A Comparison of 0.5% Bupivacaine, 0.5% Ropivacaine, and 0.75% Ropivacaine for Interscalene Brachial Plexus Block

Abstract

The onset time and duration of action of ropivacaine during an interscalene block are not known.The potentially improved safety profile of ropivacaine may allow the use of higher concentrations to try and speed onset time. We compared bupivacaine and ropivacaine to determine the optimal long-acting local anesthetic and concentration for interscalene brachial plexus block. Seventy-five adult patients scheduled for outpatient shoulder surgery under interscalene block were entered into this double-blind, randomized study. Patients were assigned (n = 25 per group) to receive an interscalene block using 30 mL of 0.5% bupivacaine, 0.5% ropivacaine, or 0.75% ropivacaine. All solutions contained fresh epinephrine in a 1:400,000 concentration. At 1-min intervals after local anesthetic injection, patients were assessed to determine loss of shoulder abduction and loss of pinprick in the C5-6 dermatomes. Before discharge, patients were asked to document the time of first oral narcotic use, when incisional discomfort began, and when full sensation returned to the shoulder. The mean onset time of both motor and sensory blockade was <6 min in all groups. Duration of sensory blockade was similar in all groups as defined by the three recovery measures. We conclude that there is no clinically important difference in times to onset and recovery of interscalene block for bupivacaine 0.5%, ropivacaine 0.5%, and ropivacaine 0.75% when injected in equal volumes. Implications: In this study, we demonstrated a similar efficacy between equal concentrations of ropivacaine and bupivacaine. In addition, increasing the concentration of ropivacaine from 0.5% to 0.75% fails to improve the onset or duration of interscalene brachial plexus block.

(Anesth Analg 1998;87:1316-9)

Section Editor: Denise J. Wedel.

Ropivacaine is a long-acting amide local anesthetic with a potentially improved safety profile when contrasted to bupivacaine ^[1,2]. Human trials have demonstrated less cardiac depression and fewer central nervous system effects when ropivacaine is injected IV. The fact that ropivacaine may offer less cardiac and neurologic toxicity with intravascular injection suggests a potential clinical advantage of this drug during neural blockade when large volumes of local anesthetic are required. This property may also enable the use of solutions with a higher concentration to enhance the speed of onset time and to prolong duration. However, if onset time and duration of neural blockade are not adequate, substitution for bupivacaine may not be appropriate. Currently, information about the onset time and duration of action of ropivacaine, when injected at the nerve root level during an interscalene brachial plexus block, is not available.

Therefore, a careful examination of onset times and duration is necessary to determine the optimal concentration and to determine whether increasing the concentration is clinically beneficial. The aim of this study was to compare the use of bupivacaine 0.5%, ropivacaine 0.5%, and ropivacaine 0.75% for an interscalene brachial plexus block for shoulder surgery.

Methods

Approval for the study was obtained from our institutional review board. Seventy-five patients classified as ASA physical status I-III, aged >or=to18 yr, gave written, informed consent to participate in this randomized, double-blind trial. All patients were scheduled for outpatient shoulder surgery, including open and closed procedures, under interscalene block. Patient exclusion criteria included coagulopathy, infection at the site of block placement, or hemidiaphragmatic paralysis contralateral to the side of surgery.

Patients were randomly assigned to receive 30 mL of one of three different solutions (n = 25 per group). All solutions contained fresh epinephrine in a 1:400,000 concentration as an intravascular marker. Group 1 received 0.5% bupivacaine, Group 2 received 0.5% ropivacaine, and Group 3 received 0.75% ropivacaine.

All patients were brought to the preoperative holding area and monitored using standard ASA monitors. Patients were sedated with IV midazolam (1-5 mg) and fentanyl (50-250 [micro sign]g), titrated to moderate sedation (arousable on command). All interscalene blocks were performed using the approach previously described by Winnie ^[3]. Using a 22-gauge, 50-mm, insulated, blunt needle (Braun Medical, Bethlehem, PA) and a nerve stimulator, a stimulus was sought distal to the shoulder. After an appropriate stimulus was localized with a current <0.5 mA, 30 mL of the study solution as injected in 3-mL increments. An intercostobrachial block was then performed separately to provide anesthesia for the possible placement of an anterior portal during shoulder arthroscopy ^[4].

