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A multicentre trial comparing different concentrations of ropivacaine plus sufentanil with bupivacaine plus sufentanil for patient-controlled epidural analgesia in labour

Gogarten, W.*; Van de Velde, M.; Soetens, F.; Van Aken, H.*; Brodner, G.*; Gramke, H.-F.*; Soetens, M.; Marcus, M. A. E.

European Journal of Anaesthesiology: January 2004 - Volume 21 - Issue 1 - p 38-45
Original Article
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Background and objective: To determine the optimal concentration of ropivacaine for bolus-only patient-controlled epidural labour analgesia, three different doses of ropivacaine were evaluated in comparison with bupivacaine in a double-blinded multicentre study.

Methods: Four hundred-and-fifty labouring parturients at term in three different academic institutions were randomized to four groups receiving bupivacaine 0.125% with sufentanil 0.75 μg mL−1, ropivacaine 0.125% or 0.175% with sufentanil 0.75 μg mL−1, or ropivacaine 0.2%. After an initial bolus of 10 mL of the study solution, and once visual analogue scores (VAS) were below 30 mm, patient-controlled epidural analgesia was initiated with a bolus of 4 mL, a lockout interval of 15 min and without a background infusion. Variables studied were the quality of analgesia, incidence of side-effects, the degree of motor blockade, and the mode of delivery.

Results: Bupivacaine 0.125% and ropivacaine 0.125% with sufentanil proved equally effective in providing labour analgesia without a difference in local anaesthetic consumption (48.6 ± 23 mg bupivacaine vs. 52.1 ± 38 mg ropivacaine), motor blockade or mode of delivery. Ropivacaine 0.175% plus sufentanil enhanced the quality of analgesia of the initial loading dose, whereas ropivacaine 0.2% without sufentanil increased the consumption of local anaesthetics (80.2 ± 34 mg; P < 0.05) and the degree of motor blockade.

Conclusion: Despite recent studies indicating that bupivacaine and ropivacaine may not be equipotent, both local anaesthetics provided equi-effective analgesia at equal doses without a difference in side-effects.

*Universitätsklinikum Münster, Department of Anaesthesiology and Intensive Care, Germany;Katholieke Universiteit Leuven, Department of Anesthesiology, Belgium;Sint Elisabeth Hospital, Department of Anesthesiology, Turnhout, Belgium;Academisch Ziekenhuis Maastricht, Department of Anaesthesiology and Pain Therapy, The Netherlands

Correspondence to: Hugo Van Aken, Department of Anaesthesiology and Intensive Care, Universitätsklinikum Münster, Albert-Schweitzer-Straße 33, D-48129 Münster, Germany. E-mail: hva@anit.uni-muenster.de; Tel: +49 251 8347251; Fax: +49 251 88704

Accepted for publication February 2003 EJA 1041

Ropivacaine is a new amide local anaesthetic with similar properties compared to bupivacaine. Potential advantages include a reduced cardiocirculatory and central nervous toxicity [1] and a higher selectivity for sensory fibres, producing a differential block with reduced motor impairment [2]. These advantages make ropivacaine, particularly, suitable for obstetric anaesthesia and several clinical trials with small patient numbers have been performed to determine its use for labour analgesia. Results of these previous trials were equivocal with most studies showing no differences in the quality of analgesia, incidence of motor blockade and mode of delivery [3-5]. Modes of application included continuous epidural infusions [3], intermittent bolus techniques [4] or patient-controlled epidural analgesia (PCEA) with background infusions [5]. PCEA techniques lead to increased patient satisfaction compared to intermittent top-up boluses [6], while decreasing overall local anaesthetic consumption and the number of interventions compared to continuous infusions [7]. The practice of adding a background infusion to PCEA for labour analgesia is controversial, as it increases drug consumption without any additional clinical benefit [8]. Optimal PCEA settings have not been determined. However, it has been recently suggested that a PCEA setting with a 12 mL bolus and a 25 min lockout interval provided superior analgesia and patient satisfaction compared to a PCEA with a bolus of 4 mL and a lockout interval of 8 min [9]. Moreover, the safety of PCEA techniques relies on small boluses, as patients may self-administer boluses in the absence of an anaesthesiologist once epidural analgesia has been started. The primary aim of this randomized double-blinded multicentre study was to determine a ropivacaine concentration combined with sufentanil 0.75 μg mL−1 that provides similar analgesia compared with the widely applied bupivacaine 0.125% with sufentanil, when used in a bolus-only PCEA mode, using small boluses and 15 min lockout intervals. Secondary aims were to evaluate whether ropivacaine possesses any advantages over bupivacaine in terms of side-effects, motor blockade and mode of delivery in this setting.

