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OBSTETRIC ANESTHESIA

A Comparison of Epidural Analgesia with 0.125% Ropivacaine with Fentanyl Versus 0.125% Bupivacaine with Fentanyl during Labor

Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina

Address correspondence and reprint requests to Robert D’Angelo, MD, Obstetric Anesthesia, Forsyth Medical Center, 3333 Silas Creek Pkwy., Winston-Salem, NC 27103. Address e-mail to rdangelo{at}wfubmc.edu

	Abstract

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We previously found that the extent of an epidural motor block produced by 0.125% ropivacaine was clinically indistinguishable from 0.125% bupivacaine in laboring patients. By adding fentanyl to the 0.125% ropivacaine and bupivacaine solutions in an attempt to reduce hourly local anesthetic requirements, we hypothesized that differences in motor block produced by the two drugs may become apparent. Fifty laboring women were randomized to receive either 0.125% ropivacaine with fentanyl 2 µg/mL or an equivalent concentration of bupivacaine/fentanyl using patient-controlled epidural analgesia (PCEA) with settings of: 6-mL/hr basal rate, 5-mL bolus, 10-min lockout, 30-mL/h dose limit. Analgesia, local anesthetic use, motor block, patient satisfaction, and side effects were assessed until the time of delivery. No differences in verbal pain scores, local anesthetic use, patient satisfaction, or side effects between groups were observed; however, patients administered ropivacaine/fentanyl developed significantly less motor block than patients administered bupivacaine/fentanyl. Ropivacaine 0.125% with fentanyl 2 µg/mL produces similar labor analgesia with significantly less motor block than an equivalent concentration of bupivacaine/fentanyl. Whether this statistical reduction in motor block improves clinical outcome or is applicable to anesthesia practices which do not use the PCEA technique remains to be determined.

Implications: By using a patient-controlled epidural analgesia technique, ropivacaine 0.125% with fentanyl 2 µg/mL produces similar analgesia with significantly less motor block than a similar concentration of bupivacaine with fentanyl during labor. Whether this statistical reduction in motor block improves clinical outcome or is applicable to anesthesia practices which do not use the patient-controlled epidural analgesia technique remains to be determined.

	Introduction

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Ropivacaine is an amide local anesthetic released for clinical use in 1996. Preclinical animal (1–2) and human studies (3–4) suggest that ropivacaine produces less motor block than bupivacaine. In contrast, clinical labor studies comparing ropivacaine with bupivacaine in 0.2%–0.25% concentrations demonstrate no differences in motor block between these drugs (5–10). Likewise, we recently compared 0.125% ropivacaine with 0.125% bupivacaine in laboring patients using a patient-controlled epidural analgesia (PCEA) technique and reported no differences in analgesia, total drug use, patient satisfaction, or the degree of motor block between groups (11). Mean hourly drug use was approximately 19 mL/hr for each group. It is possible that differences in motor block become less apparent between drugs at this hourly dose. Because fentanyl reduces local anesthetic requirements by approximately 25% (12–14), fentanyl was added to the 0.125% ropivacaine and bupivacaine solutions in our study. We hypothesized that reducing hourly local anesthetic use may allow differences in motor block produced by ropivacaine and bupivacaine to be more readily detected.

	Methods

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After institutional review board approval and written, informed consent, 70 ASA physical status I or II parturients in active labor with a cervical dilation of 3–6 cm requesting epidural analgesia were randomized by using a computer-generated table of random numbers. By double-blinded design, patients received epidural infusions of either 0.125% ropivacaine with fentanyl 2 µg/mL or 0.125% bupivacaine with fentanyl 2 µg/mL. Study solutions were prepared by an anesthesiologist not directly involved in the patient’s care or data collection. Exclusion criteria included multiple or preterm gestation pregnancies, weight > 250 lbs, age < 18 yr, administration of IV analgesics within 1 h of epidural request, allergy to any study drug, or contraindication to epidural analgesia.

