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*Leeds Teaching Hospitals, St. James’s University Hospital, Beckett Street, Leeds, England; and Specialist Registrar in Anaesthetics, Yorkshire Region, England
Address correspondence and reprint requests to Petronella R. M. Janzen, FRCA, Consultant Anaesthetist, Leeds Teaching Hospitals, St. James’ University Hospital, Beckett St., Leeds LS9 7TF, England.
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Abstract |
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Implications: This study compares two local anesthetics to determine which is most suitablefor day-stay upper-limb surgery under axillary brachial plexus block.Prilocaine 1% is more suitable than ropivacaine 0.5% because of a moreprolonged duration of action of ropivacaine, although this could be useful inother circumstances.
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Introduction |
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Prilocaine 1%, 0.5 mL/kg has been used successfully by Dunlop et al. (1) in a series of 178 patients undergoing hand surgery. Ropivacaine is an amide local anesthetic similar to bupivacaine but with a lower cardiotoxic potential (2,3). Previous studies have evaluated ropivacaine for brachial plexus anesthesia with the perivascular subclavian route (4), the interscalene route (5), and the axillary route (6–9). Most studies concentrated on comparing ropivacaine and bupivacaine (5–9) and found no statistically significant differences between the two. There does seem to be a larger degree of separation between motor and sensory blockade with ropivacaine at concentrations of 0.3% or less for the epidural route (10). A similar result for brachial plexus block has not been found.
This study compares ropivacaine and prilocaine for day-stay surgery, aiming to compare the onset time of sensory blockade and the offset of both sensory and motor blockade of the two drugs.
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Methods |
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All patients underwent upper-limb day-stay surgery. IV access was established in the contralateral arm. After skin infiltration over the axillary artery with 1 mL of study drug, the brachial plexus was located with a plexus needle (Pole needle; TOP Corporation, Tokyo, Japan) and nerve stimulator (Stimuplex; B. Braun, Franklin Lakes, NJ) by using a current of 0.6 mA or less, impulse width 93 µs. The same anesthetist performed all but three of the brachial plexus blocks. Twenty-five milliliters of study drug (prilocaine 1% or ropivacaine 0.5%) was injected at one site, and the remainder, giving a total of 0.7 mL/kg, was injected after relocation of the brachial plexus. Location end points were either paresthesia or, more usually, motor activity in the hand. In locating the stimulation end points for injection, we did not target specific nerves relevant to the operation site. The observer was blinded as to which local anesthetic was used.
The sensory block was tested by response to cold and skin pinch, with a score of 0 indicating normal sensation, 1 indicating analgesia (i.e., loss of sharp and cold sensation), and 2 indicating anesthesia (i.e., loss of sensation of touch). Sensory block was determined for the different innervation areas of the ulnar, median, radial, musculocutaneous, medial antebrachial cutaneous, and medial brachial cutaneous nerves.
Motor block was assessed by the patient’s ability to extend the flexed elbow and by wrist and hand movement in the radial, median, and ulnar nerve distribution areas. A score of 0 indicates no motor block, 1 indicates partial block, and 2 indicates complete block.
Zero time for clinical assessments was taken as time of completion of the injection. Assessments were made at 10, 20, and 30 min after completion of the block, then at 15-min intervals until the commencement of surgery or complete anesthesia and motor block. If after 45 min the block was deemed to be inadequate for surgery, an additional nerve block or blocks were performed with lidocaine at the wrist or elbow, as appropriate.
Patients were asked to assess the offset of motor block, anesthesia (sense of touch), and analgesia (sense of pain) themselves and to write down the respective times on a form they received after surgery (Appendix 1). They received a telephone call the next day to collect further data, such as pain, satisfaction scores, and the need for analgesia (dihydrocodeine 30 mg and acetaminophen 500 mg).
The onset and duration of block were compared with Student’s t-tests. All tests were two-tailed, and a P value of 
0.05 was considered significant. The primary outcome measure was time to onset of sensory block, and we considered a clinically relevant difference to be 10 min. The SD for onset time (from previous studies) is approximately 12.5 min (6,8,9,11). For a power of 80%, we required 26 patients in each group. Therefore, we decided to aim for 30 patients in each group to allow for the possibility of differences in variability in our population and patient dropout. For the secondary outcome measure—duration of motor block—we considered a clinically important difference to be 3 h, which gives a power of >95% with 30 patients.
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Results |
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The type of surgery performed is presented in Table 1. All patients underwent surgery successfully, and no sedation, IV analgesia, or general anesthesia was required. Supplementary injection of local anesthetic was required in 8 of 28 (29%) patients in the Prilocaine group and in 7 of 32 (22%) patients in the Ropivacaine group (not significant). This brings the total need for supplementary local anesthetic to 25%, most of which was administered by the surgeon. Patients were analyzed with intention to treat. One patient had a convulsion after completion of the block because of what was probably a partial IV injection. A further two patients possibly had IV injections; both were drowsy but did not develop further complications. There was no clinical evidence of methemoglobinemia.