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Methods

Our Institutional Review Board approved this study and written informed consent was obtained from our patients. Four hundred-and-fifty term parturients (ASA I-II) carrying a single fetus in the vertex presentation were included in this prospective, double-blinded multicentre study. Patient consent was taken at the time of epidural request: this was considered appropriate as all drugs used in the present study are approved for clinical use and analgesia was not with-held from any patient. Patients were randomly assigned to four groups by drawing consecutive sealed envelopes, which also included the vials containing the study drugs. Two Belgian and one German hospital participated in this study. Patients, anaesthesiologists, obstetricians and neonatologists were unaware of the local anaesthetic mixture, which had been prepared by the local pharmacy. A power analysis determined the necessary group size to detect a 20% difference in the amount of local anaesthetics used as 110 patients per group (β = 0.8, α = 0.05). An additional 10 parturients were randomized to allow for protocol violations and loss of data.

Study patients were in spontaneous labour at term (>36 weeks of gestation), and had requested epidural analgesia. Exclusion criteria included prior administration of sedatives, analgesics, confounding medical disease, premature labour and contraindications for regional anaesthesia.

The epidural puncture was performed at either the L2-L3 or L3-L4 interspace with the women in the left-lateral position. The epidural space was identified by loss of resistance to physiological saline using either an 18-G or a 16-G Tuohy needle, and a Portex® (Portex Ltd, Hythe, Kent, UK) multi-orifice catheter was inserted into the epidural space. Intravascular catheter misplacement was tested by frequent catheter aspiration without administration of an epinephrine-containing test dose. All patients received 500 mL of lactated Ringer's solution intravenously.

Epidural analgesia was induced with bupivacaine 10 mL 0.125% with sufentanil 0.75 μg mL−1 (G1), ropivacaine 0.125% with sufentanil 0.75 μg mL−1 (G2), ropivacaine 0.175% with sufentanil 0.75 μg mL−1 (G3) or ropivacaine 0.2% without sufentanil (G4) in a double-blinded fashion. The concentration of sufentanil was based on a previous report demonstrating optimal labour analgesia in combination with bupivacaine 10 mL 0.125% [10]. This dose was given in 5 mL increments separated by at least 5 min and served as the test dose. During the injection of the loading dose(s) and for the following 10 min, parturients were placed in the supine position with a left-lateral tilt. Contraction pain was evaluated immediately after the last contraction with a visual analogue score scale (VAS; 0: no pain; 100 mm: worst imaginable pain) before the first epidural injection, and after 10, 20, 30 and 40 min. Subsequently, VAS scores were evaluated hourly, at the end of the first stage of labour, after delivery and retrospectively for the episiotomy. If VAS scores remained >30 mm, 20 min after the first injection, a second dose of 10 mL of the study solution was given. If VAS scores persisted above 30 mm after two boluses, the catheter was deemed malpositioned and patients were excluded from the study. PCEA was started once VAS scores were below 30 mm with a bolus of 4 mL of the study solution, a lockout interval of 15 min and no background infusion. If the maximum dose of sufentanil (30 μg) had been given, the sufentanil was omitted and analgesia was provided with plain local anaesthetic study solutions. Plain local anaesthetic solutions were also provided by the pharmacy together with the vials containing sufentanil, and were marked as plain local anaesthetics. The total amount of sufentanil was limited to 30 μg, as this dose had been demonstrated to be safe for the newborn in previous studies [11,12].

