DOI: https://doi.org/10.21203/rs.3.rs-17267/v1
Background. An ultrasound-guided axillary brachial plexus block is usually performed with a multiple-injection technique. However, when the arm is abducted at 160°, the musculocutaneous nerve lies close to the axillary artery, and all four nerves can be blocked with a single-injection. This randomised controlled single-blinded trial tested the hypothesis that a single-injection technique has a reduced procedure time and is as effective as a multiple-injection technique.
Methods. Fifty ASA I-III patients were randomised to receive an ultrasound-guided multiple- or single-injection axillary brachial plexus block with 32ml 1:1 mixture of mepivacaine 1% and ropivacaine 0.5%. In the single injection group, the needle was positioned below the axillary artery, without repositioning, while in the multiple injection group, each nerve was blocked separately. The primary outcome was the procedure time. Secondary outcomes included onset time of action, block success rate 30 minutes after injection, and rest, dynamic pain score (numeric rating scale, 0-10) at 24 postoperative hours.
Results. The procedure time was significantly reduced in the single-injection group with a mean (95%CI) of 6min (5-6), versus 4min (4-4) in the multiple-injection group (p<0.001). Success rates were 96% [95%CI:80%-100%] and 88% [95%CI:69%-97%] in the single- and multiple-injection groups, respectively (p=0.30). Other secondary outcomes were similar between groups, except onset time that was prolonged in the single-injection group with a mean time (95%CI) of 23min (19-27) versus 17min (15-19), p=0.01.
Conclusions. An axillary brachial plexus block performed with a single-injection technique is associated with a reduced procedure time, an increased onset time and an equivalent success rate.
When performing an axillary brachial plexus block under ultrasound-guidance, reducing the number of needle passes decreases needling time, is associated with less paraesthesia, and provides a similar success rate, as demonstrated in a recent systematic review and meta-analysis.1 In that report, all included trials compared a four-injection technique, also called perineural injection, with a two-injection technique or perivascular injection.1 During the four-injection technique employed in the included studies, the radial, ulnar, median and musculocutaneous nerves are blocked with an identical volume of local anaesthetic. In contrast, during the two-injection technique, a higher local anaesthetic volume is administered with the needle tip positioned below the axillary artery, with the goal of spread to the radial, ulnar and median nerves. The musculocutaneous nerve is then blocked with a second injection to account for its location distant from the axillary artery.1
However, the location of this later nerve is dynamic and when patients perform an extreme abduction of the arm, the musculocutaneous nerve comes in close proximity to the axillary artery, due partly to muscle reorganisation.2 This dynamic repositioning offers the potential advantage of blocking four nerves with a single-injection, rather than the previously described two injection-technique.1
We undertook this randomised controlled single-blinded trial to test the hypothesis that a single-injection technique has a shorter procedure time when compared to a multiple-injection technique for ultrasound-guided axillary brachial plexus block.
This study was performed in accordance with the Declaration of Helsinki. It was reviewed and approved by Lausanne University's Institutional Review Board (Commission cantonale d’éthique de la recherche sur l’être humain, protocol number 2017–02185; approval granted April 16, 2018). Written informed consent was obtained from all subjects participating in the trial. The trial was registered prior to patient enrollment at clinicaltrials.gov (NCT03378323, principal investigator: Sina Grape, date of registration December 19, 2017). All patients aged 18 to 85 years who were identified to be American Society of Anaesthesiologists physical status I–III, and who were scheduled to undergo elective forearm or hand surgery between July 2018 and April 2019 at Valais Hospital were eligible to participate in this study. Exclusion criteria included existing neurological deficit in the upper limb, contraindications to peripheral nerve block (e.g., allergy to local anaesthetics, coagulopathy, infection in the area), and pregnancy.
Participating patients were randomly allocated on the day of surgery to either the single- or multiple-injection group, using a computer-generated randomisation table in aggregates of 10. Assignments were concealed in a sealed opaque envelope.