Automated maternal blood pressure and heart rate, tocodynamometry, and continuous fetal heart rate were monitored throughout labor. After insertion of a multiorifice epidural catheter (B. Braun Medical, Bethlehem, PA) 4 cm into the epidural space at the L2-3 or L3-4 interspace, a combined subarachnoid and IV test dose of 3 mL of 1.5% lidocaine with epinephrine 15 µg was administered. Patients who did not experience symptoms from the test dose received 15 mL epidural injections of either 0.125% ropivacaine with fentanyl 2 µg/mL or 0.125% bupivacaine with fentanyl 2 µg/mL in 5 mL increments over 10 min. Patients not experiencing analgesia within 15 min of study drug administration were excluded. Analgesia was maintained throughout labor by PCEA (Graseby 3300 PCA pump; Graseby Medical LTD, Watford, UK) with the following variables: 6-mL/hr basal infusion, 5-mL patient-controlled bolus, 10-min lockout, 30-mL/h limit. Patients who experienced inadequate analgesia during labor, defined as a patient requesting additional analgesia irrespective of PCEA use, received an additional 10-mL bolus of study solution in 5-mL increments through the PCEA device. Patients with persistent inadequate analgesia requiring manipulation of the epidural catheter or who delivered within 2 h of epidural catheter placement were excluded from data analysis. Hypotension, defined as symptomatic systolic blood pressure < 100 mm Hg or a >20% reduction from baseline, was treated with additional left uterine displacement, maternal oxygen administration, IV fluid bolus, or ephedrine as indicated. Pain intensity by using a numeric rating scale (NRS; 0 = no pain, 10 = worst pain imaginable), sensory levels to pinprick, motor block by using a 0–3 scale (0 = can raise extended leg off bed, 1 = able to bend knees, 2 = able to move only ankles, 3 = unable to bend knees or ankles), and side effects including nausea, pruritus, and respiratory depression were assessed at baseline, 5 min, 60 min, then every 2 h until complete cervical dilation, and at delivery. Patients were asked to rate pain intensity during uterine contractions.

Cumulative study solution volumes, PCEA demands, and delivered demand doses were recorded at complete cervical dilation and at delivery. Patients requiring supplemental perineal analgesia for vaginal delivery received 10–15 mL of either 2% or 3% 2-chloroprocaine as indicated. Patient satisfaction was assessed immediately after delivery as excellent, good, fair, or poor.

Statistical analyses were performed by using Sigmastat (SPSS Inc., Chicago, IL) or SAS (Statistical Analysis System, Inc., Cary, NC). Unless otherwise indicated, data were presented as mean ± SD. Statistical analyses included analysis of variance, ² (2), and Fisher’s exact tests as appropriate. P < 0.05 was considered significant. Group size (25 patients per group) was selected by using proportions sample size estimates (power = 80%, á = 0.05) to detect a 40% difference in the occurrence of motor block between groups. The incidence of significant motor block (2 or 3 on a 0–3 scale) was assumed to be 30% (11).

	Results

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Seventy patients were enrolled, and 50 completed the study. Of patients completing the study, 25 received ropivacaine/fentanyl, and 25 received bupivacaine/fentanyl. Twenty patients were excluded for the following reasons: delivery within 2 h of epidural placement (7 in the ropivacaine group, 5 in the bupivacaine group), inadequate analgesia requiring catheter manipulation (2 in the ropivacaine group, 1 in the bupivacaine group), and protocol deviation (4 in the ropivacaine group, 1 in the bupivacaine group).

Demographic variables were similar between groups (Table 1). Likewise, parity, duration of analgesia, oxytocin use, mode of delivery, sensory levels to pinprick, NRS scores before or after epidural catheter placement, and patient satisfaction were similar between groups (Table 1).

View larger version (17K): [in this window] [in a new window]   Figure 1. The figure indicates percentage of patients developing motor block during labor. The most intense motor block experienced by each patient at any assessment interval throughout labor is presented. Patient-controlled infusions of either 0.125% ropivacaine with fentanyl 2 µg/mL or 0.125% bupivacaine with fentanyl 2 µg/mL were administered. Motor block was assessed on a 0–3 scale: 0 = can raise leg off bed, 1 = able only to bend knees, 2 = able only to move ankles, 3 = no leg movement. The asterisk (*) represents a significant difference between groups, P < 0.05 considered significant. Patients administered ropivacaine/fentanyl developed significantly less motor block than patients administered bupivacaine/fentanyl.

