine below 0.17% were considered low in this context. Of the studies in our review, 6 trials used a concentration that met the above definition. The trial by Ferrante et al.21 administered 0.125% bupivacaine. The concentration of the local anesthetic, therefore, is unlikely to have a major impact on the association between CI and the risk of instrumental vaginal delivery in our meta-analysis. Because low-concentration solutions are now the norm, the conclusion from our meta-analysis appears generalizable to current practice.

Another parameter that varied among studies included in our analysis is the timing of the initiation of labor analgesia. Early initiation was performed in 2 studies,21,26 and at a cervical dilation of <5 cm in the study by Lim et al.25 Women at >5 cm cervical dilation were excluded in the study by Haydon and colleagues.27 No details were given in 3 studies.22–24 The effect of the type of neuraxial analgesia should also be considered. Combined spinal-epidural (CSE) analgesia was used in 3 studies23,25,27 and epidural analgesia in 4 studies included in our meta-analysis. A Cochrane review meta-analysis31 found a lower incidence of assisted vaginal delivery in women randomly assigned to receive CSE analgesia compared with traditional (high-dose) epidural analgesia, but CSE analgesia did not perform better compared with low-dose epidural regimens. A further limitation of our review was that not all included studies reported on all outcome variables of interest.

The current ASA Practice Guidelines29 do not provide the clinician with a clear conclusion as to whether PCEA should be combined with a CI. Our results found a decreased risk for instrumental vaginal delivery in the PCEA-only group, but we cannot exclude that this was at the expense of an increased risk for cesarean delivery. This finding thus emphasizes the need for further studies sufficiently powered to detect differences in the incidence of cesarean delivery before definite recommendations on the use of a continuous background infusion in combination with PCEA can be made.

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DISCLOSURES

Name: Michael Heesen, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Michael Heesen approved the final manuscript.

Name: Johannes Böhmer.

Contribution: This author helped conduct the study, analyze the data, and write the manuscript.

Attestation: Johannes Böhmer approved the final manuscript.

Name: Sven Klöhr, MD.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: Sven Klöhr approved the final manuscript.

Name: Thomas Hofmann, MD.

Contribution: This author helped conduct the study, analyze the data, and write the manuscript.

Attestation: Thomas Hofmann approved the final manuscript.

Name: Rolf Rossaint, MD.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: Rolf Rossaint approved the final manuscript.

Name: Sebastian Straube, BM BCh, MA, DPhil.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Sebastian Straube approved the final manuscript.

This manuscript was handled by: Cynthia A. Wong, MD.

