|Year : 2013 | Volume
| Issue : 3 | Page : 147-153
A randomized, double-blind, controlled study comparing Bupivacaine 0.125% and Ropivacaine 0.125%, both with Fentanyl 2 μg/ml, for labor epidural analgesia
Snigdha Paddalwar1, Manda Nagrale2, Aruna Chandak2, Deepti Shrivastava3, Juhi Papalkar3
1 Department of Cardiac Anesthesiology, Jawaharlal Nehru Medical College, Datta Meghe Institute of Medical Sciences, Wardha, Maharashtra, India
2 Department of Anesthesiology, Jawaharlal Nehru Medical College, Datta Meghe Institute of Medical Sciences, Wardha, Maharashtra, India
3 Department of Obstetrics and Gynecology, Jawaharlal Nehru Medical College, Datta Meghe Institute of Medical Sciences, Wardha, Maharashtra, India
|Date of Web Publication||7-Jan-2014|
Department of Cardiac Anesthesiology, Jawaharlal Nehru Medical College, DMIMS, Wardha- 442 001, Maharashtra
Source of Support: None, Conflict of Interest: None
Objective: A prospective, randomized, double-blind study was conducted to compare the efficacy of Ropivacaine 0.125% and Bupivacaine 0.125%, both with Fentanyl 2 microgm/ml, in labor epidural analgesia and their effect on duration and course of labor. Background: Ropivacaine was introduced as S-enantiomer. In various human and animal studies, it was found to be less cardiotoxic and has high sensory:motor differential blocking property. Both these characteristics are beneficial for labor epidural analgesia. Materials and Methods: Sixty pregnant women of ASA grade I and II, who were primigravida or multigravida, with singleton vertex presentation in established labor were randomly selected and divided into two groups of 30 each. Group R patients received Ropivacaine 0.125% with Fentanyl 2 μg/ml and group B patients received Bupivacaine 0.125% with Fentanyl 2 μg/ml as intermittent bolus doses epidurally. After taking consent from them, epidural catheter was placed in L2-3/3-4 space, followed by administration of study drugs given as top-up doses intermittently. Maternal heart rate, systolic blood pressure (SBP), Visual Analogue Scale (VAS) score, fetal heart rate (FHR), Bromage score, level of sensory analgesia, APGAR score at 1 and 5 min, and duration of labor were recorded. Results: The groups were similar in demographic attributes and obstetric variables. Ropivacaine showed no difference in the mean VAS scores and the quality of analgesia, as compared to Bupivacaine. At 20 min, all the patients in both groups were absolutely pain free with the VAS score of 0. No patient in group R developed motor block, whereas five patients in group B developed grade 2 (mild) motor block. APGAR scores were comparable in both the groups. Conclusion: We conclude that Ropivacaine is equipotent, produces less motor block, has no adverse effect on the course and duration of labor, and can be used safely.
Keywords: Analgesia, Bupivacaine, labor epidural, Ropivacaine
|How to cite this article:|
Paddalwar S, Nagrale M, Chandak A, Shrivastava D, Papalkar J. A randomized, double-blind, controlled study comparing Bupivacaine 0.125% and Ropivacaine 0.125%, both with Fentanyl 2 μg/ml, for labor epidural analgesia. Indian J Pain 2013;27:147-53
|How to cite this URL:|
Paddalwar S, Nagrale M, Chandak A, Shrivastava D, Papalkar J. A randomized, double-blind, controlled study comparing Bupivacaine 0.125% and Ropivacaine 0.125%, both with Fentanyl 2 μg/ml, for labor epidural analgesia. Indian J Pain [serial online] 2013 [cited 2019 Nov 19];27:147-53. Available from: http://www.indianjpain.org/text.asp?2013/27/3/147/124599
| Introduction|| |
Of all labor analgesic techniques, epidural analgesia is the most effective form of analgesia and has become the "gold standard" in obstetric care. Bupivacaine is commonly used for labor epidural analgesia because of its long duration of action and relative motor-sparing effect when compared with other local anesthetics. 