	Discussion

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In this study, 0.125% ropivacaine with fentanyl 2 µg/mL produced equivalent analgesia with significantly less motor block than 0.125% bupivacaine with fentanyl 2 µg/mL. These results are in contrast to our previous study in which 0.125% ropivacaine and 0.125% bupivacaine produced equivalent analgesia and motor block (11). We attribute the differences in motor block between the two studies to modifications in study design. The addition of fentanyl to the epidural solutions reduced hourly local anesthetic use from approximately 19 mL/h in the previous study to 13.7 mL/h in the current study. This 28% reduction in mean hourly local anesthetic use between studies supports evidence that epidural fentanyl reduces local anesthetic requirements by 19%–31% (12–14). There is a threshold for producing motor block that is exceeded at higher local anesthetic doses. The dose of ropivacaine required in the current study, but not that of bupivacaine, may have decreased below this threshold, thus allowing us to detect subtle differences in motor block between these drugs.

Another factor in our previous study, which may have affected motor block, was the initial epidural test dose. In the previous study, each epidural catheter was tested for location with 7 mL of 2% lidocaine (2 mL spinal and 5 mL IV tests). Patients were enrolled in the study only if adequate analgesia was produced by the lidocaine test doses. We were concerned that patients with inadequate analgesia caused by incorrect epidural catheter placement might self-administer excessive amounts of local anesthetic with the PCEA technique. We assumed any motor block produced by the lidocaine test doses would dissipate within approximately one hour, thereby still allowing us to detect differences in motor block between drugs when patients required epidural analgesia for more than two hours. However, the motor block produced by the lidocaine may have had long-lasting, subtle effects that masked differences in motor block between ropivacaine and bupivacaine. To reduce motor block produced by the lidocaine test dose in our current study, epidural catheters were tested with a single 3-mL bolus of 1.5% lidocaine with epinephrine 15 µg. As a result, patients developed significantly less initial motor block from the lidocaine test dose in the current study (2% vs 69% in the first study). It is unclear if the differences in motor block detected between the two studies are primarily related to altering the lidocaine test dose or from reducing the hourly local anesthetic use after the addition of fentanyl. It is likely that both variables contributed to the contrasting findings.

Patients administered bupivacaine/fentanyl may have developed significantly more motor block than patients administered ropivacaine/fentanyl because they also required significantly more supplemental analgesia during labor. Although possible, this is unlikely, because the mean hourly local anesthetic requirements were similar between groups (Table 2), and all supplemental boluses were of study solution, not of a more concentrated solution which may be more likely to produce motor block. Additionally, although patients administered ropivacaine/fentanyl more often had no motor block compared to patients administered bupivacaine/fentanyl, the degree of motor block produced by either solution was minimal. All patients administered ropivacaine/fentanyl, and 96% administered bupivacaine/fentanyl had motor block scores of either 0 or 1 (0–3 scale). Only one patient administered bupivacaine/fentanyl developed moderate motor block (2 on a 0–3 scale) with no patient in either group developing profound motor block (3 on a 0–3 scale). Whether this statistical reduction in mild motor block from 0.125% ropivacaine with fentanyl improves clinical outcome remains unknown. In the current study, ropivacaine/fentanyl did not shorten the duration of labor or affect the mode of delivery (Table 1); however, the 50 patients enrolled were insufficient to adequately test for outcome variables. In addition, it is important to note that our results may not be applicable to obstetric anesthesia practices that administer more concentrated local anesthetic solutions or which use continuous infusion or intermittent bolus techniques rather than a PCEA technique to provide labor analgesia.

