Anesth Analg 2002;95:1075-1079
© 2002 International Anesthesia Research Society
REGIONAL ANESTHESIA
Four-Injection Brachial Plexus Block Using Peripheral Nerve Stimulator: A Comparison Between Axillary and Humeral Approaches
Salvatore Sia, MD,
Antonella Lepri, MD,
Maria Consolata Campolo, MD, and
Rossana Fiaschi, MD
Department of Anesthesiology, Centro Traumatologico Ortopedico, Azienda Ospedaliera Careggi, Firenze, Italy
Address correspondence and reprint requests to Salvatore Sia, Via Santelli, 41, 50134 Firenze, Italy. Address e-mail to sia3{at}interfree.it
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Abstract
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We conducted this prospective, randomized study to compare the success rate, performance time, and onset time of surgical anesthesia of a four-injection brachial plexus block performed at the axillary (Group Axillary; n = 50) or at the humeral (Group Humeral; n = 50) level using a peripheral nerve stimulator. All patients received 40 mL of a mixture of equal parts of 0.5% bupivacaine and 2% lidocaine. Four patients in Group Axillary and two in Group Humeral were excluded from the study because all of the four nerves were not localized in the allotted time. The incidence of complete block (91% versus 89%), defined as block of all the sensory areas below the elbow, and the onset time of sensory block (15 ± 6 min versus 16 ± 7 min) were not different between the groups. The performance time was shorter in Group Humeral (7 ± 2 min versus 8 ± 2 min; P < 0.005). Block performance pain was lower in Group Axillary patients (16 ± 9 min versus 23 ± 12 min; P < 0.005). For four-injection brachial plexus block, we conclude that both the axillary and the humeral approaches provide a high success rate and a rapid onset of sensory anesthesia; the differences found between the groups could be considered clinically unimportant.
IMPLICATIONS: Two methods of brachial plexus block using a nerve-stimulator were compared in a prospective study. A four-injection technique was performed at the axillary or at the humeral level. Both approaches provided a fast onset and a high success rate. The differences found between the groups could be considered clinically unimportant.
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Introduction
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The technique of multiple nerve blocks at the humeral canal with a neurostimulator (humeral block) was described in 1994 by Duprè (1). This approach provides a selective block of each major nerve from the brachial plexus and results in a high success rate (2–5). The only controlled study comparing the humeral block with a conventional axillary block was conducted by Bouaziz et al.(2) who found that the former approach provided a greater success rate than the latter (88% versus 54%). However, they compared a four-injection technique at the humeral level with a two-injection axillary block in which only the musculocutaneous and another nerve innervating the surgical site were located and injected. Several studies performed at the axilla demonstrated that a four-injection technique produced a rapid onset and frequent success (6–10).
On the basis of these results, we thought that a comparison between the technique of Duprè and a four-injection axillary approach would be more valid. Therefore, we conducted this prospective, randomized study to compare the onset time and the success rate of a four-injection technique performed at the axillary or at the humeral level.
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Methods
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After written informed consent and institutional human investigation committee approval, 100 ASA physical status I and II patients, scheduled for elective surgery of the hand, wrist, or forearm, were included in the study. All patients received fentanyl 1 µg/kg and midazolam 20 µg/kg IV 5 min before the block. The patients were randomly assigned to one of the following two groups: Group Axillary (n = 50) and Group Humeral (n = 50). The patients were placed supine with the arm abducted 90 degrees and bent at the elbow with the forearm supinated. A mixture of equal parts of 0.5% bupivacaine and 2% lidocaine was used. The subcutaneous tissue overlying the artery was infiltrated with 4 mL of the solution before the block to anesthetize the medial cutaneous nerves of the arm and forearm. A 22-gauge, 50-mm-long, short-bevelled insulated needle (Stimuplex; Braun, Melsungen, Germany) was connected to the negative lead of the nerve stimulator (Stimuplex). The stimulating current was set to 0.5 mA and the stimulus frequency to 2 Hz. In Group Axillary, the pulse of the axillary artery was palpated at the level of the major pectoral muscle crossing the axilla, and the needle was inserted superior to the artery to locate the median and the musculocutaneous nerves and inferior to locate the radial and the ulnar nerves. In Group Humeral, a humeral block was performed, according to the technique of Duprè (1), at the junction between the upper and the middle thirds of the arm. In both groups, 10 mL of the solution was injected for the median, radial, and ulnar nerves, and 6 mL for the musculocutaneous nerve. A maximum of 5 min was allowed to locate and perform injections for each nerve. All blocks were performed or supervised by the first author and assessed by a blinded investigator. Pain associated with the injections was assessed after completion of the block using the visual analog scale (VAS). Patients of both groups in which