The level of sensory dermatomal spread was determined by pinprick. The degree of motor blockade was assessed using a modified Bromage score at hourly intervals (full range of motion = 0; moves feet and knees = 1; moves feet only = 2; unable to move feet or knees = 3). The function of the rectus abdominis muscle (RAM-test) [13] was evaluated before the first epidural injection and at the end of the first stage of labour to test the influence of epidural analgesia on the ability to push. A score of 100% implies that the patient manages to sit up from the supine position with her arms folded behind her head. A score of 80% equals elevation from the supine position with arms stretched in front, 60% equals elevation of the scapulae, 40% elevation of the shoulders only and 20% increased tension of the abdominal muscles without visible movement of the torso.

Fetal and maternal heart rates were continuously monitored during epidural injections. Maternal blood pressure was monitored non-invasively. Hypotension was defined as a decrease in systolic arterial pressure below 100 mmHg or a decrease of 30% from baseline and was treated with small boluses of etilefrine or ephedrine, depending on the standard protocol of the participating centre.

In addition to motor blockade and hypotension, the following side-effects were assessed throughout labour and delivery: pruritus, nausea, vomiting and shivering.

Duration of labour, mode of delivery, neonatal Apgar scores and hourly local anaesthetic consumption were recorded in all patients. The method of delivery was left to the discretion of the attending obstetrician.

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Statistical analysis

All values were given as mean ± standard deviation where appropriate. VAS scores are given as median plus range. Statistical analysis was performed using the SPSS® program (SPSS Inc, Chicago, ILL, USA). It included analysis of variance, χ-2 test or Scheffé test. P ≤ 0.05 was considered significant. Nonparametric data were analysed with the Kruskal-Wallis test.

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Results

Of the 450 patients enrolled in the study, 39 had to be excluded due to insufficient analgesia after two boluses of the study solution. A second bolus of 10 mL, 20 min after the first injection, was necessary in 13 patients of G1, 15 patients of G2, 11 patients of G3, and 35 patients of G4. This was significant for G4 (P < 0.05 vs. G1-3). Forty minutes after the first injection, no patient of G3 had a VAS score greater than 30 mm (P < 0.05). In 11 patients of G1, 11 patients of G2, and 17 patients of G4 VAS scores were still above 30 mm after 40 min and the second bolus. These patients were excluded from further analysis (Fig. 1). Reasons were either suspected catheter malposition or advanced labour, necessitating higher doses of local anaesthetics. There were no patient characteristics differences between the study groups and treatment groups did not differ regarding parity or cervical dilation at the start of epidural analgesia (Table 1).

Figure 1

Figure 1

Table 1

Table 1

The quality of analgesia and the level of sensory dermatomal spread were comparable among the different groups throughout the study period. VAS scores in G4 (ropivacaine 0.2% without sufentanil) were slightly higher, but this difference did not reach significance (Table 2). PCEA demands were significantly higher in G4 (P < 0.05), but due to lockout intervals, the number of delivered PCEA boluses did not differ (Fig. 2).

Table 2

Table 2

Figure 2

Figure 2

The mean total amount of epidurally administered medication was 38.9 ± 18 mL (48.6 ± 23 mg bupivacaine) in G1, 41.7 ± 30 mL (52.1 ± 38 mg ropivacaine) in G2, 34.7 ± 19 mL (60.7 ± 33 mg ropivacaine) in G3 and 40.1 ± 17 mL (80.2 ± 34 mg ropivacaine) in G4. Due to the higher local anaesthetic concentration the amount of local anaesthetics used in G4 was significantly increased compared to G1-G3 (P < 0.05). The incidence of side-effects was similar in all four groups except for pruritus, which was significantly less frequent in the group treated with ropivacaine 0.2% without sufentanil (Table 3).

Table 3

Table 3

Patients included in the analysis of motor function are depicted in Figure 3. Modified Bromage scores were comparable for G1, G2 and G3. G4 had a significantly higher incidence of motor blockade after 2 h (Table 4), although the average score in this group did not exceed 1. Strength of the abdominal muscles, as assessed by the RAM-test, did not decrease after initiation of epidural analgesia and did not differ between groups (Table 5).

Figure 3

Figure 3

Table 4

Table 4

Table 5

Table 5

There were no differences in the duration of the first or second stage of labour. Moreover, the incidence of instrumental deliveries and Caesarean sections was identical in all groups (Table 6).