We followed the Consolidated Standards of Reporting Trials (CONSORT) statement’s recommended process.3
All ultrasound-guided blocks were performed prior to surgery, in a dedicated block procedure room and by a single author (SG) who is an experienced regional anaesthesia provider. The patients were positioned supine in a semi-sitting position with their head turned 45 degrees toward the non-operative side. Blood pressure monitoring, pulse oximetry and electrocardiogram were applied to all patients, and supplemental oxygen was administered. After establishing peripheral intravenous (i.v.) access, midazolam 1 to 4 mg i.v. was provided as needed for anxiolysis or sedation. Preparation of the needle insertion site was achieved with chlorhexidine 2% in isopropyl alcohol 70%. Using a sterile technique, a high-frequency linear array transducer (13–6 MHz, SonoSite S-Nerve; SonoSite, Inc, Bothell, Washington) was applied to the site for ultrasound-guidance. For patients assigned to the multiple-injection group, the ipsilateral arm was abducted 90° from the patient’s side, with the elbow bent (Fig. 1). The probe was oriented in a transverse alignment and placed firmly over the axilla, in order to obtain a cross-sectional view of the axillary artery lying superficial to the conjoint tendon, and the radial, ulnar, median and musculocutaneous nerves. Following infiltration of the skin with 1 to 3 ml of lidocaine 1%, a 22-gauge 70-mm insulated block needle (Temena UPC®, Felsberg-Gelsungen, Germany) was inserted from a lateral-to-medial direction, in-plane with the ultrasound beam. As described in the existing literature1, each of the target nerves was blocked separately with 8 ml of local anaesthetic (total volume 32 ml). In the single-injection group, the ipsilateral arm was positioned in extreme abduction from the patient’s side at an angle of 160°, with the elbow bent and the hand under the head (Fig. 1). The ultrasound probe was placed firmly over the axilla, at an angle of approximately 90° to the humerus, in order to image the axillary artery in short view, above the conjoint tendon. An image of the individual nerves was not specifically sought. After local infiltration of the skin, the block needle was inserted in-plane to the ultrasound beam until the tip was positioned below the axillary artery. In this location, a total local anaesthetic volume of 32 ml was injected. In this group, the needle tip was repositioned only if patients complained of paraesthesia.
For both procedures, we ensured that patients did not have access to the ultrasound imaging. All subjects received 32 ml of a 1:1 mixture of mepivacaine 1% and ropivacaine 0.5%, which was slowly injected in 5 ml increments, with intermittent aspiration. Ultrasound visualisation was maintained throughout the procedure. After completion of the block, patients remained fully monitored until their transfer to the operating room.
The assessment of both motor and sensory blockade was performed 5 minutes after local anaesthetic injection by the author (SG) who performed the block and then every 5 minutes thereafter, for a total duration of 30 minutes. The assessment followed a previously published method4 with sensory block evaluated in the dermatomes of the musculocutaneous (lateral side of the forearm), radial (first interdigital space of the dorsum of the hand), median (ventral side of the second finger), and ulnar nerves (ventral side of the fifth finger), using a blunt tip needle pinprick test (0, normal sensation; 1, decreased sensation; 2, no sensation). Motor block was assessed by evaluating elbow flexion (musculocutaneous nerve), thumb abduction (radial nerve), thumb opposition (median nerve) and thumb adduction (ulnar nerve) with the following scale: 0, no loss of force; 1, reduced force compared to contralateral arm; 2 inability to overcome gravity). A successful block was defined as a composite score of 14 or higher within 30 minutes of completing the regional procedure. In the event of a failed block, a supplemental block of the spared nerve at the level of the arm or forearm was performed with 5 mL of the same local anaesthetic mixture, prior to continuing with the surgery.
In the operating room, the same routine monitors were applied and supplemental oxygen was administered. If requested by the patient, conscious sedation was provided via a target-controlled infusion of propofol 0–2 mcg ml− 1. Upon completion of the surgical procedure, patients were transferred to the ward, where a standardized postoperative analgesic regimen consisting of oral acetaminophen 1000 mg every 4 hours (h), and oral ibuprofen 400 mg every eight hours was prescribed. Oxycodone 5 mg every four hours was also made available as needed, which is consistent with our routine practice. Antiemetic treatment with i.v. granisetron 1 mg was made available as needed, as was an i.v. clemastine 2 mg for the treatment of pruritus.
