Anesth Analg 2004;99:713-717
© 2004 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000129976.26455.32
AMBULATORY ANESTHESIA
A Comparison of Intrathecal Plain Solutions Containing Ropivacaine 20 or 15 mg Versus Bupivacaine 10 mg
Helena Kallio, MD PhD*,
Eljas-Veli T. Snäll, MD*,
Markku P. Kero, MD*, and
Per H. Rosenberg, MD PhD
*Department of Anesthesia, Forssa District Hospital, Forssa, Finland; and
Department of Anesthesiology and Intensive Care Medicine, Helsinki University Central Hospital, Helsinki, Finland
Address correspondence and reprint requests to Helena Kallio, PhD, Forssa District Hospital, PO Box 42, FIN-30101 Forssa, Finland. Address e-mail to helena.kallio{at}fstky.fi
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Abstract
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Ropivacaine, which blocks sensory nerve fibers more readily than motor fibers, is considered to be less potent than bupivacaine. Our hypothesis was that, when used in spinal anesthesia for day surgery, ropivacaine 15 and 20 mg would provide faster motor recovery than bupivacaine 10 mg. This prospective, randomized, double-blinded study included 90 ambulatory lower-extremity surgery patients who received 2 mL of ropivacaine 1%, ropivacaine 0.75%, or bupivacaine 0.5%. Motor block was tested with the Bromage scale, and sensory block was tested with pinprick. Ropivacaine 15 mg provided faster recovery of motor block (150 min) than did bupivacaine 10 mg (210 min; P = 0.005), but the median duration of sensory block at T10 (140 min) did not differ significantly from that with bupivacaine 10 mg (140 min). The median duration of sensory block at T10 was significantly longer with ropivacaine 20 mg (170 min) than with bupivacaine 10 mg (140 min; P = 0.005), but the median recovery from motor block (210 min) did not differ significantly. We conclude that the duration of sensory block of ropivacaine was two thirds and the duration of motor block was half when compared with bupivacaine, with calculations based on the duration-per-milligram of the local anesthetic.
IMPLICATIONS: In spinal anesthesia, ropivacaine provided two thirds of the duration in sensory block and half of the duration in motor block compared with bupivacaine. Both 20 and 15 mg of ropivacaine are suitable for lower-extremity surgery of 1 h in duration. The latter dose is preferable in day-case surgery because of rapid motor recovery.
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Introduction
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Ropivacaine came on the market in 1996 as the first pure S(–)-enantiomer of local anesthetics, and in certain countries—e.g., Finland, Sweden, and Switzerland—it has achieved an official indication for intrathecal use. Because of sensorimotor dissociation (1,2), ropivacaine should be a favorable local anesthetic for day-case surgery and could be associated with earlier postoperative mobilization than bupivacaine. This study was designed to compare plain solutions of ropivacaine 20 and 15 mg with bupivacaine 10 mg, supposing that patients could mobilize faster in both ropivacaine groups than in the bupivacaine group. The rationale for the dose selection was that the duration of action of ropivacaine in spinal anesthesia is approximately 50% (3) to 67% (4) that of bupivacaine. Plain bupivacaine 10 mg was regarded as an appropriate control because this dose is often used in spinal anesthesia for surgery of the lower part of the body.
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Methods
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The ethics committee of the institution approved the study, and all 90 patients gave their written, informed consent. Elective day-case minor lower-extremity surgery patients under spinal anesthesia were enrolled into the study. Inclusion criteria were body mass index 
35 kg/m2, height 155–192 cm, age 18–65 yr, and ASA physical status I–II. Randomization was performed by an envelope method with a stratification of 15 so that the anesthesiologist, surgeon, and the patient did not know group assignments. The patients were prospectively allocated into three groups: plain ropivacaine 1% (Naropin® 10 mg/mL, AstraZeneca AB, Sweden), plain ropivacaine 0.75% (Naropin 7.5 mg/mL; AstraZeneca AB), and plain bupivacaine 0.5% (Bicain® Spinal 5 mg/mL; Orion Pharma, Finland). In a blinded fashion, a 2-mL volume of each local anesthetic solution was injected intrathecally, corresponding to ropivacaine 20 mg, ropivacaine 15 mg, and bupivacaine 10 mg.