Immediately after block placement, patients were evaluated every 1 min, by a clinician unaware of the injected solution, to determine loss of shoulder abduction (deltoid sign) as evidence of a successful motor blockade ^[5]. In addition, sensory block was assessed by pinprick every 1 min in the C5-6 dermatomes. Loss of pinprick sensation in the deep cervical plexus (C2-4) was documented as absent or present before skin incision. Failure to lose shoulder abduction after 30 min was considered to be a block failure. These patients were reblocked at the discretion of the attending anesthesiologist and omitted from statistical analysis. All episodes of local anesthetic toxicity or hemodynamic change requiring anesthesiologist intervention (increased IV fluids or inotropes) were recorded as adverse events. After evidence of a successful sensory and motor block, the patient was taken to the operating room for surgery. During surgery, additional infiltration of local anesthetic was not performed.

At the conclusion of surgery, all patients were transferred to the PACU and reassessed to confirm sensory and motor blockade. The patient and evaluator who conducted the postoperative follow-up were also unaware of the identity of the injected solution. Because all patients left the ambulatory unit, direct assessments were not possible after discharge. Instead, to evaluate sensation, patients were asked to document the time of first oral narcotic, the time when incisional discomfort began, and the time when full sensation returned to the shoulder. Data were obtained by telephone contact 48 h after block placement (patients were not phoned during the night).

Descriptive statistics for onset and duration were produced, including mean +/- SD. Standard normal theory was used to calculate 95% confidence intervals for pairwise differences between each pair of local anesthetic concentrations. These intervals convey the statistical significance (confidence intervals that do not include zero imply significance at the 0.5 level) as well as the variability in measures.

Results

There were no differences in age, weight, gender, or ASA classification among the groups (Table 1). Five different attending anesthesiologists and 10 different residents performed the blocks. After 30 min of evaluation, there were seven failed blocks in the study. Three failures occurred each in the 0.5% bupivacaine and the 0.5% ropivacaine groups. There was one failure in the 0.75% ropivacaine group. One patient in the 0.5% ropivacaine group with a successful block requested to withdraw from telephone screening and hence was omitted from analysis. This left a sample size of 21, 22, and 24 participants, respectively.

Table 1: Patient Characteristics

The mean onset time of motor block (loss of shoulder abduction) and sensory block (by pinprick) is depicted in Figure 1. In all three groups, mean onset time of sensory block was <6 min. The onset of motor and sensory block was not statistically different among the groups. Potential differences in these times among groups are demonstrated by the 95% confidence intervals for the pairwise differences, which are shown in Table 2. Pairwise confidence intervals all have a range <4 min, which indicates that any undetected differences are likely to be small. All patients with a successful block had loss of pinprick sensation over the dermatomes of the deep cervical plexus (C2-4) before skin incision. In addition, there were no adverse events in the three groups requiring intervention by the anesthesia team.

Figure 1: Time to onset of interscalene block in shoulder surgery patients treated with 30 mL of 0.5% bupivacaine, 0.5% ropivacaine, or 0.75% ropivacaine. Onset of motor blockade was defined as the interval from injection of local anesthetic until loss of arm abduction (A). Onset of sensory blockade was defined as time to loss of sensation to pinprick in the C5 (B) and C6 (C) dermatomes. There was no difference among groups for time to onset for any parameter. [large circle] = values for individual patients. Horizontal bars depict group means.

Table 2: 95% Confidence Intervals for Pairwise Differences

The times until first oral narcotic, onset of incisional discomfort, and return of full sensation of the shoulder are presented in Figure 2. Full sensation of the shoulder occurred at times similar to onset of incisional discomfort. The largest difference observed was for return of shoulder sensation, when comparing 0.5% bupivacaine and 0.75% ropivacaine. As indicated by the confidence intervals, this difference could be as small as -1.8 or as large as 7.0 h (Table 2).