all of the four nerves were not localized were excluded from the study. The time to perform the block was defined as the time between the initial insertion of the needle to infiltrate the subcutaneous tissue overlying the artery and the removal of the insulated needle. The sensory block was assessed in the areas supplied by the six nerves of musculocutaneous (radial side of forearm), radial (radial side of the dorsum of the hand), median (thenar eminence), ulnar (fifth finger), medial cutaneous nerves of the arm (ulnar side of the arm), and of the forearm (ulnar side of the forearm) at 5, 10, 15, 20, 25, and 30 min after the end of the procedure. Sensory loss was assessed with the end of a 22-gauge needle. The block was defined as complete when loss of pinprick sensation was observed at 30 min in all the sensory areas below the elbow. In patients in whom a complete block was achieved, the onset period was measured between the end of the block performance and the onset of a complete sensory block. Motor block was assessed at 30 min and defined as either complete (no movements against gravity), satisfactory (minor movements of the digits possible), or absent. After 30 min, in case of incomplete block, the unblocked nerve(s) implicated in the surgical site were blocked at the elbow or wrist level. Midazolam, in 1-mg increments, was given IV to patients who requested sedation during surgery. Fentanyl, in 50-µg increments, was given IV in case of tourniquet pain. The incidence of adverse effects was noted. The incidence of acute nerve injury was evaluated at 48 h. Neurological sequelae were recorded during the surgical follow-up visits at 10 and 30 days.
To calculate the sample size of our study, we assumed that a 20% difference in success rate would be considered clinically important. To compare the two groups with a power of 80% to detect a 20% difference in success rate at a significance level of <0.05, the sample size required was 45 patients in each group. We enrolled 50 patients in each group to allow for dropouts. Data were analyzed using SPSS 8.0 for Windows (SPSS Inc, Chicago, IL) and Power and PrecisionTM (Biostat Inc, Englewood, NJ) software packages. Parametric variables were described as mean ± SD, qualitative variables as number (percentage), and VAS scores as median and ranges. Student’s t-test, Fisher’s exact test, or Mann-Whitney U-test was used as appropriate to compare the two groups. P < 0.05 was considered significant.
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Results
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Initially, 100 patients were included in the study. Four patients in Group Axillary and two in Group Humeral were excluded from the study because all of the four nerves were not localized in the allotted time. In particular, the four patients in Group Axillary were excluded because the ulnar nerve could not be located in 5 min. There were no demographic differences between the patients excluded and those with successful completion of the block. Group Axillary (n = 46) and Group Humeral (n = 48) were similar with respect to age (43 ± 14 yr versus 45 ± 17 yr), weight (68 ± 13 kg versus 70 ± 17 kg), men/women ratio (29:17 versus 28:20), surgical site (forearm/wrist/hand, 9/11/26 versus 9/8/31), duration of surgery (75 ± 28 min versus 69 ± 29 min), and tourniquet time (55 ± 25 min versus 57 ± 20 min). The block characteristics are shown in Table 1. The time to perform the block was significantly shorter in Group Humeral than in Group Axillary (7 ± 2 min versus 8 ± 2 min; P < 0.005). Median times were 8 min (range, 3–11 min) in Group Humeral and 9 min (range, 4–12 min) in Group Axillary. VAS scores at block performance were significantly lower in Group Axillary patients (16 ± 9 mm versus 23 ± 12 mm; P < 0.005). The onset period was recorded only in patients in whom a complete block was achieved at 30 min (42 patients in Group Axillary and 43 in Group Humeral). The onset of sensory block for the ulnar nerve was significantly shorter in Group Axillary than in Group Humeral (12 ± 5 min versus 15 ± 6 min; P < 0.05). Neither the onset time for the block of the other three main nerves nor the onset time for complete block were different between the groups. The spread of analgesia 30 min after the block was not different between the groups (Table 2). Three patients in each group underwent supplementary blocks. All but three patients in Group Axillary and four in Group Humeral required a tourniquet during surgery. None of the patients experienced pain from the site of surgery; however, two patients in Group Axillary and four in Group Humeral reported tourniquet pain. The amount of fentanyl administered to these patients did not differ between the groups (100 ± 0 µg versus 112 ± 62 µg). Three patients in Group Axillary and four in Group Humeral requested intraoperative sedation. The amount of midazolam administered to these patients did not differ between the groups (4 ± 1 mg versus 3.75 ± 1.26 mg). Symptoms of intravascular injection (dizziness, tinnitus, and perioral numbness) were observed in six patients (three in each group); no treatment was required for these patients. The axillary artery was punctured in two patients in Group Axillary and in one in Group Humeral. Accidental elicitation of paresthesia was observed in nine patients in Group Axillary and in seven in Group Humeral. Hematomas were noted in two patients in Group Axillary and in one in Group Humeral at the surgical follow-up. They were conservatively treated. Neurological complications were not observed in both groups.
