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REGIONAL ANESTHESIA AND PAIN MEDICINE

Multiple-Injection Axillary Brachial Plexus Block: A Comparison of Two Methods of Nerve Localization–Nerve Stimulation Versus Paresthesia

Department of Anesthesiology, Centro Traumatologico Ortopedico, Firenze, Italy

Address correspondence and reprint requests to Salvatore Sia, MD, Via Santelli, 41, 50134 Firenze, Italy.

	Abstract

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We conducted this prospective study to compare the onset time and the success rate of a multiple-injection axillary brachial plexus block performed by using two methods of nerve localization: paresthesia elicitation or nerve stimulation. Each of the major nerves of the plexus was located by elicitation of a paresthesia (Group PAR; n = 50) or by nerve stimulation (Group PNS; n = 50) and injected with 10 mL of local anesthetic solution. Time to perform the block, onset time of the primary block, time to achieve readiness for surgery, and total anesthetic time were significantly shorter in Group PNS than in Group PAR. The incidence of complete block was larger in Group PNS than in Group PAR (91% vs 76%; P < 0.05), and this was related to a larger success rate for anesthetizing the radial and the musculocutaneous nerves (P < 0.05). The frequency of venous puncture was larger in Group PAR (P < 0.05). For multiple-injection axillary brachial plexus block, we conclude that nerve stimulation resulted in a greater success rate and a faster onset than paresthesia elicitation, and it should be considered when the radial and musculocutaneous nerve distributions are involved in the surgical area.

Implications: Two methods of nerve localization were compared when performing an axillary brachial plexus block by the multiple-injection technique. Nerve stimulation provided a faster onset and a greater incidence of complete block, related to a better success rate for anesthetizing the radial and the musculocutaneous nerves, than paresthesia elicitation.

	Introduction

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When the single-injection technique is used, peripheral nerve stimulation is reported to be no more effective than single paresthesia elicitation in providing axillary brachial plexus blockade (1). However, a single-injection axillary block will only rarely anesthetize all the major branches of the plexus, and its success rate is not affected by the method of identification of the neurovascular compartment (1–4). Several clinical studies of axillary blockade have reported improved results when comparing multiple to single injections (4–6). The multiple-stimulation technique, in which the four main nerves of the plexus are localized at the axilla by a nerve stimulator and separately injected, was shown to provide a high success rate and a short onset time (4,7,8). We are not aware of previously published studies comparing the effectiveness of nerve stimulation and paresthesia elicitation when the four main nerves of the plexus are individually localized. Therefore, we conducted this prospective, randomized study to compare the onset time and the success rate of a four-injection technique performed using the neurostimulation or the paresthesia elicitation technique.

	Methods

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After we obtained written, informed consent and institutional approval, 100 ASA physical status I and II patients, scheduled for elective or acute surgery of the hand, wrist, or forearm under axillary brachial plexus block, were included in the study. No premedication was given. The patients were randomly assigned to one of the following two groups, according to the method of identification of the main nerves of the plexus (musculocutaneous, radial, median, and ulnar): in Group PAR (n = 50), the nerves were identified by elicitation of four separate paresthesia; in Group PNS (n = 50), the nerves were identified by four individual nerve stimulations. The patients were placed supine with the arm abducted 90° and the forearm placed in the supine position. The approach to the brachial plexus block was the same in both groups. The pulse of the axillary artery was palpated at the level of the major pectoral muscle crossing the axilla. 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. In Group PAR a 25-gauge, 3.8-cm, long-bevelled needle was inserted perpendicularly into the neurovascular sheath above the axillary artery to localize, by elicitation of paresthesia, the median nerve. The needle was then withdrawn and reinserted at the same level below the artery to localize the radial and the ulnar nerves. Ten milliliters of a mixture of equal parts of 0.5% bupivacaine and 2% lidocaine was injected through an extension tubing on each nerve. Ten milliliters of the anesthetic solution was injected into the substance of the coracobrachialis muscle to block the musculocutaneous nerve. In Group PNS, a 22-gauge 50-mm long, short-bevelled insulated needle (Stimulplex^®; Braun, Melsungen, Germany) was connected to the negative lead of the nerve stimulator (Stimulplex^®). The needle was inserted at the same level and with the same direction as in Group PAR: the median and the musculocutaneous nerves were located above the artery, the radial and the ulnar nerves below. The stimulating current was set to 0.5 mA and the stimulus frequency to 2 Hz. The nerves were located according to the specific motor-evoked activity as follows: musculocutaneous, arm flexion; radial, forearm and finger extension, supination; median, wrist, second and third finger flexion, pronation; ulnar, fourth and fifth finger flexion, thumb adduction. Four separate injections of 10 mL of the local anesthetic solution were made. In both groups, the blocks were performed with the aid of a second person who dialed the stimulator and injected the solution.