The primary outcome was the block procedure time (defined as the sum of both ultrasound imaging and needling times). Secondary outcomes were either block-related, or pain-related. The block-related secondary outcomes included imaging time (defined as the time interval between probe placement and needle insertion); needling time (defined as the time interval between needle insertion through the skin wheal and the end of local anaesthetic injection); the rate of patient reported paraesthesia; the rate of vascular puncture; pain score during the block procedure (numeric rating scale, NRS, 0–10); time to onset of action (defined as time to reach a composite score of 14 out of 16); block success rate 30 minutes after completion of the block procedure (defined as a composite score of 14 out of 16); duration of the sensory block (defined as time from injection of local anaesthetic to patient perceived recovery of full upper limb sensation); and duration of the motor block (defined as time from injection of local anaesthetic to patient perceived full recovery of arm function). Secondary pain-related outcomes included rest and dynamic pain score (NRS, 0–10) at 24 postoperative hours, time to first opioid request (defined as the time elapsed between block procedure and first oxycodone use), postoperative oxycodone consumption at 24 postoperative hours, and patient satisfaction regarding anaesthetic management (NRS, 0–10, 0 = not satisfied at all, 10 = extremely satisfied).
After completing phase II recovery, patients were discharged home with a diary and were requested to write down the time to recovery of full arm sensation, full arm mobilisation, pain scores at rest and on movement, as well as time of first oxycodone consumption. At 24 postoperative hours, all patients received a phone call by one of the investigators to collect the above-mentioned outcomes, together with questions relating to the presence of hematoma, paraesthesia, or weakness.
Given that the puncture site was identical whether a single- or multiple-injection technique was employed and access to the imaging was not allowed, patients were blinded to the group allocation, as were phase 1 and 2 recovery nurses and the person performing the statistical analysis.
Based on a study by Dr Tran and colleagues, the mean (standard deviation) procedure time was anticipated to be 8.5 (2.3) minutes in the multiple injection group.5 We predicted a 25%-lower procedure time with a single-injection technique. Assuming an alpha error of 0.05 and a power of 90%, we calculated that 18 patients per group were required to detect a statistically significant difference. Allowing for a 30% rate of either protocol violation or drop-out, we planned to recruit a total of 50 patients.
Data were analysed with an intention-to-treat approach. Categorical variables are presented as frequencies and continuous variables are summarised as mean values with 95% confidence intervals (95% CI). Continuous parametric and non-parametric data were compared using the Student’s t test and Mann–Whitney U test, respectively. Categorical and dichotomous data were compared using the Fisher’s exact test or Pearson test as appropriate. Significance was defined at p < 0.05 based on a two-tailed probability. Statistical analysis was performed using the JMP 9 statistical package (SAS Institute, Cary, NC).
Fifty patients were recruited, and all completed the protocol to both measurement of the primary outcome and the follow-up diary. Figure 2 describes the flow of patients during the trial and Table 1 presents the patient characteristics, which were similar between groups.
The procedure time was significantly less in the single-injection group, with a mean (95% CI) of 4 min (4 to 4), versus 6 min (5 to 6) in the multiple-injection group (P < 0.001). Block success rates 30 minutes after the block procedure were 84% [95% CI: 64–95%] and 96% [95% CI: 80–100%] in the single- and multiple-injection groups respectively (P = 0.16). The four patients in the single- and the one patient in the multiple-injection groups with failed blocks all received a supplemental peripheral nerve block and the surgery proceeded uneventfully. In the single-injection failures, the spared nerves included the musculocutaneous nerve twice, the ulnar nerve once and the median nerve once. In the multiple-injection failure, the spared distribution occurred with the radial nerve. Figure 3 presents details of the composite score at each time interval. There were no significant differences between groups at any point in the 30-minute period of block assessment. However, the overall time to onset of action was significantly longer in the single-injection group with a mean of 23 min (19 to 27) versus 17 min (15 to 19) in the multiple-injection group (P = 0.01).
Other block-related outcomes were similar between groups with the exception of needling time, which was significantly reduced in the single-injection group (Table 2). Patients in the multiple-injection group had consumed significantly less oxycodone at 24 postoperative hours, while the other pain-related outcomes were similar between groups (Table 3).
No patient developed complications, such as haematoma, or reported paraesthesia, or weakness in the upper limb during the assessment 24 hours after the procedure.