Ropivacaine, a newer local anesthetic released in 1996, has similar pharmacokinetic and pharmacodynamic properties as Bupivacaine. This newer local anesthetic confers less lower-extremity motor block than Bupivacaine after epidural administration, which may be advantageous. ,, Increasing motor block to the perineal or abdominal muscles from epidural local anesthetic may interfere with normal internal rotation of the fetal head,  whereas minimizing motor block during labor may allow for normal progression of labor that may translate into fewer instrumental deliveries and more vaginal deliveries,  although this is controversial.  A number of clinical labor studies comparing Ropivacaine and Bupivacaine in 0.2-0.25% concentrations have demonstrated difference in motor block between these drugs. ,
Ropivacaine has been introduced into obstetric anesthetic practice with the proposed advantage of causing less motor block compared with Bupivacaine, but it is unclear whether Ropivacaine is associated with any clinical benefit, particularly with regard to obstetric outcome.
In 1998, Writer et al, published a prospective meta-analysis that showed a greater frequency of spontaneous vaginal delivery and a smaller incidence of instrumental delivery with Ropivacaine 0.25% compared to Bupivacaine 0.25%. Ropivacaine has also gained much popularity for obstetric analgesia due to its reduced propensity for causing cardiotoxicity. , Hence, we conducted this study to compare equal concentrations of both the drugs Ropivacaine and Bupivacaine, combined with Fentanyl, for labor analgesia when given as intermittent top-up doses in a population.
| Materials and Methods|| |
After obtaining approval from the Institutional Ethics Committee, 60 nulliparous as well as multiparous women of ASA status I and II, belonging to age group of 20-30 years with full-term singleton vertex presentation, previous normal vaginal delivery, normal fetal heart rate pattern, and cervical dilatation of 3-5 cm were included in the study. Patients with coagulopathy, deformity of the spine, allergy to the study drug, and those who showed unwillingness to participate in the study were excluded. Patients were divided into two groups of 30 each, group R (Ropivacaine) and group B (Bupivacaine). Once the women were enrolled in the study, a written informed consent was obtained from them and randomization was done by asking the patient to select a sealed envelope which had code for either of the drugs. After confirming the active first stage of labor, the vital parameters were recorded, and the patient was preloaded with Ringer's lactate 10 ml/kg, epidural space was identified in L2-3/L3-4 interspinous space with epidural needle 16/18 G; using loss of resistance to air, a multi-orifice epidural catheter was inserted. An initial bolus of 10 ml of drug solution (0.125%) was given in two aliquots after giving a test dose of 3 ml of 2% lignocaine with adrenaline. After giving the test dose, the patient was monitored closely for increase in pulse rate. If there was any increase in pulse rate by more than 20% of baseline in the absence of uterine contraction and if the patient complained of feeling dizzy, tinnitus, and having metallic taste in the mouth, it was considered as intravascular drug injection. Intrathecal spread was ruled out by absence of inability to move the lower limbs and fall in blood pressure by more than 20% of baseline immediately after the test dose. Both the study drugs are available as 0.5% solutions. To prepare the study drug solution, 2.5 ml of drug was drawn into a 10 ml syringe and was diluted with normal saline up to 10 ml; this made a concentration of 0.125% and 20 μg of Fentanyl was added to this solution. Volume of drug boluses was selected based on the demographic profile of the Indian parturients. Maternal pulse rate, blood pressure, SpO2, fetal heart rate, Visual Analogue Scale (VAS) score, and degree of motor block using Bromage score [Annexure 1] [Additional file 1] were evaluated every 5 min for half an hour and thereafter every 30 min. Subsequent top-up doses were given after assessing pain relief (VAS score and subjective description by mother as excellent/good/fair/poor). Patient was assessed at 30 min intervals for pain relief, level of sensory analgesia, maternal hemodynamics, fetal heart rate, and motor block. Quality of analgesia, duration of first and second stages of labor, incidence of cesarean section, instrumental delivery, complications, side effects (sedation, nausea, and vomiting, itching, urinary retention), and occurrence of motor block were studied. During the first stage, sitting in bed or walking with assistance was allowed after performing Straight Leg Raising test and Romberg's test. When VAS was more than 4, a bolus of 5-10 ml of drug solution was given depending on the number of segments receded. For the second stage, parturients were made to lie in lithotomy position with head up and a top-up dose of 5-10 ml of the drug solution was given. Throughout the course of labor, the patients were monitored for tinnitus, metallic taste in mouth, and dizziness, as catheter migration leading to intravascular drug delivery is a known complication. After delivery, the epidural catheter was removed and duration of the second stage noted. Neonatal APGAR scores at 1 and 5 min were recorded. Parturients were interviewed a day after delivery for satisfaction level, backache, and willingness for labor epidural analgesia for subsequent pregnancy. Obstetrician's experience was also recorded after the delivery. Results were statistically analyzed using Student's t-test.
