A Double-blind Comparison of 0.125% Ropivacaine with Sufentanil and 0.125% Bupivacaine with Sufentanil for Epidural Labor Analgesia 

The protocol was approved by the Clinical Research Practices Committee, and verbal informed consent was obtained from each patient. One hundred thirty-two American Society of Anesthesiologists physical status 1 or 2 parturients with singleton pregnancies in the vertex presentation were enrolled in the study. Uncomplicated course of pregnancy and normal fetal heart rate at the time of admission and randomization were mandatory inclusion criteria. All patients were para 0 or 1 and in active labor with cervical dilatation less than 5 cm when analgesia was requested. None received any analgesic agent before participation in the study.

Patients were placed in the lateral position, and an intravenous bolus dose of at least 250 ml lactated Ringer's solution was given. An 8-cm 16-gauge Tuohy needle (Portex, Portex Ltd., Hyde, Kent, UK) was inserted into the epidural space at the L2-L3 or L3-L4 interspaces by a loss-of-resistance technique, and a multiorifice epidural catheter was inserted 3 cm into the epidural space. Intravascular placement was ruled out by active aspiration of the catheter and by inspection of a dependent catheter for passive blood reflux. In the case of evident or questionable blood reflux, the catheter was removed and reinserted at a higher epidural space. No lidocaine/epinephrine test dose was used.

After the catheter was in place, in a first experiment, the 90 initial patients received, as determined by a Table ofrandom numbers, 10 ml of one of the following epidural solutions: bupivacaine 0.125% plus sufentanil 7.5 [micro sign]g (bupivacaine 0.125% group) or ropivacaine 0.125% plus sufentanil 7.5 [micro sign]g (ropivacaine 0.125% group). In a second experiment, 40 additional parturients were assigned randomly to receive one of the following blinded 10-ml solutions: bupivacaine 0.125% plus sufentanil 7.5 [micro sign]g (additional bupivacaine 0.125% group) or bupivacaine 0.100% plus sufentanil 7.5 [micro sign]g (additional bupivacaine 0.100% group). These additional patients were enrolled to evaluate the relative equipotency of two initial epidural solutions. This is particularly important for the interpretation of the data regarding motor blockade. The study solutions were prepared by an anesthesiologist not involved in the patients' care, and both the patient and the anesthesiologist who delivered analgesia were blinded to the study solutions.

Onset of analgesia was assessed using a pain relief score (0 = no relief; 1 = poor relief; 2 = important relief; 3 = complete relief) evaluated by the parturient during the first contractions after the epidural injection. A score of 2 or 3 was considered satisfactory. Pain was assessed with a 10-cm linear visual analogue scale (VAS) immediately before epidural placement and 5, 10, 15, 20, 30, 40, 60, 120, and 180 min after epidural injection. Additional VAS scores were obtained when epidural re-injection of tested solution was requested and after episiotomy, delivery, and suture. When the patient requested additional analgesia, 10 ml of the study solution was given through the epidural catheter by the anesthesiologist in charge. The duration of the analgesia provided by the epidural solutions was taken as the time elapsed between the initial or previous epidural injection and the first or subsequent additional analgesic request. No local anesthetic solutions other than the study solutions were given.

Motor blockade was assessed objectively by the investigators using a modified Bromage scale (1 = complete motor blockade; 2 = almost complete motor blockade-the patient is able only to move the feet; 3 = partial motor blockade-the patient is able to move the knees; 4 = detectable weakness of hip flexion-the patient is able to raise the leg but unable to keep it raised; 5 = no detectable weakness of hip flexion-the patient is able to keep the leg raised for 10 s or more; 6 = no weakness at all-the patient is able to perform partial knee bend while supine). [10]This test was performed before and 30 min after each epidural injection. Cephalad levels of anesthesia by sensory changes to pinprick were ascertained at the same moment. Thirty minutes after each epidural injection, patients subjectively rated nausea, sedation, and pruritus using the VAS. These parameters also were recorded after each 30-min period.