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REFERENCES

1. van der Vyver M, Halpern S, Joseph G. Patient-controlled epidural analgesia versus continuous infusion for labour analgesia: a meta-analysis. Br J Anaesth. 2002;89:459–65
2. Paech MJ. Patient-controlled epidural analgesia in labour–is a continuous infusion of benefit? Anaesth Intensive Care. 1992;20:15–20
3. Lysak SZ, Eisenach JC, Dobson CE 2nd.. Patient-controlled epidural analgesia during labor: a comparison of three solutions with a continuous infusion control. Anesthesiology. 1990;72:44–9
4. Viscomi C, Eisenach JC. Patient-controlled epidural analgesia during labor. Obstet Gynecol. 1991;77:348–51
5. Halpern SH, Carvalho B. Patient-controlled epidural analgesia for labor. Anesth Analg. 2009;108:921–8
6. Loubert C, Hinova A, Fernando R. Update on modern neuraxial analgesia in labour: a review of the literature of the last 5 years. Anaesthesia. 2011;66:191–212
7. Furlan AD, Pennick V, Bombardier C, van Tulder MEditorial Board, Cochrane Back Review Group. . 2009 updated method guidelines for systematic reviews in the Cochrane Back Review Group. Spine (Phila Pa 1976). 2009;34:1929–41
8. Moher D, Liberati A, Tetzlaff J, Altman DGPRISMA Group. . Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. BMJ. 2009;339:b2535
9. Hozo SP, Djulbegovic B, Hozo I. Estimating the mean and variance from the median, range, and the size of a sample. BMC Med Res Methodol. 2005;20:5–13
10. Higgins JPT, Green S Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011].
11. Capogna G, Celleno D, Fusco P, Lyons G, Columb M. Relative potencies of bupivacaine and ropivacaine for analgesia in labour. Br J Anaesth. 1999;82:371–3
12. Polley LS, Columb MO, Naughton NN, Wagner DS, van de Ven CJ, Goralski KH. Relative analgesic potencies of levobupivacaine and ropivacaine for epidural analgesia in labor. Anesthesiology. 2003;99:1354–8
13. Gaiser RR, Lewin SB, Cheek TG, Gutsche BB. Effects of immediately initiating an epidural infusion in the combined spinal and epidural technique in nulliparous parturients. Reg Anesth Pain Med. 2000;25:223–7
14. Capogna G, Camorcia M, Stirparo S, Farcomeni A. Programmed intermittent epidural bolus versus continuous epidural infusion for labor analgesia: the effects on maternal motor function and labor outcome. A randomized double-blind study in nulliparous women. Anesth Analg. 2011;113:826–31
15. Saroj S, Ankita S, Uma S. Low dose epidural analgesia during labor: comparison between patient controlled epidural analgesia with basal continuous infusion and intermittent bolus technique. J Obstet Gynaecol India. 2011;61:404–7
16. Gambling DR, Yu P, Cole C, McMorland GH, Palmer L. A comparative study of patient controlled epidural analgesia (PCEA) and continuous infusion epidural analgesia (CIEA) during labour. Can J Anaesth. 1988;35:249–54
17. Petry J, Vercauteren M, Van Mol I, Van Houwe P, Adriaensen HA. Epidural PCA with bupivacaine 0.125%, sufentanil 0.75 microgram and epinephrine 1/800.000 for labor analgesia: is a background infusion beneficial? Acta Anaesthesiol Belg. 2000;51:163–6
18. Bremerich DH, Waibel HJ, Mierdl S, Meininger D, Byhahn C, Zwissler BC, Ackermann HH. Comparison of continuous background infusion plus demand dose and demand-only parturient-controlled epidural analgesia (PCEA) using ropivacaine combined with sufentanil for labor and delivery. Int J Obstet Anesth. 2005;14:114–20
19. Okutomi T, Saito M, Mochizuki J, Amano K, Hoka S. A double-blind randomized controlled trial of patient-controlled epidural analgesia with or without a background infusion following initial spinal analgesia for labor pain. Int J Obstet Anesth. 2009;18:28–32
20. Srivastava U, Gupta A, Saxena S, Kumar A, Singh S, Saraswat N, Mishra AR, Kannaujia A, Mishra S. Patient controlled epidural analgesia during labour: effect of addition of background infusion on quality of analgesia & maternal satisfaction. Indian J Anaesth. 2009;53:649–53
21. Ferrante FM, Rosinia FA, Gordon C, Datta S. The role of continuous background infusions in patient-controlled epidural analgesia for labor and delivery. Anesth Analg. 1994;79:80–4
22. Boselli E, Debon R, Cimino Y, Rimmelé T, Allaouchiche B, Chassard D. Background infusion is not beneficial during labor patient-controlled analgesia with 0.1% ropivacaine plus 0.5 microg/ml sufentanil. Anesthesiology. 2004;100:968–72
23. Missant C, Teunkenst A, Vandermeersch E, Van de Velde M. Patient-controlled epidural analgesia following combined spinal-epidural analgesia in labour: the effects of adding a continuous epidural infusion. Anaesth Intensive Care. 2005;33:452–6
24. Vallejo MC, Ramesh V, Phelps AL, Sah N. Epidural labor analgesia: continuous infusion versus patient-controlled epidural analgesia with background infusion versus without a background infusion. J Pain. 2007;8:970–5
25. Lim Y, Ocampo CE, Supandji M, Teoh WH, Sia AT. A randomized controlled trial of three patient-controlled epidural analgesia regimens for labor. Anesth Analg. 2008;107:1968–72
26. Brogly N, Schiraldi R, Vazquez B, Perez J, Guasch E, Gilsanz F. A randomized control trial of patient-controlled epidural analgesia (PCEA) with and without a background infusion using levobupivacaine and fentanyl. Minerva Anestesiol. 2011;77:1149–54
27. Haydon ML, Larson D, Reed E, Shrivastava VK, Preslicka CW, Nageotte MP. Obstetric outcomes and maternal satisfaction in nulliparous women using patient-controlled epidural analgesia. Am J Obstet Gynecol. 2011;205:271.e1–6
28. De Jong RHDe Jong RH. Dynamics of nerve block. In: Local Anesthetics. 1994 St Louis Mosby:230–45
29. American Society of Anesthesiologists Task Force on Obstetric Anesthesia. . Practice guidelines for obstetric anesthesia: an updated report by the American Society of Anesthesiologists Task Force on Obstetric Anesthesia. Anesthesiology. 2007;106:843–63
30. Sultan P, Murphy C, Halpern S, Carvalho B. The effect of low concentrations versus high concentrations of local anesthetics for labour analgesia on obstetric and anesthetic outcomes: a meta-analysis. Can J Anaesth. 2013;60:840–54
31. Simmons SW, Taghizadeh N, Dennis AT, Hughes D, Cyna AM. Combined spinal-epidural versus epidural analgesia in labour. Cochrane Database Syst Rev. 2012;10:CD003401

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