Table 6

Table 6

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Discussion

The results of the present multicentre trial demonstrate a comparable analgesic efficacy of ropivacaine 0.125% and bupivacaine 0.125% combined with sufentanil, while ropivacaine 0.175% proved slightly superior in the initiation of labour analgesia without enhancing motor blockade. The two local anaesthetics, thus, appeared clinically indistinguishable.

Ropivacaine has been shown to produce less toxicity and motor blockade compared to bupivacaine in equal concentrations [1,2], indicating a superior safety profile when used for regional anaesthesia. These advantages of ropivacaine have been challenged by Capogna and colleagues [14] and Polley and colleagues [15], who demonstrated a difference in analgesic potency between ropivacaine and bupivacaine with a potency ratio of 0.6 using the up-down sequential allocation method. These authors also suggested that previous studies comparing both local anaesthetics applied concentrations that were too high and well beyond the steep part of the dose-response curve to detect significant differences. In support of the different potencies Fernández-Guisasola and colleagues [16] reported a similar analgesic effect of continuous infusions of bupivacaine 0.0625% and ropivacaine 0.1% in the presence of fentanyl.

Although the determination of minimal local anaesthetic concentration (MLAC) has undoubtedly added valuable information to our current understanding of local anaesthetics, there are several caveats when applying these results to the clinical situation throughout labour. First, they only evaluate the concentration necessary for the initiation of labour analgesia as opposed to doses necessary throughout labour and delivery. Second, reported effective concentrations to obtain analgesia in 50% of patients (EC50) merely represent one point of the dose-response curve. They do not predict whether the slopes of the dose-response curves of the two drugs are identical or whether they overlap at higher and clinically more relevant concentrations (e.g. the EC95). Third, the EC50 is determined with a VAS score below 10 mm defined as successful analgesia. Clinically, VAS scores below 20-30 mm are considered sufficient and are in the range that parturients choose, when using a PCEA device. The EC50 determined in MLAC studies may, therefore, not be identical to the EC50 to obtain a VAS score <30 mm. Fourth, the up-down sequential allocation method focuses on the concentration of the local anaesthetic given in a large dilute volume. This focus on concentration rather than on dose may have distorted the interpretation of previous studies and has led to new studies comparing lower concentrations closer to the EC50[17]. However, several studies have shown that the intensity of sensory and motor blockade is dependent on total local anaesthetic dose rather than concentration [18-20], and studies should not be refuted based on concentration alone.

In the present study, local anaesthetic concentrations were high and well above the respective EC50, but total doses throughout labour and delivery were low. On a milligram basis, the initial dose of ropivacaine 10 mL 0.175% (17.5 mg) plus sufentanil (7.5 μg) in the present study did not contain more ropivacaine than the EC50 of ropivacaine in the presence of sufentanil (ropivacaine 20 mL 0.09%; or 18 mg) [21], although Palm and colleagues used twice the dose of sufentanil (15 μg). However, this dose provided satisfactory analgesia in 89% of patients in the present study, and underscores the fact that the EC50 required to obtain a VAS score <10 mm is different from that to obtain a VAS score <30 mm. Similarly, our concentration of bupivacaine and sufentanil appear to be high, since Polley and colleagues [22] determined the EC50 of bupivacaine in the presence of sufentanil 0.5 μg mL−1 to be 0.048%, but again - in terms of total milligrams of bupivacaine and sufentanil applied - these doses are rather similar (e.g. bupivacaine 9.6 mg plus sufentanil 10 μg vs. bupivacaine 12.5 mg plus sufentanil 7.5 μg in the present study). Again, the low doses of bupivacaine and sufentanil applied in the present study provided satisfactory analgesia in 87% of patients. The dose of sufentanil added to local anaesthetics has been previously demonstrated to be the optimal dose [23] and is below the doses of sufentanil reported by Polley and colleagues [22]. Although the addition of sufentanil may have masked differences between the two local anaesthetics in terms of potency, sufentanil would have prolonged the duration of the epidural solution in an identical fashion in all opioid groups, and thus, does not confound the present results. Moreover, the addition of potent opioids represents current standard and the results are, therefore, applicable to clinical practice. The low doses of opioids used would not suffice to provide efficient analgesia without the concurrent addition of local anaesthetics.