No premedication was given. The patients were continuously monitored with electrocardiograph and pulse oximetry. Noninvasive arterial blood pressure was recorded every 5–10 min in the operating room (OR), every 10–15 min in the postanesthesia care unit, and at least once in the day-case ward. Criteria for tachycardia, bradycardia, hypotension, and hypertension were any increase or decrease more than 20% from the baseline, but treatment was given only if clinically indicated (systolic blood pressure <80 mm Hg or heart rate <50 bpm). Before spinal anesthesia, 500 mL of acetated Ringer’s solution (Ringer®-Acetat Braun; B. Braun Melsungen AG, Melsungen, Germany) and fentanyl 1 µg/kg (Fentanyl® B. Braun 50 µg/mL; B. Braun) were given IV.
The patients were positioned in the lateral decubitus position with the operative side uppermost. A horizontal position of the spine was verified by using a spirit level. Infiltration anesthesia of the puncture site was performed with lidocaine 10 mg/mL (Lidocain® 10 mg/mL; Orion Pharma) with a 25-gauge Microlance® needle (Becton Dickinson, Ireland). Three anesthesiologists performed the spinal blocks, and their patients were distributed equally in the three study groups. The subarachnoid puncture was performed with a 27-gauge Whitacre pencil-point needle by using an introducer (Becton Dickinson, Spain) in the midline of the L3-4 interspace in 85 (94%) patients, but in cases of anatomy-related technical difficulties L2-3 or L4-5 was allowed. With the orifice facing cephalad, 2 mL of the plain anesthetic solution was injected over 20 s without barbotage or aspiration. Immediately after the puncture, the patient was placed supine, and at the same time the operating table was placed horizontally. A pillow was placed under the patient’s knees. All operations were performed with patients in the supine position.
An anesthesiologist who was blinded regarding which local anesthetic was used assessed sensory and motor block at timed intervals: 10, 20, 30, 45, 60, 90, 120, 150, 180, and 210 min after injection. In cases of any residual block, assessments were continued at 30-min intervals. The segmental level of sensory block to pinprick was assessed on both sides, and the caudal limit of sensory block testing was restricted to S2. Motor block of both legs was tested on the Bromage scale: 0, full movement; 1, inability to raise extended leg, can bend knee; 2, inability to bend knee, can flex ankle; and 3, no movement. If the sensory block was not adequate for the planned operation, general anesthesia was induced with propofol (Propofol-Lipuro® 10 mg/mL; B. Braun) and a laryngeal mask airway (The Laryngeal Mask Co. Ltd., Cyprus).
In the OR, ketoprofen 100 mg (Ketorin® 50 mg/mL; Orion Pharma) or propacetamol 2 g (Pro-Dafalgan® 1 g; Bristol-Myers Squibb, Sweden) was given IV. After the operation, all patients were allowed oral fluids, and the first intake was registered. The time of first spontaneous micturition and the time to reach discharge criteria were recorded by a ward nurse. The discharge criteria were the following: no breathing difficulties, stability of arterial blood pressure and heart rate, full orientation of the patient to time and place, ability of walking and dressing, ability of drinking without nausea or vomiting, micturition, and no more than slight pain. In addition, the actual time of discharge was registered. On the first postoperative day, a nurse interviewed the patients by telephone. Capability of moving, washing themselves, urinating, and defecating, as well as the occurrence of adverse effects (pain, nausea, vomiting, headache, backache, and other adverse symptoms), were registered.
Although the primary outcome variable was recovery from motor block, at the time this study started, other authors used other definitions of regression of motor block than the time to return to Bromage 0. Therefore, recovery of sensory block was used for power analysis (3). The ratio of the mean time (minutes) of 2-dermatome regression to the local anesthetic dose (milligrams) was 7 min/mg for bupivacaine and 4 min/mg for ropivacaine. Consequently, the mean time to 2-dermatome regression could be calculated to be 80 min with ropivacaine 20 mg, 60 min with ropivacaine 15 mg, and 70 min with bupivacaine 10 mg. The difference among all three means was 10 min, and the SD was estimated to be 15 min from the study of McDonald et al. (3). Because we chose an 
of 0.05 and a power of 0.95, we calculated the patient number to be 30 in each group.
In case of continuous numeric values, the mean ± SD are given, and the three groups were compared by using analysis of variance, but if the data were not normally divided, the Kruskal-Wallis test was used. Variables of order or rank were expressed as medians (interquartile range), and three groups were tested with the Kruskal-Wallis test. Binomial data are given in exact numbers in both categories combined with their percentages, and each two groups were compared with each another by 
2 or Fisher’s exact tests. Mean values of the right and left sides of each patient were used as basic data for testing sensory and motor block. Significant changes of sensory and motor block were tested within the groups with Wilcoxon’s test. Differences among the three groups in sensory and motor block assessments were tested by the Kruskal-Wallis test and between two groups with Mann-Whitney U-test. The variable minutes per milligram was used to compare ropivacaine with bupivacaine regarding the duration of sensory and motor block. When sensory onset and duration times of the block at the T10 dermatome were assessed, patients whose block did not reach T10 were excluded. A P value <0.05 was considered statistically significant. The statistics were calculated with SigmaStat® for Windows, version 2.03 (Jandel Corp.).