Based on fifty patients, this single-blinded randomised controlled trial suggests that a single-injection technique for the axillary brachial plexus block requires less needling time, albeit at the expense of a prolonged time to onset of action. While the mean procedure time difference between groups of 2 minutes represents a questionable clinical advantage, it does contribute a small incremental advantage, and although not studied here, the potential advantage could theoretically be of greater impact in the setting of inexperienced providers and trainees. More relevant to the average regional anaesthesia environment are the procedural advantages associated with this technique.
For example, in situations where nerve imaging and identification is difficult, positioning the needle tip just below the axillary artery is typically an easily achievable goal that can ease the technical challenge, while conferring an elevated probability of accurate placement.1 Furthermore, reducing the number of needle passes required to distribute local anaesthetic has been shown to reduce the risk of needle contact with the target nerves,6−8 and therefore may result in less paresthesia or potential for neural injury. Our study was unable to detect an impact on the incidence of nerve injury. However, this is unsurprising as approximately 16,000 patients would be necessary to establish a significant difference between groups for assuming a baseline rate of 0.04% for true nerve injury.9 Given that such a study will likely never be published, we agree with others who have argued that adopting a philosophy of caution when approaching the nerve should be standard and should certainly be considered in a university hospital environment where anaesthetic providers have varying levels of expertise and skills.6,10
The similar block success rate between groups at 30 minutes deserves special consideration. Although our results suggest a trend to favour the multiple-injection group, the absence of statistical significant difference may represent a type II error. A posthoc analysis indicates that a total of 194 patients would be required to detect a difference with this outcome, with alpha and beta values of 0.05 and 0.2. Given the importance of block success, particularly in busy environments where the efficiency gains or losses are most impactful, a trial with success rate as the primary outcome is warranted before reaching a final conclusion regarding the value of the single injection technique. Furthermore, we did not compare the impact on procedure time that was incurred by the need to perform a supplemental nerve block. Any future investigation to explore the impact on block success would benefit from the inclusion of this factor in a robust evaluation of total procedural time.
The observed difference in postoperative opioid consumption identified in this trial should similarly be interpreted with caution given it is a secondary outcome. We feel this is especially warranted as the duration of sensory block and time to first opioid request were similar between groups. This outcome should also be confirmed in a subsequent trial before drawing definitive conclusions. Of note, we elected not to include either intravenous or perineural dexamethasone11,12 or dexmedetomidine13 during this investigation despite the common use of adjuncts in our practice. The impact of injection approach on block onset, duration or analgesic requirements in the setting of adjunct use represents an unknown that may impact the generalizability of our finding to practices where these are common. We suggest this may be a worthwhile question for additional exploration in the setting of the axillary nerve block and the single injection approach.
Given that the block procedure and outcome assessment were performed by a single individual, the study caries the potential bias risks associated with its single-blinded design. However, blinding of the block technique is impossible for the proceduralist and therefore the risk of bias when measuring procedure times is an intrinsic risk with any similar comparative trial. We believe the impact on our secondary results to be negligible, as the patients, caregivers and statistical analysis were masked to group allocation, and a standardised approach was employed to assess outcomes such as block onset and success. In addition, we attempted to limit heterogeneity in our procedures by having all blocks performed by a single operator with established regional anaesthesia expertise. The corollary is that generalisation of these results to a range of technical approaches may be limited. Nonetheless, the potential efficiency gain in block performance from a single-injection technique would likely be greater in operators with less experience. Generalisability may also suffer from challenges with the target patient population. Abduction of the arm to 160° may not be possible for some patients, particularly those with joint issues or range of motion limitations.
In conclusion, an axillary brachial plexus block performed with a sub-arterial single-injection technique is associated with a shorter procedure time, but increased time to onset of action and a limited absolute magnitude of effect. However, the technique permits adoption of a conservative approach to needle-nerve proximity, without a negative impact on procedural time. Several secondary outcomes suggest the need for further investigation including the impact of the technique on block success and on downstream pain outcomes such as opioid consumption.
ASA American Society of Anesthesiologists
CI confidence interval
i.v. intravenous
min inutes
ml milliliters
NRS numeric rating scale
ETHICS APPROVAL AND CONSENT TO PARTICIPATE
This study was reviewed and approved by Lausanne University's Institutional Review Board (Commission cantonale d’éthique de la recherche sur l’être humain, protocol number 2017-02185; approval granted April 16, 2018). Written informed consent was obtained from all participants prior to the trial.
