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A variety of techniques have been described for the axillary block using nerve stimulator, either with single injection, two, three, or four separate injections. Identification of all the four nerves is more difficult and time-consuming than other methods.
Aim of the present study is to compare success rate, onset, and duration of sensory and motor anesthesia of axillary block using nerve stimulator, either with single injection after identification of any one of the four nerves or four separate injections following identification of each of nerve.
Prospective, randomized, double-blind study. Patients undergoing forearm and hand surgeries under axillary block.
One hundred patients, aged 18–75 years, were randomly allocated into two groups of 50 each. Axillary block was performed under the guidance of nerve stimulator with a mixture of 18 ml of 1.5% lignocaine and 18 ml of 0.5% bupivacaine. In the first group (n = 50), all 36 ml of local anesthetic was injected after the identification of motor response to any one of the nerves and in Group 2, all the four nerves were identified by the motor response, and 9 ml of local anesthetic was injected at each of the nerves. The success rate of the block, onset, and duration of sensory and motor block was assessed.
Categorical variables were compared using the Chi-square test, and continuous variables were compared using independent t-test.
The success rate of the block with four injection technique was higher compared to single-injection technique (84% vs. 56%, P = 0.02). Four injection groups had a faster onset of sensory and motor block and prolonged duration of analgesia compared to single-injection group (P < 0.001). There were no significant differences in the incidence of accidental arterial puncture and hemodynamic parameter between the groups.
Identification of all the four nerves produced higher success rate and better quality of the block when compared to single-injection technique.
Axillary brachial plexus block is one of the most widely used regional anesthesia technique for surgical procedure involving forearm, wrist, and hand. Ease of performance, presence of clear vascular landmark, and absence of major complications makes it a preferred block. However, the main limitation of the axillary block is variable success rate of the block. Many methods such as paresthesia, transarterial injections, and use of nerve stimulator or ultrasound guidance have been described. Previous studies have shown a higher success rate of the block and lesser complications when using a nerve stimulator compared to the transarterial injection or by paresthesia technique.[2,3] Many recent studies have demonstrated that ultrasound-guided axillary block provided similar success and complication rates as with nerve stimulation method.[4,5] Thus, equal efficacy and absence for the need of expensive ultrasound machine make nerve stimulator still an attractive method for axillary block.
Forearm and hand get their innervation from four nerves, namely, ulnar, median, radial nerve, and musculocutaneous nerves. The techniques described for axillary block using nerve stimulator are identification of one, two, three, or all the four nerves and corresponding number of separate injections.[6,7,8,9,10,11,12] Many studies suggest higher success with the identification of more nerves individually, but identification of all the four nerves is more difficult and time-consuming than other methods. However, a similar study has shown no significant difference in block success rate between three and four injections technique which implies that identification of ulnar nerve is not always essential. Therefore, a simplified technique with a reduced number of injections might be desirable.
The aim of this study is to compare the success rate, onset, and duration of sensory and motor anesthesia of axillary block using nerve stimulator, either with single injection after the identification of any one of the nerve or four separate injections following identification of all the four nerves.
After approval from the Hospital Ethical Committee, 100 patients in the age group of 18–75 years undergoing forearm, and hand surgeries were included in this prospective, randomized double-blind study. Informed consent was taken from all the patients. All patients of the American Society of Anesthesiologists (ASA) physical status classification I to III undergoing both elective and emergency forearm and hand surgeries planned under axillary brachial plexus block were considered for inclusion in this study. Patients who refused regional anesthesia or those with altered coagulation, infection at the site of injection, axillary lymphadenopathy, and those with hypersensitivity to amide local anesthetic drugs were excluded from the study. Patients were randomized into two groups by sealed envelope method. After the group assignment, a consultant anesthesiologist along with a resident performed the axillary block with either single injection or four injections method as determined by the envelope. Another anesthesiology resident, who was outside the operation theater when the block was being performed, assessed the success and onset of sensory and motor block. Patients were not aware of the number of nerves identified during the block performance; therefore, double blinding was ensured.