Blood pressure and heart rate were monitored using a noninvasive monitor (Cardiocap Datex, Helsinki, Finland) every 5 min (at least three times) before and 5, 10, 15, 20, 30, 45, 60, 90, 120, and 180 min after epidural injections. Baseline values for blood pressure and heart rate were the mean of the three measurements performed before epidural injection. Oxyhemoglobin saturation was monitored continuously by pulse oximetry in all patients. Fetal heart rate and uterine activity were monitored continuously throughout labor. The duration of labor, mode of delivery, and neonatal Apgar scores were recorded. All patients were seen the day after delivery at 9:00 AM and questioned about the quality of their analgesia using a four-point scale (0 = bad; 1 = moderate; 2 = good; 3 = excellent) considering the analgesia during labor and delivery and also the muscular strength. A score was obtained for each item.

Data are presented as mean +/− SD. The statistical analysis of onset, duration of analgesia, and pain (measured by VAS) was performed using two-sided unpaired Student's t tests at different times. The evaluation of motor blockade (six-point scale) and the parturient's evaluation of the quality of analgesia after the epidural injections were analyzed using Wilcoxon's rank sum test. Categoric variables were analyzed using the chi-square test or Fisher's exact test as appropriate. A P value <or= to 0.05 was considered statistically significant.

One hundred thirty-two patients were enrolled in the study. Two parturients did not complete the study protocol and were excluded from data analysis. Ninety patients were included in the first experiment and 40 were included in the second experiment. Treatment groups did not differ regarding demographic variables, VAS pain scores, parity, percentage undergoing induction, or cervical dilatation at the time of enrollment in the study. The duration of labor after epidural injections and the method of delivery were similar among the different groups (Table 1).

In both bupivacaine 0.125% groups and in the ropivacaine 0.125% group, onset of analgesia occurred after approximately 15 min and lasted +/− 90 min (Table 2). The onset of analgesia was significantly slower in the additional bupivacaine 0.100% group. Epidural bupivacaine 0.125% and ropivacaine 0.125% combined with sufentanil provided satisfactory analgesia as shown by the evolution of patient pain VAS scores (Figure 1).

A similar median level of sensory loss to pinprick in the midclavicular line was observed in all patients in the different study groups (T10). Patients' evaluations of their labor and delivery analgesia are summarized in Table 3.

After the third and the subsequent epidural injections, patients in the ropivacaine group experienced significantly less severe motor blockade than patients in the bupivacaine group (P < 0.05). However, patient pain VAS scores were comparable (Figure 2). At their postdelivery interview, patients in the ropivacaine group reported better muscular strength than patients in the bupivacaine 0.125% group (P < 0.05, Table 3).

Pruritus was present in 30% of the patients in the bupivacaine groups and in 31% of the patients in the ropivacaine group (not significant). Pain relief was associated with light sedation in approximately 35% of the patients. Moderate decreases in maternal baseline arterial blood pressure and heart rate were associated with pain relief in most patients. There were no differences, however, among the treatment groups. No patient required the administration of supplemental fluid loading or ephedrine. None of these episodes were associated with an abnormal fetal heart rate pattern.

None of the patients presented with nausea. The groups did not differ in mean respiratory rate, and in no parturient did respiratory rate decrease to < 12 breaths/min. Oxyhemoglobin saturation was > 95% in all patients at all times. Neonatal Apgar scores did not differ among groups. The subsequent course of the parturients was uneventful.

Our results show that low-dose epidurally administered ropivacaine (10 ml of 0.125%) associated with sufentanil (0.75 [micro sign]g/ml) produces adequate analgesia during labor. The onset and duration of this analgesia is comparable to the pain relief afforded by 10 ml bupivacaine, 0.125%, associated with sufentanil (0.75 [micro sign]g/ml). Furthermore, after repeated injections, fewer motor impairments were demonstrated in patients receiving the ropivacaine/sufentanil solution than in patients receiving the bupivacaine/sufentanil solution.