Patients of both groups in which all the three nerves innervating the hand were not localized were excluded from the study. All blocks were performed by the first author and assessed by a blinded investigator. The time to perform the block was defined as the time between the initial insertion of the needle and its removal. The sensory onset of the primary block was assessed in the areas supplied by six nerves: musculocutaneous (lateral side of forearm), radial (lateral side of the dorsum of the hand), median (thenar eminence), ulnar (fifth finger), and medial cutaneous nerves of the arm (medial side of the arm) and of the forearm (medial side of the forearm), at 10, 20, and 30 min after the end of the initial block. Sensory loss was assessed with the end of a 22-gauge needle and defined as analgesia (loss of pin-prick) or anesthesia (loss of touch). The primary block was defined complete when analgesia or anesthesia (surgical analgesia) was observed at 30 min in all the sensory areas below the elbow. After 30 min, in case of incomplete block, the unblocked nerve(s) implicated in the surgical site were blocked at the axilla, elbow, or wrist, and the sensory assessment continued 40 and 50 min after the primary block. The patient was declared ready for surgery when he/she had a complete block or, in case of incomplete block, surgical analgesia in all areas necessary for surgery. Latency time was considered the time between the end of the primary block and the time when the patient was pronounced ready for surgery. Total anesthetic time was calculated by adding the times for block performance and latency. Primary block effectiveness was calculated as the percentage of patients in each group in which a complete block was obtained at 30 min. Primary block was also separately assessed at 30 min for each nerve. Secondary block effectiveness was calculated as percentage of patients in each group who had surgical analgesia after supplementary blocks. Motor block was assessed at 30 min and defined complete (no movements against gravity), satisfactory (minor movements of the digits possible), or absent. 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. Patients were asked by an anesthesiologist at 48 h, by telephone if they were discharged before, to evaluate the incidence of acute nerve injury. Neurological sequelae were recorded during the surgical follow-up visits at 10 and 30 days. Patient comfort during the anesthetic procedure was evaluated at the end of surgery and graded as excellent, satisfactory, and unsatisfactory.

Parametric variables were described as mean ± SD and compared between groups with Student’s t -test. Qualitative variables were described as number (percentage) in each category and analyzed by using Fisher’s exact test. P < 0.05 was considered significant. All analyses were performed by using SIMSTAT statistical analysis package version 3.5 for DOS (Provalis Research, Montreal, Quebec, Canada).