| Results|| |
Sixty patients completed the study. Thirty patients received 0.125% Bupivacaine with Fentanyl 2 mg/ml and the remaining 30 received 0.125% Ropivacaine with Fentanyl 2 mg/ml. Demographic and obstetric variables in both the groups were comparable [Table 1]. The statistical difference between the two groups was insignificant. Duration of stages I and II of labor and total duration in both the groups were comparable and showed no statistical significance; P value was >0.01 by independent t-test with equal variance [Table 2]. The mean duration of first stage of labor was 162.8 ± 43.23 min in the Ropivacaine group and 158.4 ± 39.02 min in the Bupivacaine group. As the P value was 0.710, it was statistically insignificant. The mean duration of second stage of labor in the Ropivacaine group was 33.33 ± 12.39 min and in the Bupivacaine group was 27.57 ± 16.08 min. This was statistically insignificant as the P value was 0.125. There was no statistically significant difference in the total duration of labor between the two groups, which was 196.07 ± 42.32 min and 186.33 ± 43.67 min in the Ropivacaine and Bupivacaine groups, respectively (P value 0.380).
|Table 1: Comparison of age and anthropometric variables of mothers between the two groups|
Click here to view
Maternal heart rate, blood pressure [Table 3] and [Table 4], and fetal heart rate [Figure 1] were comparable in both the groups. None of the patients had hypotension, bradycardia, and fetal bradycardia. The mean baseline VAS score in group R was 9.60 ± 0.968, whereas in group B, it was 9.17 ± 0.98 (P value 0.09, which was not significant). At 20 min, all the patients in both the groups were pain free with a VAS score of 0-2. Distribution of VAS at various intervals in both the groups was comparable and showed no statistical significance (P > 0.01) [Figure 2]. No patient out of 30 patients in group R developed motor block, whereas 5 patients in group B developed grade 2 (mild) motor block, which means the ability to weakly flex the knees (Bromage Scale) [Table 5]. The P value was 0.02, which was statistically significant, although the degree of block was mild. Twenty-three patients in group R desired to ambulate and were allowed to walk with assistance satisfactorily. Twenty-one patients in group B desired to ambulate and, hence, were made to walk satisfactorily. Distribution of Bromage scoring in both the groups showed statistical significance (P < 0.05). No patient in group R required either forceps delivery or cesarean section. In group B, there was one delivery by outlet forceps (3.33%) due to prolonged second stage. One patient required cesarean section in group B. Pattern of mode of delivery in both the groups was comparable and showed no statistical significance (P > 0.05). The mean total dose of drug required for group R was 31.83 ± 0.52 mg and for group B was 33.25 ± 7.66 mg (P = 0.444). The statistical difference between the two groups was insignificant. The mean total dose of Fentanyl in group R was 50.87 ± 10.35 μg, whereas it was 53.20 ± 12.26 μg in group B (P value 0.429, not significant).
|Table 5: Distribution of patients according to the Bromage Scale in the two groups|
Click here to view
|Figure 1: Comparison of fetal heart rate at various intervals between the two groups|
Click here to view
|Figure 2: Comparison of visual analogue scale at various intervals between the two groups|
Click here to view
There were two patients, one from each group, who had pruritus. One patient from group B had vomiting. One patient had unilateral sensory block and one patient had dural puncture; both patients were excluded from the study. Two neonates, one from each group, were admitted to Neonatal Intensive Care Unit for observation, but both were discharged after 2 h. Adverse events in both the groups [Table 6] were comparable and showed no statistical significance (P > 0.05 by chi-square test).
|Table 6: Comparison of adverse events between the two groups (cross-tabulation)|
Click here to view
Augmentation of labor in both the groups was comparable and was done as per the obstetrician's protocol for active labor management. Mean APGAR score at 1 min was 8.6 ± 0.56 in both the groups, whereas it was 8.97 ± 0.18 in group R and 9.00 ± 0.00 in group B at 5 min.
| Discussion|| |
In our study, while comparing small concentrations of Ropivacaine and Bupivacaine (both combined with Fentanyl), we found no difference in the analgesic potency, mode of delivery, and effect on duration of labor, although the incidence of motor block was more in the Bupivacaine group, which was statistically insignificant.