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Results
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The groups did not differ in demographic data or types of surgery (Table 1). The mean duration of the surgical procedures was 44 ± 22 min. The orthopedic surgeon infiltrated the wound region with a mean volume of 9 ± 5 mL of local anesthetic in 59% of the patients, and the groups did not differ significantly in this respect.
The groups did not differ in hemodynamics in the OR, postanesthesia care unit, or day-case ward (Table 2). The need for supplemental intraoperative IV sedation (32%) did not differ among groups. Six, 10, and 8 patients received additional fentanyl 62 ± 32 µg (mean ± SD) in the ropivacaine 20 mg group, the ropivacaine 15 mg group, and the bupivacaine 10 mg group, respectively. Seven patients were sedated with propofol 10–100 mg and 6 patients with diazepam 2.5–5 mg. General anesthesia was induced in 3 patients (one in each group) with propofol 150–250 mg, and a laryngeal mask airway was inserted. One patient in the bupivacaine 10 mg group needed general anesthesia because of an unexpectedly long (2.5 h) arthroscopy, which was converted to open knee surgery. One patient in the ropivacaine 20 mg group and 1 in the ropivacaine 15 mg group received general anesthesia because of insufficient sensory block.
Figure 1 shows the changes of sensory block in the three groups. In all groups, the median onset of analgesia to T10 was 10 min, and this was reached in 24 (80%), 21 (70%), and 24 (80%) patients in the three groups. If the time to reach the highest level of sensory block was measured from all study patients (n = 90), the median onset time was 30 min, with no difference among groups. The highest median extent of sensory block (n = 90) did not differ significantly among groups: T7 (T4–T10), T7 (T4–T12), and T9/T10 (T6–T11) in the ropivacaine 20 mg, ropivacaine 15 mg, and bupivacaine 10 mg groups, respectively. The median duration of analgesia at the level of at least T10 (n = 69; 24 + 21 + 24 patients) was 170, 140, and 140 min, respectively, and with ropivacaine 20 mg, the sensory block lasted significantly longer than with bupivacaine 10 mg (P = 0.005) or with ropivacaine 15 mg (P = 0.009). Consequently, the median sensory recovery to T10 counted from injection of local anesthetic was 180 min (9 min/mg), 150 min (10 min/mg), and 150 min (15 min/mg), respectively. The median time to 2-dermatome regression (n = 90) did not differ significantly among groups: 90 min (60–113 min), 90 min (49–100 min), and 70 min (60–100 min), respectively, in the ropivacaine 20 mg, ropivacaine 15 mg, and bupivacaine 10 mg groups.
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Figure 1. Pinprick sensory block is expressed as median values, which were assessed at 10, 20, 30, 45, 60, 90, 120, 150, 180, and 210 min from injection of local anesthetic. Statistical significance within the groups was tested with Wilcoxon’s test and between two groups with the Mann-Whitney U-test. The ropivacaine 20 and 15 mg groups did not differ in the 10- to 150-min period. The ropivacaine 15 mg and bupivacaine 10 mg groups did not differ in the 10- to 180-min period. The ropivacaine 20 mg and bupivacaine 10 mg groups did not differ in the 10- to 45-min period. Within the ropivacaine 20 mg group, there was no significant difference at 30–45 min, within the ropivacaine 15 mg group at 30–60 min, or within the bupivacaine 10 mg group at 30–45 min. All other comparisons between or within the groups resulted in a statistically significant difference.
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Motor block (n = 90) on the Bromage scale is shown in Figure 2. The median onset of complete motor block was 20 min, with no significant difference among groups. The median duration of complete motor block was 100, 40, and 100 min, respectively, in the ropivacaine 20 mg, ropivacaine 15 mg, and bupivacaine 10 mg groups. The median offset of motor block was significantly faster in the ropivacaine 15 mg group, and this reached full recovery in 150 min, compared with 210 min in the ropivacaine 20 mg (P = 0.014) and 210 min in the bupivacaine 10 mg (P = 0.005) groups.