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Discussion
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The aim of the present study was to compare two four-injection techniques of brachial plexus block performed at the axilla and at the humeral level. In four patients (8%) in Group Axillary and in two (4%) in Group Humeral one of the four nerves was not located in the allotted time. The incidence of lack-of-nerve stimulation for the humeral approach varied between 2% (5) and 12% (3) in previous studies. An 8% lack of nerve stimulation was reported with a four-injection axillary approach (8). We decided to exclude patients of both groups in which none of the four main nerves of the plexus were localized in the allotted time because we thought that the lack of stimulation of one or more nerves might have a different clinical effect on success rate in the two groups. In Group Humeral, where the nerves were well separated, localization of all of the four nerves was probably required to obtain a complete block, even if no study has been conducted to verify this hypothesis. Therefore, we thought that it would not have been correct to consider the two Group Humeral patients with lack-of-nerve localization into the statistical analysis to evaluate the success rate. However, we thought that it would not have been correct to consider as block failure the four Group Axillary patients in which the ulnar nerve was not located in five minutes. In fact, we previously found that a three-injection method of axillary block in which the ulnar nerve was not purposely located provided a spread and a latency of sensory block equal to that obtained with a four-injection technique (11). Therefore, we decided to include only patients of both groups in which all of the four main nerves of the plexus were localized in the allotted time and not to consider the remaining patients as block failures.
To standardize the criteria of success, we considered successful (complete block) only the blocks including the main four nerves to the forearm. For practical considerations, 30 minutes was arbitrarily chosen for the evaluation of the block, even if a delay might have extended the area of analgesia, thus affecting onset time as well as success rate.
A limitation of this study was its insufficient power to detect a difference in success rate between the groups. However, at this level of success (91% versus 89%), it is very difficult to show a statistical difference. In fact, to ensure a power of 80% for detecting a difference of 2%, 2782 patients had to be included in each group. The small clinical difference in success rate between the axillary and the humeral approach does not justify, in our opinion, the effort required to undertake such a large study.
The success rate was not different between the two groups (91% versus 89%) and was similar to that recorded in other studies using a four-injection axillary (6–11) or humeral (2–5) approach. The only study that compared the effectiveness of humeral (mid-humeral as defined by the authors) and axillary approach is that published by Bouaziz et al. in 1997 (2). They compared, using 1.5% lidocaine with epinephrine, the technique described by Duprè (1) with a two-injection axillary block on the basis of the results obtained by Lavoie et al.(12), who found that the stimulation at the axilla of the musculocutaneous nerve plus one of the other three major nerves of the plexus innervating the surgical site resulted in the same success rate as stimulation of all four major nerves. An incidence of complete block of 88% in the humeral group compared with 54% in the axillary group was reported (2). The authors stated that the midhumeral block results in more frequent success than a conventional axillary approach (2). Probably, it would have been better to conclude that a four-injection technique results in more frequent success than two-injection. In fact, the success rate obtained by Bouaziz et al. (2) in the axillary group was significantly different from that recorded by Lavoie et al. (12) (54% versus 94%), probably because of the different definition of successful block (block of the four major terminal nerves of the plexus versus sensory block of the surgical area). Analogous with the results of Bouaziz et al.(2), Coventry et al. (13) recently found that a double-injection technique, in which the median and the musculocutaneous nerves were located and injected, produced a complete sensory block in 53% of patients. These results are similar to those obtained with a single-injection axillary approach (6,14) and might suggest, in our opinion, that at least two injections near the brachial plexus sheath are required to obtain a satisfactory rate of complete block (14,15).