Most clinical studies have found epidural Ropivacaine and Bupivacaine, with or without opioids, to be similar when compared at equal concentrations ranging from 0.125 to 0.25% for maintenance of labor analgesia. ,,, Owen et al, observed similar mean hourly use of either 0.125% Bupivacaine or Ropivacaine alone, when administered by continuous infusion or by patient-controlled analgesia. The same authors  also found no statistically significant differences in the amount of local anesthetic used and verbal pain scores while using 0.075% Ropivacaine and 0.075% Bupivacaine with Fentanyl 2 μg/ml.
Meister et al, administered 0.125% Ropivacaine and 0.125% Bupivacaine with Fentanyl 2 μg/ml for labor analgesia and found both the drugs equipotent as demonstrated by mean hourly drug use, sensory levels to pin prick, and overall patient satisfaction. The results are consistent with our study results, although the mode of drug delivery was different. As there was no difference in the pain scores between the groups, this indirectly suggests that there was no important difference in the potency of the solutions used, which was also observed in other studies, ,, although the duration of analgesia was more in Ropivacaine group, which can be attributed to its intrinsic vasoconstrictor property (an added advantage of using Ropivacaine).
Whether epidural analgesia has adverse effects on the progress and outcome of labor has been the topic of much debate.  One of the factors implicated in the association between epidural analgesia and increased rates of operative delivery is motor block from the epidural local anesthetic. This may decrease maternal mobility, reduce maternal effort in the second stage, and may also predispose to inadequate rotation of the fetal presenting part secondary to relaxation of pelvic floor muscles. , All of these factors may potentially contribute to an increased requirement for operative vaginal or cesarean delivery. Motor block from local anesthetic can be minimized either by reducing the concentration of the local anesthetic or by choosing a local anesthetic with a high differential sensory:motor block ratio, such as Ropivacaine ,, The advantage of using a small concentration of local anesthetic was well demonstrated in Comparative Obstetric Mobile Epidural Trial (COMET).  This showed that the instrumental vaginal delivery rate was less frequent when a small-dose epidural regimen (Bupivacaine 0.1% with Fentanyl 0.0002%) was compared with a traditional epidural regimen (Bupivacaine 0.25%).
The advantage of using Ropivacaine is more controversial. Capogna et al and Linda et al, have found ropivaciane less potent than Bupivacaine by a factor of 0.4. Some clinical studies have shown that Ropivacaine provided analgesia with less motor block compared with similar concentrations of Bupivacaine,  similar to the findings of our study. This supports the in vitro data showing that Ropivacaine produced less block of motor A-fibers for a similar degree of block of nociceptive C-fibers, although other studies found the incidence of motor block to be similar. ,, Writer et al,  reported a prospective meta-analysis of six randomized, double-blind studies, some of which were published separately, ,,, with a total of 403 patients in which Ropivacaine 0.25% was compared with Bupivacaine 0.25%. They found that instrumental vaginal delivery was less frequent in women who received Ropivacaine compared with those who received Bupivacaine (27% vs. 40%; P < 0.01). In contrast, in our study, where we used smaller concentration of the study drugs, there was no significant difference in the mode of delivery in both the groups probably because the degree of motor block developed in Bupivacaine was not significant and did not affect the progress and mode of delivery, which is similar to the findings of various other studies. Although Campbell et al,  also found a comparatively less frequent incidence of forceps delivery and motor block in the Ropivacaine group, similar to Writer et al.'s results.
Parry et al, evaluated dorsal column somatosensory function, which is vibration and proprioception sense, and motor function of the lower limbs after epidural and spinal anesthesia, which is important for walking. They reported 90% patients who had received low-dose Bupivacaine/Fentanyl analgesia to have normal lower limb power and dorsal column function. But they also recommended complete evaluation of motor function and dorsal column function before allowing a patient to walk. Consistent with these studies, our patients were satisfied with their epidural in both the groups.
A finding of the 1990 survey on pain and childbirth showed that "feeling in control during labor is an important part of having a positive recollection of childbirth." 