	Results

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Of the 100 initially enrolled, one patient assigned to Group PNS and three assigned to Group PAR were withdrawn from the study because at least one of the three nerves innervating the hand could not be located. Demographics and type and duration of surgery were not significantly different between the groups (Table 1). The block characteristics are shown in Table 2. The time to perform the block, the onset of the primary block, the latency time, and the total anesthetic time were shorter in Group PNS than in Group PAR. Spread of surgical anesthesia after primary block is shown in Table 3. The higher rate of complete block in Group PNS patients was related to a higher success rate for anesthetizing the radial and the musculocutaneous nerves. Seven Group PAR and three Group PNS patients underwent supplementary blocks. None of the patients experienced pain from the site of surgery; however, five patients in Group PAR and three in Group PNS reported tourniquet pain. Fentanyl was administered to six patients, three in each group. Intraoperative sedation was requested by six patients in Group PAR and four in Group PNS. The incidence of venous puncture was higher in Group PAR than in Group PNS (Table 2). Symptoms of intravascular injection were observed in eight patients, four in each group. Accidental elicitation of paresthesia was observed in four patients in Group PNS. Patient comfort evaluation was not different between the groups (Table 2). Axillary hematomas were noted in four patients in Group PAR at the surgical follow-up (P = 0.53). They were treated conservatively. A paresthesia in the ulnar nerve area, unrelated to surgical site, was observed at the 48 h control in a Group PAR patient. The symptom resolved in 9 days.

	Discussion

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The success rate we observed in Group PNS is similar to that reported in previous studies using a four-stimulation technique (4,7,8). Group PAR’s overall success rate is difficult to compare with that recorded in previous studies using multiple-paresthesia research, because the number of elicited paresthesias and the success criteria are widely different (6,10). However, when the incidence of successful block for the individual nerve is analyzed, a general observation can be made: the nerves innervating the palmar area were blocked in all the studies with high percentages of success rate (6,10), whereas lower success rates were obtained in the block of the radial and musculocutaneous nerves. Baranowski and Pither (6) reported a success rate of 72% for the radial and 59% for the musculocutaneous nerve block. Rucci et al. (10) obtained a successful block of the radial in 76% of patients and of the musculocutaneous nerve in 60%. A success rate of 82% for the radial and of 85% for the musculocutaneous nerve block was obtained in the present study.

This is the first study in which a higher success rate was obtained by the use of a nerve stimulator when compared with the paresthesia method. The discrepancy between the results of the few previous studies comparing paresthesia elicitation to nerve stimulation and ours might be explained by the relevant differences between the protocols. Goldberg et al. (1) compared a single-paresthesia technique with a single-nerve stimulation and the transarterial approach, concluding that the success rates were no different. The lack of difference between the groups in this study might be explained by the limitations of the single-injection technique. The success rates of a single-injection axillary block are small and are not affected by the method of identification of the neurovascular compartment (1–5). This is not related to an insufficient proximal spread of the local anesthetic as initially postulated (11), but probably to an insufficient circumferential spread to the various nerves of the plexus (12,13).

The efficacy of the different methods of identification of the nerves in producing a successful block might be better shown in the multiple-injection technique, when the individual nerves of the plexus are located and injected with small volumes of local anesthetic, than in the single-injection technique, when a large volume of local anesthetic is injected in one point of the neurovascular compartment and must spread to all nerves of the plexus. Baranowski and Pither (6) showed that there was no difference in success rates between catheter, multiple-paresthesia, and multiple-stimulation techniques. In this study, one to three nerves were located; three nerves were located in only 12 patients in the paresthesia group and in 4 in the stimulation group. Baranowski and Pither (6) defined a block complete when three nerves were blocked at 30 min. In the present study, blockade of all four terminal nerves of the brachial plexus was required. Again, it might be hypothesized that, with the multiple-injection technique, the difference in efficacy of the nerve localization techniques in producing a successful block is better demonstrated. A possible explanation of our results may lie in the higher objectivity of the nerve stimulator in localizing the various nerves than paresthesia elicitation. The use of a nerve stimulator requires no input from the patients who, because of anxiety, fear or lack of knowledge, may not adequately report a paresthesia when one is sought (14).