The observation that both epidural solutions produced comparable analgesia during labor is not surprising. Several clinical experiments showed that the new local anesthetic agent ropivacaine used alone provides reliable analgesia during labor. [11]Comparisons between ropivacaine 0.25 or 0.125% and bupivacaine 0.25 or 0.125% given as intermittent bolus doses or continuous infusion or using the patient-controlled epidural analgesia system failed to show any important differences regarding onset, duration, and quality of analgesia. [2,6-9]It is unlikely that adding an opioid to the ropivacaine solution would result in major differences compared with a bupivacaine- opioid solution. The addition of opioids to local anesthetic agents for analgesia during labor was popularized in the early 1980s. [12]This combination allows a significant reduction in the dose of local anesthetic agent and provides improved analgesia along with reduced incidence of instrumental deliveries. [13] 

More noteworthy is the significant difference in motor impairment conferred by ropivacaine and bupivacaine. Early clinical works with epidural ropivacaine suggest that this new local anesthetic agent may produce comparable analgesia with less motor blockade than does bupivacaine. [5,14]Currently, however, this issue is highly controversial. More than a specific drug-related effect, this reduction of motor impairment may be ascribed to the lower potency of ropivacaine compared with bupivacaine. Zaric et al. [15]showed that 0.25% bupivacaine produced more extensive sensory block than 0.3% ropivacaine, and most clinical studies suggest that ropivacaine is approximately 20% less potent than bupivacaine. [16]Are the results obtained in the current study able to discriminate between a specific drug effect or an effect directly related to the lower potency of ropivacaine? Our initial data were obtained using bupivacaine and ropivacaine at equal concentrations; consequently, the improved muscular strength noted may be ascribed simply to the lower overall degree of block from using a less potent drug. Nevertheless, results obtained in the additional groups comparing bupivacaine 0.125% plus sufentanil 7.5 [micro sign]g with bupivacaine 0.100% plus sufentanil 7.5 [micro sign]g argue for a specific drug effect. Despite a 20% reduction in the concentration of bupivacaine, similar levels of motor blockade were noted in these two additional groups. Meanwhile, the quality of the analgesia provided by bupivacaine 0.100% with sufentanil was poorer than with bupivacaine 0.125%. Concerning the bupivacaine-induced motor blockade, Russel [17]demonstrated nicely that this motor blockade is dependent on the cumulative dose of local anesthetic agent. In other words, motor blockade becomes progressively more severe with the duration of epidural analgesia. This phenomenon is clearly dramatic with plain bupivacaine administered at a rate of 10 ml/h. Nevertheless, it is still present in a group of patients having received a solution of bupivacaine 0.0625% with opioid. Twenty percent of these patients were unable to raise their leg after 4-6 h.

The reduced motor impairment observed after administration of ropivacaine seems to manifest only when very low doses of this local anesthetic agent are used. Zaric et al. [15]and Scott et al., [14]in two dose-effect studies comparing ropivacaine 0.1, 0.2, and 0.3%, one in volunteers and the second in postoperative patients, were unable to show any motor blockade with ropivacaine 0.1%. This dose, however, produced less efficient analgesia than the 0.2% solution. In contrast with these two studies and our results, Owen et al. [9]reported similar motor blockade when using patient-controlled epidural analgesia with ropivacaine 0.125% or bupivacaine 0.125% for analgesia during labor. [9]In this study, the mode of administration of local anesthetic agents may have influenced the motor impairment. These authors used a patient-controlled epidural analgesia mode with basal infusion that afforded an hourly use of local anesthetic agent of +/− 20 ml/h. It implies that the doses of local anesthetic agents delivered were higher than in our study and the other studies. They also administered 7 ml epidural 2% lidocaine before the start of the protocol. This test dose may have influenced the degree of motor blockade in both groups. Nevertheless, when investigating ropivacaine 0.125% plus 2 [micro sign]g/ml fentanyl compared with bupivacaine 0.125% plus 2 [micro sign]g/ml fentanyl, the same group of investigators reported equivalent analgesia with less motor block in the ropivacaine group. [18] 

Low concentrations of ropivacaine with sufentanil provide equivalent analgesia with less motor blockade than bupivacaine with sufentanil. This benefit, however, is not of major clinical importance because it becomes obvious only after the third epidural injection and has no influence on the rate of instrumental delivery.

The authors thank G. Byttebier, M.Sc., for helpful suggestions regarding statistical analysis and M. De Bosschere for technical assistance.