Contrary to the popular belief that epidural analgesia causes prolongation of duration of labor, we found statistically significant reduction in the duration of labor in both the study groups, which was also observed by our obstetricians. We attribute this to the beneficial effects of analgesia that abolishes all sympathetic responses and makes uterine contractions more coordinated, apart from improving uterine blood flow. Similar findings were reported by Khan et al and Nafisi et al. , Reduction in duration of first stage of labor by 2 h was also observed by Lee et al., in the Ropivacaine group.  Adverse maternal events and fetal effects were statistically insignificant. Regarding the cost of Ropivacaine, it is twice that of Bupivacaine; but looking at the safety profile, we recommend using Ropivacaine.
The choice between intermittent dosing and continuous infusion depends on availability of equipments and rapidity with which the staff can respond to the patient request. We selected intermittent top-ups as our residents were enthusiastic, and we feel that experience is important in balancing between analgesia and maintaining mobility at the same time. Moreover, as per various other studies,  drug consumption is less in intermittent top-up doses, which certainly affects the development of motor block. Besides, close monitoring also develops confidence between the patient and the physician, and provides opportunity to recognize the complications immediately.
To conclude, we found that 0.125% Ropivacaine with Fentanyl 2 μg/ml produced excellent labor analgesia, which was clinically indistinguishable from a similar concentration of Bupivacaine and Fentanyl, with the advantage of less incidence of motor block and slightly longer duration of analgesia, apart from its lesser propensity to cause cardiotoxicity, when used as intermittent doses.
| References|| |
|1.||Reynolds F. Does the left hand know what the right hand is doing? An appraisal of single enantiomer local anaesthetics. Int J Obstet Anesth 1997;6:257-69. |
|2.||Lacassie HJ, Columb MO, Lacassie HP, Lantadilla RA. The relative motor blocking potencies of epidural Bupivacaine and Ropivacaine in labor. Anesth Analg 2002;95:204-8. |
|3.||Brockway MS, Bannister J, McClure JH, McKeown D, Wildsmith JA. Comparison of extradural Ropivacaine and Bupivacaine. Br J Anaesth 1991;66:31-7. |
|4.||Gautier P, De Kock M, Van Steenberge A, Miclot D, Fanard L, Hody JL. A double-blind comparison of 0.125% Ropivacaine with sufentanil and 0.125% Bupivacaine with sufentanil for epidural labor analgesia. Anesthesiology 1999;90:772-8. |
|5.||Lieberman E, Davidson K, Lee-Parritz A, Shearer E. Changes in fetal position during labor and their association with epidural analgesia. Obstet Gynecol 2005;105:974-82. |
|6.||Comparative Obstetric Mobile Epidural Trial (COMET) Study Group UK. Effect of low-dose mobile versus traditional epidural techniques on mode of delivery: A randomised controlled trial. Lancet 2001;358:19-23. |
|7.||Nageotte MP, Larson D, Rumney PJ, Sidhu M, Hollenbach K. Epidural analgesia compared with combined spinal-epidural analgesia during labor in nulliparous women. N Engl J Med 1997;337:1715-9. |
|8.||McCrae AF, Jozwiak H, McClure JH. Comparison of ropivacaine and bupivacaine in extradural analgesia for the relief of pain in labour. Br J Anaesth 1995;74:261-5. |
|9.||Muir HA, Writer D, Douglas J, Weeks S, Gambling D, Macarthur A. Double-blind comparison of epidural Ropivacaine 0.25% and Bupivacaine 0.25%, for the relief of childbirth pain. Can J Anaesth 1997;44:599-604. |
|10.||Writer WD, Stienstra R, Eddleston JM, Gatt SP, Griffin R, Gutsche BB, et al. Neonatal outcome and mode of delivery after epidural analgesia for labour with Ropivacaine and Bupivacaine: A prospective meta-analysis. Br J Anesth 1998;81:713-7. |