Although significantly more patients in the bupivacaine/fentanyl group required supplemental analgesia during labor, more patients in the ropivacaine/fentanyl group required supplemental local anesthetic at the time of delivery, although the difference did not reach statistical significance (Table 2). Patients in the bupivacaine/fentanyl group may have required less supplementation for delivery simply because they had received additional supplementation during labor. In total, 56% of the patients administered ropivacaine/fentanyl versus 68% administered bupivacaine/fentanyl received supplemental analgesia during either labor or for delivery, suggesting little overall difference between groups. Likewise, the similarity in NRS pain scores throughout labor and immediately after delivery, as well as overall patient satisfaction between groups, also suggests both solutions produce overall equivalent analgesia.

We did not examine the mechanism by which ropivacaine and bupivacaine produce motor block. However, we speculate the differences in motor block observed in this study may be related to the physiochemical properties of the two drugs. Ropivacaine is prepared as an almost pure (>99%) L-isomer, whereas bupivacaine is prepared as a racemic (50–50) mixture of the D- and L-isomers. Other than these racemic differences, ropivacaine contains a 3-carbon side chain, whereas bupivacaine contains a 4-carbon side chain. It is possible the D-isomer or the extra carbon in the side chain of bupivacaine somehow alters receptor binding so that more motor block is produced. Another distinct possibility may be related to differences in potency between drugs. Three recent studies suggest ropivacaine is 40%–50% less potent than bupivacaine (15–17). If true, because similar concentrations of ropivacaine and bupivacaine were used in the current study, relatively more bupivacaine was administered. Thus, differences in motor block between drugs may simply reflect the higher relative dose of bupivacaine rather than inherent differences in physiochemical properties between drugs.

Further discussion of the relative potencies of ropivacaine and bupivacaine is warranted. Although three recent studies suggest ropivacaine is less potent than bupivacaine (15–17), the two drugs appear to be equipotent at clinically used concentrations. Polley et al. (15) and Capogna et al. (16) estimated the minimum local analgesic concentrations of ropivacaine and bupivacaine using an up-down sequential allocation study design. By definition, they estimated a dose of local anesthetic that produces labor analgesia in only 50% of the patients. In contrast, McDonald et al. (17) compared spinal ropivacaine with spinal bupivacaine in volunteers not in labor or undergoing surgery. The applicability of the findings of these three studies to clinical practice remains unknown. In contrast, we administered local anesthetics to produce clinical analgesia in labor patients, and our findings suggest 0.125% ropivacaine and 0.125% bupivacaine are equipotent as demonstrated by mean hourly drug use, NRS scores to pain, sensory levels to pinprick, and overall patient satisfaction. Differences in potency between bupivacaine and ropivacaine would have been obscured in our studies had we used a continuous infusion technique in which the hourly administration rate exceeded the mean hourly local anesthetic requirement (13.7 mL/h). In contrast, a PCEA technique with the basal rate set much lower than the minimal hourly requirement (6 vs 13 mL/h) avoided this confounding variable. If ropivacaine is significantly less potent than bupivacaine, patients should have self-administered proportionally more ropivacaine than bupivacaine, which was not the case in either of our studies. Furthermore, patients administered bupivacaine/fentanyl required significantly more supplemental analgesia during labor than patients administered ropivacaine/fentanyl in the current study. The opposite would be predicted if ropivacaine were significantly less potent than bupivacaine. Additional studies examining the relative potencies of ropivacaine and bupivacaine in the clinical setting are warranted.

In summary, using a PCEA technique, 0.125% ropivacaine with fentanyl 2 µg/mL produces excellent labor analgesia clinically indistinguishable from a similar concentration of bupivacaine/fentanyl, except that patients developed significantly less motor block with ropivacaine/fentanyl. Whether this statistical reduction in motor block improves clinical outcome or is applicable to anesthesia practices not using the PCEA technique remains to be determined.

	References

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This Article Abstract Full Text (PDF) En Espanol Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (46) Citing Articles via Google Scholar Google Scholar Articles by Meister, G. C. Articles by Gaver, R. Search for Related Content PubMed PubMed Citation Articles by Meister, G. C. Articles by Gaver, R.

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999