CONSENT FOR PUBLICATION
Written informed consent for publication was obtained from all participants prior to the trial.
AVAILABILITY OF DATA AND MATERIALS
The datasets used and/or analysed for the study are available from the corresponding author on reasonable request.
COMPETING INTERESTS
EA has received grants from the Swiss Academy for Anaesthesia Research (SACAR), Lausanne, Switzerland (50,000 CHF; no grant number attributed), from B. Braun Medical AG (56,100 CHF; no grant number attributed) and from the Swiss National Science Foundation to support his clinical research (353,408 CHF; grant number: 32003B_169974/1). EA has also received an honorarium from B. Braun Medical AG.
No competing interests declared by the other authors.
FUNDING: There was no specific funding for this study.
AUTHORS’ CONTRIBUTIONS
SG: study design, study registration, patient recruitment, block performance, data collection; manuscript editing; KRK: manuscript writing; SB: data interpretation, manuscript editing; EA: study design, statistical analysis, data interpretation, manuscript preparation.
All authors read and approved the manuscript.
ACKNOWLEDGMENTS: None.
1. Albrecht E, Mermoud J, Fournier N, Kern C, Kirkham KR. A systematic review of ultrasound-guided methods for brachial plexus blockade. Anaesthesia 2016; 71: 213-27.
2. Bloc S, Mercadal L, Garnier T, et al. Shoulder position influences the location of the musculocutaneous nerve in the axillary fossa. J Clin Anesth 2016; 33: 250-3.
3. Schulz KF, Altman DG, Moher D. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. PLoS Med. 2010; 7: e1000251.
4. Grape S, Pawa A, Weber E, Albrecht E. Retroclavicular vs supraclavicular brachial plexus block for distal upper limb surgery: a randomised, controlled, single-blinded trial. Br J Anaesth 2019; 122: 518-24.
5. Tran de QH, Russo G, Munoz L, Zaouter C, Finlayson RJ. A prospective, randomized comparison between ultrasound-guided supraclavicular, infraclavicular, and axillary brachial plexus blocks. Reg Anesth Pain Med 2009; 34: 366-71.
6. Albrecht E, Kirkham KR, Taffe P, et al. The maximum effective needle-to-nerve distance for ultrasound-guided interscalene block: an exploratory study. Reg Anesth Pain Med 2014; 39: 56-60.
7. Palhais N, Brull R, Kern C, et al. Extrafascial injection for interscalene brachial plexus block reduces respiratory complications compared with a conventional intrafascial injection: a randomized, controlled, double-blind trial. Br J Anaesth 2016; 116: 531-7.
8. Albrecht E, Bathory I, Fournier N, Jacot-Guillarmod A, Farron A, Brull R. Reduced hemidiaphragmatic paresis with extrafascial compared with conventional intrafascial tip placement for continuous interscalene brachial plexus block: a randomized, controlled, double-blind trial. Br J Anaesth 2017; 118: 586-92.
9. Albrecht E, Kern C, Kirkham KR. A systematic review and meta-analysis of perineural dexamethasone for peripheral nerve blocks. Anaesthesia 2015; 70: 71-83.
10. Albrecht E, Kirkham KR, Taffe P, Brull R. Reply to Drs Bhatt and Hofmann. Reg Anesth Pain Med 2014; 39: 351-2.
11. Baeriswyl M, Kirkham KR, Jacot-Guillarmod A, Albrecht E. Efficacy of perineural vs systemic dexamethasone to prolong analgesia after peripheral nerve block: a systematic review and meta-analysis. Br J Anaesth 2017; 119: 183-91.
12. Kirkham KR, Jacot-Guillarmod A, Albrecht E. Optimal dose of perineural dexamethasone to prolong analgesia after brachial plexus blockade: a systematic review and meta-analysis. Anesth Analg 2018; 126: 270-9.
13. Albrecht E, Vorobeichik L, Jacot-Guillarmod A, Fournier N, Abdallah FW. Dexamethasone is superior to dexmedetomidine as a perineural adjunct for supraclavicular brachial plexus block: systematic review and indirect meta-analysis. Anesth Analg 2019; 128: 543-54.