|11.||Nancarrow C, Rutten AJ, RuncimanWB, Mather LE, Carapetis RJ, McLean CF, et al. Myocardial and cerebral drug concentrations and the mechanisms of death after fatal intravenous doses of lidocaine, Bupivacaine and Ropivacaine in sheep. Anesth Analg 1989;69:276-83. |
|12.||Bader AM, Datta S, Flanagan H, Covino BG. Comparison of Bupivacaine and Ropivacaine induced conduction blockade in the isolated vagus nerve. Anesth Analg 1989;68:724-7. |
|13.||Owen MD, D'Angelo R, Gerancher JC, Thompson JM, Foss ML, Babb JD, et al. 125% Ropivacaine Is Similar to 0.125% Bupivacaine for Labor Analgesia Using Patient-Controlled Epidural Infusion. Anesth Analg 1998;86:527-31. |
|14.||Owen MD, Thomas JA, Smith T, Harris LC, D'Angelo R. Ropivacaine 0.075% and Bupivacaine 0.075% with Fentanyl 2g/mL are Equivalent for Labor Epidural Analgesia. Anesth Analg 2002;94:179-83. |
|15.||Meister GC, D'Angelo R, Owen M, Nelson KE, Gaver R. A Comparison of epidural analgesia with 0.125% Ropivacaine with Fentanyl Versus 0.125% Bupivacaine with Fentanyl during Labor. Anesth Analg 2000;90:632-7. |
|16.||Campbell DC, Zwack RM, Crone LA, Yip R. Ambulatory labor epidural analgesia: Bupivacaine versus Ropivacaine. Anesth Analg 2000;7:864-8. |
|17.||Beilin Y, Guinn NR, Bernstein HH, Zahn J, Hossain S, Bodian CA. Local anesthetics and mode of delivery: Bupivacaine versus ropivacaine versus levobupivacaine. Anesth Analg 2007;105:756-63. |
|18.||Segal BS, Birnbach DJ. Epidurals and cesarean deliveries: A new look at an old problem. Anesth Analg 2000;90:775-7. |
|19.||Stoddart AP, Nicholas KE, Popham PA. Low dose Bupivacaine/fentanyl epidural infusions in labour and mode of delivery. Anaesthesia 1994;49:1087-90. |
|20.||Goodfellow CF, Hull MG, Swaad DF, Dogterom J, Buijs RM. Oxytocin deficiency at delivery with epidural analgesia. Br J Obstet Gynaecol 1983;90:214-9. |
|21.||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. |
|22.||Polley LS, Columb MO, Naughton NN, Wagner DS, van de Ven CJ. Relative analgesic potencies of Ropivacaine and Bupivacaine for Epidural Analgesia in labour. Anesthesiology 1999;90:944-50. |
|23.||Eddleston JM, Holland JJ, Griffin RP, Corbett A, Horsman EL, Reynolds F. A double-blind comparison of 0.25% Ropivacaine and 0.25% Bupivacaine for extradural analgesia in labour. Br J Anaesth 1996;76:66-71. |
|24.||Gaiser RR, Venkateswaren P, Cheek TG, Persiley E, Buxbaum, J, Hedge J, et al. Comparision of 0.25% ropivacaine and Bupivacaine for epidural analgesia for labour and vaginal delivery. J Clin Anaesth 1997;9:564-8. |
|25.||Stienstra R, Jonker TA, Bourdrez P, Kuijpers JC, van Kleef JW, Lundberg U. Ropivacaine 0.25% versus bupivacaine 0.25% for continuous epidural analgesia in labor: A double-blind comparison. Anesth Analg 1995;80:285-9. |
|26.||Parry MG, Fernando R, Bawa GP, Poulton BB. Dorsal column function after epidural and spinal blockade- implications for the safety of walking following low-dose regional analgesia for labour. Anesthesia 1998;53:382-403. |
|27.||Collis RE, Plaat FS, Morgan BM. Comparison of midwife top-ups, continuous infusion and patient controlled epidural analgesia for maintaining mobility after a low dose combined spinal-epidural. Br J Anesth 1999;82:233-6. |
|28.||Nafisi S. Effects of epidural lidocaine analgesia on labor and delivery: A randomised, prospective, controlled trial. BMC Anesthesiol 2006;6:15. |
|29.||Khan MA, Yasin B, Zaffar M, ur Rehman S. Epidural analgesia; effect on the duration of labour. Prof Med J 2008;15:101-3. |
|30.||Lee BB, Ngan Kee WD, Ng FF, Lau TK, Wong EL. Epidural infusions of ropivacaine and bupivacaine for labor Analgesia: A randomized, double-blind study of obstetric outcome. Anesth Analg 2004;98:1145-52. |
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]