The interpretation of previous results may additionally be confounded by the mode of application of the local anaesthetic solution. Finegold and colleagues [24] recently demonstrated a similar analgesic efficacy of ropivacaine 0.1% compared to bupivacaine 0.125%, using continuous infusions. However, continuous infusions increase total overall local anaesthetic doses and may have masked any true differences between the two drugs.

If local anaesthetics are delivered on demand only via intermittent top-up boluses or a PCEA device, differences in potencies should lead to higher local anaesthetic requirements in patients treated with ropivacaine. Gautier and colleagues [4] used intermittent top-up boluses and showed similar analgesic efficacy of ropivacaine 0.125% and bupivacaine 0.125%, whereas bupivacaine 0.1% increased the number of boluses needed to provide effective analgesia, indicating that both drugs are equally effective when used in identical concentrations. Similarly, we did not observe any differences in PCEA requirements between the two drugs.

Fischer and colleagues [25] and Meister and colleagues [26] used a PCEA technique and demonstrated a similar analgesic effect of ropivacaine and bupivacaine in equal concentrations without differences in local anaesthetic consumption. In the latter study, ropivacaine produced less motor blockade than bupivacaine, which may have resulted from the addition of a background infusion. Total doses applied were much higher than in the present study using a bolus-only mode, and may have only been below the threshold for producing motor blockade with ropivacaine but not with bupivacaine. In a subsequent study, the same group was unable to demonstrate any differences in analgesic quality or motor blockade between ropivacaine 0.075% and bupivacaine 0.075% [17], although total doses of local anaesthetics were still higher than in the present study. We included the RAM-test to enhance the sensitivity of testing motor strength, which may be more relevant to test the expulsive forces generated in the second stage of labour. We were, nevertheless, unable to detect any significant differences in motor blockade.

Our study, thus, confirms that ropivacaine and bupivacaine are clinically equivalent in providing labour analgesia and suggests that the slope and shape of the dose-response curves of the two drugs may be closer together at the high end of the dose-response curve than derived from the up-down sequential allocation method. A 40% difference in potency of the EC50 may, therefore, not be extrapolated to a 40% difference of the EC95, until confirmed by traditional dose-response curves. The validity of applying an EC50 obtained from up-down sequential allocation to clinical endpoints has previously been questioned [27,28], and doses of ropivacaine for labour analgesia should not be increased based on these results alone. Our results also indicate that advantages of ropivacaine in terms of motor blockade are only apparent, if high doses of local anaesthetics independent of the concentration are used.

Advantages of ropivacaine in respect to toxicity are irrelevant in labour analgesia but may be of clinical importance for Caesarean section, provided that similar doses of both local anaesthetics can be administered. Datta and colleagues [29] demonstrated that equal doses of both local anaesthetics provide satisfactory anaesthesia with a comparable onset time, duration and spread of anaesthesia, but with a significantly shorter motor blockade after ropivacaine.

We did not observe any differences in instrumental deliveries and Caesarean sections. Although indications for instrumental deliveries and Caesarean sections were left to the discretion of the attending obstetrician, bias should be negligible with a study population of 411 patients, equally distributed among the different hospitals. In addition, Vertommen and colleagues [12] reported a similar incidence of Caesarean sections under epidural analgesia for two of the participating centres in 1991.

In summary, our data indicate that bupivacaine 0.125% and ropivacaine 0.125% in combination with sufentanil are equally effective in providing satisfactory labour analgesia. If analgesia is delivered with patient-controlled devices and without a background infusion, overall drug consumption appears to be below the threshold of inducing a significant motor blockade with both local anaesthetic drugs.

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Acknowledgements

Funding: Department of Anaesthesiology and Intensive Care, Universitätsklinikum Münster, Germany. This study was presented in part at the 1999 Annual Meeting of the ASA, Dallas, Texas, USA.

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Keywords:

ANAESTHETICS, LOCAL; ropivacaine, bupivacaine; ANALGESIA, EPIDURAL; ANALGESIA, PATIENT-CONTROLLED; NARCOTICS, sufentanil; OBSTETRICS; PREGNANCY

© 2004 European Academy of Anaesthesiology