The significantly shorter onset time in Group PNS patients suggests that the local anesthetic is being delivered closer to the nerves. Another important contribution to the faster onset of surgical anesthesia in Group PNS was the reduced need for supplementary blocks. The onset time of the primary block in Group PNS was similar to that recorded in other studies using the same technique (4,7,8). The shorter time for the block performance found in Group PNS can be explained by the easier localization of the four nerves and by the fact that no input from the patient is required. The time for block performance in Group PNS was shorter than in other similar studies (4,7,8), probably because the blocks were performed with the aid of a second person and the subcutaneous tissue overlying the artery was infiltrated before the block performance. The saving of nine minutes in Group PNS amounted to a 26% reduction in total anesthetic time.

The difference in the incidence of complete block was related to a larger success rate for anesthetizing the radial and the musculocutaneous nerves in Group PNS. A muscular response related to the stimulation of the musculocutaneous nerve was very easy to obtain in all the patients of Group PNS, whereas a blind injection into the body of the coracobrachialis muscle was used in the Group PAR. Even if a successful block of the musculocutaneous nerve was obtained in 85% of the Group PAR patients, we believe that the use of a nerve stimulator permits a more reliable and simple way of separately localizing and blocking the nerve, and this represents one of the main advantages of the technique. The different success rate in the two groups in blocking the radial nerve were more difficult to understand. This nerve was located in all the Group PAR patients. It might be that median and ulnar nerves, which lie in a more superficial plane, were more easily reached by the spread of the local anesthetic, even if the nerve localization had not been precisely made. Otherwise, the deeper position of the radial and musculocutaneous nerves might require a precise localization to obtain a satisfactory block in a large percentage of cases.

Many anesthesiologists are concerned about the increased theoretical risk of needle trauma with multiple-injection for axillary block. However, several studies reported no neurological complications after axillary brachial plexus block with multiple-stimulation technique (4,7,8). A recent observational study (15) demonstrated a 1.7% incidence of transient neurologic dysfunction after 3996 nerve blocks performed with a multiple-injection technique, which is similar to that reported by Selander et al. (16) with a single-injection technique. Therefore, the withdrawal and redirection of the stimulating needle does not seem to be associated with an increased incidence of nerve injury. The role of paresthesia in the development of nerve injury has not been well defined. Theoretically, the elicitation of a paresthesia during axillary block may represent direct needle-induced trauma and increase the risk of persistent nerve injury. There are no clinical studies that report a significant increase in nerve injuries related to elicitation of paresthesia, even with repeated blocks (17), although some authors conclude that nerve blocks should be performed without seeking paresthesias (6,18). Only a transient ulnar paresthesia was noted in Group PAR. Larger prospective studies are needed to identify the risk factors for anesthetic-related nerve injuries.

A significantly higher incidence of venous puncture was recorded in Group PAR; four axillary hematomas, treated conservatively, were noted in Group PAR at the surgical follow-up. Despite repeated aspiration tests and slow injections, four patients in each group showed signs of intravascular injections. The importance of carefully monitoring the patients, during and after the performance of the block, must be emphasized. Patient comfort evaluation showed no differences between the groups. However 21% of the patients in Group PAR and 14% in Group ENS showed a poor acceptance of the procedure, mainly because of the discomfort during the block placement. The lack of premedication and the withdrawal and redirection of the needle to localize all the nerves of the plexus might explain this result. Routine analgesic medication should probably be advocated when performing a brachial plexus block using the multiple-injection technique.

Several practical conclusions can be inferred from the results of this study. The multiple-injection technique using a nerve stimulator resulted in faster patient readiness for surgery and required fewer supplementary blocks than the same technique in which the localization of the nerve trunks is made by elicitation of paresthesia and, therefore, may be preferred when a rapid onset of the block is required. When surgery involves the palmar area, which the median and the ulnar nerves supply, both the techniques may be successfully used. In situations in which several nerves have to be blocked (especially if the radial and/or the musculocutaneous nerves are involved, as in the case of surgery of the wrist or of the forearm), a neurostimulator may be helpful.

In conclusion, when a four-injection technique for axillary brachial plexus block is used, the use of a neurostimulator resulted in a greater success rate and a faster onset than the elicitation of paresthesias.

	References

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999