Figure 2: Time to recovery of interscalene block in shoulder surgery patients treated with 30 mL of 0.5% bupivacaine (n = 21), 0.5% ropivacaine (n = 22), or 0.75% ropivacaine (n = 24). At time of discharge from the postanesthesia care unit, patients were instructed to record time of (A) recovery of sensation in the shoulder, (B) onset of pain in shoulder, and (C) first use of pain medicine. Intervals from time of local anesthetic injection were then calculated. There were no differences among the local anesthetic groups for time to recovery as defined by these three variables. [large circle] = values for individual patients. Horizontal bars depict group means.

Discussion

The selection of the optimal long-acting local anesthetic and concentration for interscalene brachial plexus block must take into consideration the available anesthetics, the time to onset, duration of blockade, and side effects of each drug and dose. A drug that has a fast onset, long duration, and minimal toxicity profile could be an advantage. Introduced recently, ropivacaine offers an alternative to bupivacaine for long-acting neural blockade. In a clinical practice, the choice and concentration of long-acting local anesthetics is only partially defined. No comparison of these two drugs has been made for interscalene block.

The results of this study suggest that 0.5% bupivacaine, 0.5% ropivacaine, and 0.75% ropivacaine each provide a fast onset time when evaluating shoulder abduction and loss of pinprick sensation in the C5 and C6 dermatomes. These criteria are essential for shoulder surgery performed under regional anesthesia. In fact, all three groups had a mean onset time for sensory block of <6 min. Based on this evaluation, there seems to be little clinical advantage for selection of one local anesthetic over the other based on the time to onset of neural blockade.

The duration of sensory block was more difficult to test because patients were discharged from the hospital before resolution of neural blockade. However, the time until first oral narcotic use, onset of incisional discomfort, and return of full sensation of the shoulder, as defined by the patient, were similar among groups. These measures corresponded to a duration of analgesia between 12 and 15 h. Despite the fact that there was no statistical difference among groups, all measurements of analgesic duration were associated with large confidence intervals because of the broad range of responses inherent in this type of technique and data collection. Therefore, a subtle difference could not be ruled out from this sampling size. However, all three groups did have similar response times for sensory duration. Because each local anesthetic provided long-acting analgesia with a mean time >12 h, there seems to be no clinical advantage of any one local anesthetic based on these data and the duration of analgesia.

The data from this study reveal a time to onset for motor blockade similar to that of Hickey et al. ^[6], who compared bupivacaine 0.5% with ropivacaine 0.5% for subclavian perivascular block. Onset of motor blockade was between 7 and 9 min at the shoulder, with no statistical difference between the two groups. However, time to loss of sensation at the C5 and C6 dermatomes was substantially longer (28-58 min) compared with that in our study.

These differences may be attributable to the anatomic location of the different nerve blocks (i.e., interscalene versus subclavian perivascular) and the technical procedures used. During an interscalene brachial plexus block, local anesthetic is injected at the level of the nerve roots. It has traditionally been the block of choice for shoulder surgery involving the C5 and C6 dermatomes. Although the subclavian perivascular block is one of the fastest in onset, it involves the injection of local anesthetic at the level of the nerve divisions and may account for part of the difference in the two studies. This difference in anatomic location is evident when comparing the frequency of analgesia in the cervical plexus dermatomes, C2-4, in this study with the frequently intact cervical plexus after a subclavian perivascular block. In addition, in our study, accurate needle localization was determined by motor response to a nerve stimulator compared with elicitation of parasthesias, as used by Hickey et al. ^[6]. This variation in technique may, in part, account for the differences in time to onset of sensory blockade.

In conclusion, there was no clinical difference in onset and duration among 0.5% bupivacaine, 0.5% ropivacaine, and 0.75% ropivacaine when injected in equal volumes for interscalene brachial plexus block. The fact that increasing the concentration of ropivacaine from 0.5% to 0.75% failed to improve onset or duration suggests that the risk of increasing the total milligram dose of local anesthetic may not be warranted. In addition, because there seems to be the same efficacy between equal concentrations of ropivacaine and bupivacaine, the choice of local anesthetic for shoulder surgery should not be based on onset and duration times alone. Because ropivacaine has a potentially improved safety profile compared with bupivacaine, it may offer an advantage.

The authors are grateful to Cynthia Shimer, BS, for her expert technical assistance.