The time to perform the block was shorter in Group Humeral than in Group Axillary (7 ± 2 minutes versus 8 ± 2 minutes). However a difference of one minute in the mean performance time could be considered clinically unimportant. We think that the slightly longer performance time recorded in Group Axillary could be attributed to the longer time spent to localize the ulnar nerve that is difficult to locate at this level if the radial nerve is already located and injected. Localization of the ulnar nerve is probably easier at the humeral level where this nerve is anatomically apart from the radial nerve. Analogous with the results of the present study, the studies in which a four-injection technique was performed at the humeral level reported a shorter performance time than those in which the block was performed at the axilla. Humeral blocks took Kinirons et al. (16) and Bouaziz et al. (2) six minutes on average, Iskandar et al. (17) five minutes, and Bertini et al. (4) four minutes. Only Carles et al. (5) reported a performance time of 10 minutes. Koscielniak-Nielsen et al. (6,7) reported nine- and 10-minute performance times for axillary blocks. We previously found a performance time of eight minutes for blocks performed at the axilla using a four-injection technique (11).
No differences between the groups in onset time were found (15 ± 6 minutes versus 15 ± 7 minutes). The comparison of our onset times with those recorded by other authors is difficult because different local anesthetic solutions were used. Koscielniak-Nielsen et al. (7,8), using 1% or 2% mepivacaine with adrenaline for axillary block, reported a latency time (including supplementary nerve blocks) that varied between 20 and 10 minutes. The onset time reported by Bouaziz et al. (2), with a four-injection approach at the midhumeral level using 1.5% lidocaine with epinephrine, was 15 ± 10 minutes. Coventry et al. (13) showed that after a three-injection technique, in which 1.5% lidocaine with epinephrine was used, blocks were complete in 47% of patients at 10 minutes and in 90% at 20 minutes. The analysis of the onset times in the single neural distribution showed a significantly longer delay of the sensory block in Group Humeral for the ulnar nerve. A delay of the onset of the ulnar nerve block with the humeral approach was reported by Bouaziz et al. (2). We did not find the delay in the onset of sensory block of the median nerve recorded by Gaertner et al. (3). The shortest onset time was recorded for the musculocutaneous nerve in both groups, as reported by other authors (3,5).
The patients’ pain scores were significantly higher in Group Humeral than in Group Axillary (23 ± 12 mm versus 16 ± 9 mm). This might be explained by the more peripheral approach to the four nerves in which the musculocutaneous and radial nerves lie deeper than that in axilla. Our results are not in agreement with those reported by Kinirons et al. (16), who found in patients sedated with midazolam and sufentanil, pain scores of 14 ± 12 mm for the humeral approach. This discrepancy might be explained by a more effective sedation technique and by a significantly shorter performance time (5.7 ± 0.2 minutes versus 7 ± 2 minutes) recorded in the study by Kinirons et al.(16), which might indicate a reduced number of needle passes required to perform the block.
In conclusion, the differences found between the groups could be considered clinically unimportant. Both the axillary and the humeral approaches provide frequent success and a rapid onset without the need for elicitation of paresthesias or transfixion of the artery. Both techniques have its advantages. In axillary block, because the nerves are closely aligned, a reduced number of injections might be used (11,13,15). However, the approach at the humeral level, where the four nerves are anatomically well separated, allows for selective administration of different local anesthetic solutions on the various nerves. Therefore, it is possible to prolong the duration of sensory block in one or several trunks of the brachial plexus to provide postoperative analgesia targeted to the specific nerve distribution involved in the surgery while obtaining a complete block of the upper limb (17,18). Finally, it must be taken into consideration that the humeral canal is a perfect site to selectively block by nerve stimulation of one or more nerves after a failed axillary approach without the risk of inserting the needle near a partially anesthetized nerve. Therefore, we suggest that, even if axillary is the approach routinely used, anesthesiologists interested in upper limb blocks should be able to perform the humeral block.
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References
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Accepted for publication June 5, 2002.
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Abstract
Introduction