All patients received oral ranitidine 150 mg and ondansetron 4 mg in the morning of surgery. Patients were positioned in the supine position with shoulder abducted to 90° and elbow flexed to 90°, avoiding hyperabduction. After thorough skin preparation with aseptic precautions, axillary artery is palpated at the level of distal axilla. For patients belonging to Group 1 (n = 50), axillary block was attempted by single injection with 22-gauge nerve stimulator needle connected to peripheral nerve stimulator (Fisher and Paykel Innervater 252@™) at 1 mA current. The needle was inserted just above the axillary artery pulsations and after obtaining the motor response in any of forearm muscle, current was decreased up to 0.4 mA. After confirming motor response and negative aspiration for blood, all the 36 ml of local anesthetic solution was injected. For the other group, patient's arterial pulse was considered as center of a four quadrant neurovascular bundle. Conceptually, the musculocutaneous nerve is found in posterior superior quadrant (9–12 o’clock position to the artery) in the substance of the coracobrachialis muscle. The median nerve is most often found 12–3 o’clock quadrant; the ulnar nerve is inferior to median nerve in the 3–6 o’clock quadrant. Radial nerve is located slightly posteroinferior to the axillary artery. Needle insertion was done at the lower portion of the axilla, around the artery. A 22-gauge needle connected to peripheral nerve stimulator at 1 mA is inserted in the above-mentioned quadrants to locate the nerves. The nerves were located according to the specific motor-evoked activity as follows; radial nerve as wrist or finger extension, supination, median nerve as wrist, second and third finger flexion, pronation, ulnar nerve as flexion of fourth and fifth fingers, thumb adduction and that of musculocutaneous nerve as biceps contraction (arm flexion). All the four nerves were identified with the nerve stimulator and 9 ml of local anesthetic solution was injected at each of the four nerves. Local anesthetic used was a combination of 18 ml of 1.5% lignocaine and 18 ml of 0.5% bupivacaine for all patients. In Group 1, all of the local anesthetic was injected at only one place, whereas in Group 2, it was divided into four aliquots and deposited around four individual nerves. To assist tourniquet use, intercostobrachial nerve block was performed for all patients in both groups using 2 ml of 1.5% lignocaine.
Cutaneous analgesia for pinprick was assessed by blinded observer at 10, 20, and 30 min after the injection. Inability to move relevant muscle group against gravity was assessed for motor block. Intraoperative sedation was provided by the boluses of intravenous midazolam. If surgical anesthesia was inadequate after 30 min of the block, it was considered block failure and supplemented with intravenous fentanyl or general anesthesia (GA). Block performance time (defined as time from needle insertion to removal) was noted. The onset of sensory block was defined as the interval between local anaesthetic injection and the appearance of complete analgesia over the distribution of each major nerve. The success rate of block in each group was studied. Duration of sensory block was defined as the time between the onset of sensory block and time for appearance of surgical pain. The time for onset of motor block was the interval between local anaesthetic injection and the time when patient could not move the forearm muscles against gravity. Duration of motor block was the interval between onset of block and the time when the patient regains movement of forearm against gravity. Time to the first analgesic requirement in the postoperative period was noted. Intravenous tramadol 50 mg was given at this time. Hemodynamic parameters such as pulse, blood pressure were measured before the block, 5, 15, 30, and 60 min after the block. Any complications related to the procedures such as arterial puncture, venous puncture, and local anesthetic toxicity were noted.
Previous studies have shown the block success rate with single-injection technique as 54%. For an additional, 25% of improvement in the block success rate presuming an α error of 0.05 and to achieve 80% of power, 44 patients were needed in each group. The sample size was calculated using statistical software package provided by Medical University of Wien. Statistical analyses were performed using SPSS version 16.0 (SPSS Inc., Chicago, IL, USA). Categorical variables were compared using the Chi-square test or Fisher's exact test. Continuous variables were compared using independent t-test. Data are presented as mean and range or as the number of patients and percentages. P <0.05 was considered statistically significant and values P < 0.001 were considered very significant.
There was no significant difference in age, ASA status, and weight of the patients between the two groups [Table 1]. Type of surgeries and nature of surgeries performed also did not differ between the groups.
Among fifty patients in Group 1, 22 patients had inadequate surgical block and hence were converted to GA. Whereas in Group 2, among fifty patients, only eight had inadequate block and were converted to GA [Table 2]. Therefore, higher proportion of the patients had successful block with multiple injection technique, which was statistically and clinically significant. Mean block performance time in single-injection technique was 117 s (range: 100–120), whereas it was 396 s (range: 360–420) for four injection technique. Thus, the block performance time was significantly higher in multiple injection technique than single-injection method. Mean onset of sensory block in Group 1 and Group 2 was 15.4 min (range: 12–18) and 9.5 min (range: 7–12), respectively. Thus, we noted faster onset of block with multiple injection technique. The onset of motor block was also significantly faster in multiple injection technique. Time for the first analgesic requirement after the surgery was 167 min (range: 120–260) in Group 1 and 201 min (range: 150–270) in Group 2. Duration of analgesia was statistically prolonged in multiple injection group when compared to single-injection group.