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Discussion |
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This study was performed to compare the relative merits of ropivacaine and prilocaine for day-case patients undergoing hand and arm procedures under axillary brachial plexus block. It was hoped that ropivacaine would provide longer-lasting pain relief with less motor blockade. This, however, was not evident in our group of patients. We expected the onset of ropivacaine to be slower than prilocaine, but this was not the case. As far as onset time of sensory block is concerned, there was no difference between the two drugs at 20 minutes, and the slight differences at 10 minutes would not be clinically useful. The motor block continues to get denser after 20 minutes.
We used a large volume of local anesthetic, which we believe was a major factor in increasing the rate of satisfactory block. The need for additional nerve blocks in the study of Dunlop et al. (1) was 34%. This rate is similar to that in a study comparing bupivacaine and ropivacaine in concentrations of 0.5% at doses of up to and more than 3 mg/kg (7). Their rate of additional nerve block is more than in our practice, where the need for additional local anesthetic is approximately 15% to 20%, although in this study it was 25%. The double-injection technique results in a better quality of the block (12,13).
Because we considered that using different volumes of local anesthetic drugs to be tested would prejudice results, we decided to look at the safety aspects of using a similar volume of 0.5% ropivacaine to that used of prilocaine. Studies comparing the acute toxicity of ropivacaine to that of bupivacaine found that ropivacaine was at least 25% less toxic than bupivacaine with regard to the tolerated dose (2), with the threshold for central nervous system toxicity for ropivacaine twice that of bupivacaine (3). Other studies have used a maximum dose of ropivacaine and bupivacaine of >3 mg/kg without any toxic side effects (4,5,7). Peak plasma concentration depends on other variables, as well as body weight, and in particular it is accepted that the maximum safe doses of local anesthetic differ according to the injection site. Local anesthetics are only slowly absorbed after injection for axillary plexus block. A dose of ropivacaine of 3.5 mg/kg would therefore not be expected to cause toxicity because of total dose absorption, being <25% larger than doses of bupivacaine used safely in previous studies (7). We therefore chose 0.7 mL/kg of either drug in this study, or 3.5 mg/kg of ropivacaine and 7 mg/kg of prilocaine.
The addition of epinephrine to ropivacaine did not alter pharmacokinetic properties (14), and we therefore chose plain ropivacaine. Ropivacaine has mildly vasoconstrictive properties of its own (15).
Bertini et al. (9), by using 32 mL of local anesthetic, found similar efficacy between equal concentrations of bupivacaine and ropivacaine, with no improvement of onset time or duration of action when comparing 0.5% bupivacaine with 0.75% ropivacaine for axillary plexus block, although onset time with ropivacaine was faster than with bupivacaine. The mean onset time of sensory blockade was >16 minutes for axillary plexus block in their study, and the quality of anesthesia was better with ropivacaine.
This is in contrast to the study by Raeder et al. (8), in which, although increasing the concentration did improve the quality of block via the axillary route, there was no difference in onset time or duration of block. Raeder et al. found that ropivacaine 0.75% produced axillary brachial plexus blockade of superior quality when compared with bupivacaine 0.5%. The dose of ropivacaine used was 300 mg. Because the relative potency of ropivacaine and bupivacaine has been reported as 97% for sensory block and 84% for motor block in the isolated rabbit nerve model (16), it might be expected that ropivacaine 0.75% would produce a denser sensory block than bupivacaine 0.5%.
Vainionpaa et al. (7) compared 0.5% ropivacaine with 0.5% bupivacaine in axillary brachial plexus block and found no statistically significant differences in the clinical (and pharmacokinetic) comparisons. They had a need for an additional nerve block or blocks, supplemental analgesia, or general anesthesia in 38% (n = 29) of the Ropivacaine group and 36% (n = 31) of the Bupivacaine group. They used a slightly different dose of drug depending on patient body weight: 30 mL (weight <70 kg), 35 mL (weight 70–80 kg), or 40 mL (weight >80 kg), which is a smaller drug dose than that used in our study.
McGlade et al. (6) compared 0.5% ropivacaine with 0.5% bupivacaine for axillary brachial plexus anesthesia and found them to be equally effective, with bupivacaine producing a significantly longer duration of partial motor block at the wrist and hand. The requirement for supplemental blocks was 33% (n = 29) for the Ropivacaine group, compared with 22% (n = 32) in our study.
Prolonged motor block is inappropriate for day-case patients because it limits their ability to be self-caring after discharge. Prolonged analgesia is less important because pain should not be severe and should usually be easily manageable with simple analgesics.
This study has shown that prilocaine appears to be more suitable than ropivacaine for day-case anesthesia, although most patients had more satisfaction whichever local anesthetic was used.
Appendix 1. Patient Questionnaire
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