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Figure 2. Bromage scale motor block is expressed as median values, which were assessed at 10, 20, 30, 45, 60, 90, 120, 150, 180, and 210 min from injection of spinal block. Statistical significance within groups was tested with Wilcoxon’s test and between two groups with Mann-Whitney U-test. The ropivacaine 20 mg and bupivacaine 10 mg groups did not differ significantly at any time, and the other two comparisons did not differ at 10–60 min. Within the ropivacaine 20 mg group, there was no difference at 20–120 min, within the ropivacaine 15 mg group at 20–60 min, or within the bupivacaine 10 mg group at 20–90 min from block injection. All other comparisons resulted in a significant difference.
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There was no difference in the recovery variables or home-readiness among groups (Table 3). Nineteen patients (21%) were hospitalized after the operation, and these patients were equally divided among groups. Seventeen patients had much more advanced surgery than planned beforehand, and these patients had to be hospitalized for postoperative surgical care. One patient stayed for social reasons. One patient in the ropivacaine 20 mg group stood up when the motor block had not totally disappeared. Her nonoperated right leg did not support her, and she collapsed. Her lower back was struck by lancing pain radiating to the right buttock. The patient was discharged the same evening, and the lumbago-type aching and pain disappeared within 5 days.
On the first postoperative day, 81% of the discharged patients, equally distributed among the three groups, responded to a postoperative telephone interview. One patient in the bupivacaine 10 mg group complained of back pain at the puncture site. Two patients in the ropivacaine 15 mg group complained of headache, which had ended by the evening of the day of operation. In the ropivacaine 20 mg group, one patient complained of a slight headache, but this was managed with a nonsteroidal antiinflammatory drug.
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Discussion
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Ropivacaine 15 mg provided faster recovery from motor block but a similar duration of sensory block compared with bupivacaine 10 mg. With ropivacaine 20 mg, the duration of sensory block was longer than with bupivacaine 10 mg, but the duration of motor block was similar. Ropivacaine 20 and 15 mg provided adequate anesthesia for lower-extremity surgery lasting approximately 1 hour. According to our hypothesis, ropivacaine 20 and 15 mg should have provided faster motor recovery than bupivacaine 10 mg, but only with the latter was this achieved. As seen in Table 3, the patients met our discharge criteria rather late, i.e., approximately six hours after the induction of spinal anesthesia. This did not create any problems, however, because in many instances the caretaking family member would not have been available earlier.
This study demonstrated that plain solutions of local anesthetics spread unpredictably, as noted previously (4,5). The median onset time was the same as the first assessment time, which makes this result somewhat unreliable. The assessment interval after 60 minutes was 30 minutes, which might also have decreased the sensitivity of the results, but this seems to have been compensated for by clear and statistically significant differences (low P values). As seen in our study, when we compared the durations of analgesia at the T10 dermatome, a block level sufficient for most operations performed under spinal anesthesia, ropivacaine 20 mg provided longer analgesia than bupivacaine 10 mg or ropivacaine 15 mg, but these did not differ from each other. Our result of ropivacaine having two thirds the duration of sensory block compared with bupivacaine is in accordance with earlier studies (4,6), whereas some other studies state approximately half (3,7–9) or an 86% duration of action (10). Our result of at least T10 sensory block duration of 9 to 10 min/mg of ropivacaine is similar to that of McNamee et al., i.e., 9 to 12 min/mg (10,11).
The comparison of the duration of complete motor block of the lower extremities also confirms that ropivacaine is approximately 50% less potent than bupivacaine, because a similar median duration was seen with ropivacaine 20 mg and bupivacaine 10 mg. Again, from a practical clinical point of view, the smaller dose of ropivacaine, 15 mg, proved beneficial because recovery of the motor block was the fastest. Our results of half the motor block duration of ropivacaine compared with bupivacaine is in accordance with earlier studies (7,8,10), whereas in other studies longer durations are also reported, e.g., two thirds (4) and three fourths (9). The recovery of motor block to a Bromage score of 0 with ropivacaine in our study was 10 to 10.5 min/mg. Earlier studies yielded results of the same magnitude, i.e., 7.2–12 min/mg (8,10,12–15).
Intrathecal, plain solutions containing ropivacaine 20 and 15 mg are suitable for ambulatory lower-extremity surgery of approximately one hour. The major advantage of ropivacaine 15 mg, in particular, is a faster motor recovery compared with bupivacaine 10 mg.
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Acknowledgments
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We thank our operating room faculty and day-surgery unit nursing staff, especially Raija Ceder, CRNP, who helped in collecting the patient data and taking care of the patients.
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References
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Accepted for publication April 5, 2004.
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Abstract
Introduction