Two patients in Group 1 and four patients in Group 2 had accidental arterial puncture during injection while performing the axillary block. Hematoma thus formed was managed by application of pressure and block was performed. This was statistically not significant. None of the patients in either group had any other complications such as local anesthetic toxicity. There was no significant difference in hemodynamic parameters between the groups.
We noted significantly higher success rate for the block when all the four nerves were identified and blocked when compared to injection after identifying a single nerve. This correlates with the other studies which have similarly noted higher block success rate with more number of nerves identified. In our study, the success rate following single injection was 56%, which correlates with the other studies where the success rate have been in the range of 50–57%.[6,7]
With paresthesia technique or transarterial technique, single injection was the norm and traditionally, it was considered that large quantity of local anesthetic deposited around the artery will spread circumferentially and block all the nerves. However, the studies have shown significantly higher failure rates with single-injection technique. Computer tomography studies have attributed the block failure to the presence of septae within the neurovascular sheath, creating a multicompartmental model restricting the circumferential spread of local anesthetics. Other studies also have shown the presence of septae could prevent free diffusion of local anesthetic to all the nerves with the single-injection technique. Furthermore, musculocutaneous nerve lies outside the sheath hence is unlikely to be blocked by single injection. Other studies have suggested blocking musculocutaneous nerve separately along with at least one other nerve to improve the success rate of the block. Lavoie et al. compared single and multiple injections for the axillary block using a nerve stimulator and demonstrated the benefit of considering the musculocutaneous nerve as a separate, preliminary part of any axillary brachial plexus block.
The multiple injection technique for axillary block, in which the main four nerves of the plexus are located by a nerve stimulator and separately injected, has shown to produce a higher success rate of about 90–93% in other studies.[6,7,9] The efficacy in producing a successful block is higher when the individual nerves are targeted even with the small volumes of local anesthetic, rather than large quantity of local anesthetic at a single point. Previous studies have shown that axillary block with double-injection technique using peripheral nerve stimulator provided excellent analgesia and motor block when compared to the single-injection technique. Other studies also have noted that blocking ulnar nerve may not be very essential and blocking median and radial nerves along with musculocutaneous nerve can give success rate >95%.[10,11] In our study, success rate was only 84% even when all the four nerves were blocked. Compared to other studies, we noted higher failure rate in multiple injection group.
Mean block performance time was <2 min in Group 1 and 6.5 min in Group 2. Other studies have noted block performance time of 6–8 min for single injection and about 9–12 min for four injections. The faster block performance in the first group can be explained by the fact that it is easier localize of one of the four nerves compared to trying to localize each of the nerve. The time for block performance was shorter than in other similar studies probably because in our study, the blocks were performed with the help of second person. In addition, we did not consider the time for asepsis and drug preparation as the part of block performance time. Latency of block, which is the time for onset of sensory block, was 15.4 min in the first group and 9.5 min in the second group. This is expected as local anesthetic is closely deposited around nerves in the second group, which fastens the onset of action. In contrast, with the single-injection technique local anesthetic has to spread circumferentially to reach all the nerves and penetrate the various septae present around the nerve; hence, taking much longer time for onset of action. We noted that combined time to perform block and for onset of local anesthetic action was almost same in both the groups, about 17 min. Thus, time saved by the early performance of block in the single-injection group is not much clinically significant as waiting period (latency for the onset of action of block) after the injection is more. Other studies also concur with this finding.
In our study, the average duration of analgesia was 167 min in the single-injection group and 201 min in four injection group. In all probability, local anesthetic is deposited close to the nerve provides longer duration of analgesia than local anesthetic away from the nerve. Although it is common clinical experience that denser block provides longer period of postoperative analgesia, evidence for the same may be lacking. There was no difference in complication rate such as arterial puncture rate between the groups.
The main limitation of the study was that we did not exclude the musculocutaneous nerve stimulation from single nerve injection group. As musculocutaneous nerve lies outside the neurovascular sheath, identification of that might have led to higher failure rate in single-injection group. Hence, the study can be improvised by comparing the blockade of musculocutaneous and one of the other nerve to identification of all the four nerves.
We noted higher success rate, faster onset, longer duration of axillary brachial plexus block when local anesthetic was deposited after identifying four nerves with nerve stimulator, rather than depositing all local anesthetic after identifying only one nerve.
There are no conflicts of interest.