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  • Supraclavicular Block Vs Interscalene Block for Shoulder Surgeries



    This is the final submission of National University's Binju KC's Scholarly Project. She is a Nurse Anesthesia Resident at National University.

    Does supraclavicular peripheral nerve blockade provide comparable analgesia to interscalene peripheral nerve blockade in patients undergoing shoulder surgeries?


    Binju KC
    National University
    March 9, 2016


    Background

    The shoulder joint is the most flexible joint in the human body; therefore, it is more susceptible to injury than others.1 Surgical interventions may sometimes be performed depending on the nature of the injury. A comprehensive analysis of the epidemiology of shoulder surgeries is beyond the scope of this report. Moreover, the variations in shoulder surgeries based on the type of injury being corrected, the facility setting, and reimbursement model utilized creates numerous obstacles in evaluating their true prevalence. Current evidence suggests that surgical procedures of the shoulder are increasing in frequency.1 When a shoulder injury requires surgical intervention common procedures include arthroscopic debridement, arthroscopic Bankart Procedure (i.e., shoulder stabilization), rotator cuff repair, and shoulder replacement (e.g., hemi-arthroplasty, total shoulder arthroplasty, and reverse total shoulder replacement).2 The reasons for undergoing any of these directly relates to the type of injury sustained. This comprehensive review of current evidence is focused on exploring the dilemmas in choosing between two peripheral nerve blockades of the brachial plexus for shoulder surgeries: interscalene and supraclavicular.

    There are several approaches to providing regional anesthesia for patients undergoing shoulder surgical interventions. Determining the anesthesia management plan is a dynamic process of merging evidence-based practices with patient comorbidities in order to compliment treatment. New evidence emerges in the pursuit of quality, but in so doing requires clinicians to challenge existing evidence with a permissible hypothesis aimed at improving healthcare efficiency. Currently, for surgical procedures of the upper extremities there are a variety of techniques that are utilized for meeting regional anesthesia requirements. The evidence currently establishes the interscalene approach to be the gold standard as a result of numerous studies examining its efficacy in shoulder surgeries; however, insufficient data exists comparing complication rates for interscalene and supraclavicular blocks during frequently performed shoulder surgeries.3,4 This creates a problem for the anesthesia provider since he or she may have limited supporting evidence for the practice of supraclavicular blocks in the setting of shoulder surgery even though it has gained popularity with ultrasound-guidance (USG) due to better visualization of the brachial plexus.5 As such, it is pertinent to ask the following: Does supraclavicular peripheral nerve blockade provide comparable analgesia to interscalene peripheral nerve blockade in patients undergoing shoulder surgeries? This report shall attempt to answer that question.
    Significance

    In order to evaluate the significance of the aforementioned anesthesia interventions, we must first explore the characteristics of the anesthetic methods possible to use for such a surgery. Much like a tool in a toolbox, the degree of usefulness of an anesthetic technique is directly associated to the situation for which it is used and how it is used. General anesthesia (GA) is the act of administering volatile anesthetic gases via controlled inhalation to medically induce a coma preventing autonomic nervous system reflexes, consciousness, and recollection. This differs from regional anesthesia (i.e., local anesthesia) in that regional anesthesia seeks to prevent sensation to a given region of the body. When compared to GA, regional may lead to a reduction in systemic analgesia requirements, opioid side effects, stress response, and incidence of chronic pain.6

    Because of the focused nature of local anesthesia, there exist multiple locations that are targeted depending on the surgical procedure to be performed. Regional anesthesia for shoulder surgeries is classically achieved by performing a peripheral nerve block to the brachial plexus by an interscalene approach, (i.e., an interscalene block).3 This is due to anatomical considerations; the roots of C5 through C7 are densely blocked with such an approach.6 By comparison, an increase in frequency for a blockade of the brachial plexus via a supraclavicular approach (i.e., a supraclavicular block) has been more recently observed.5, 7 The reason is due to a number of factors, including – most predominantly – the increased utilization of ultrasound guidance.8 A supraclavicular block densely anesthetizes the brachial plexus. Typically such an approach was reserved for procedures at or distal to the elbow.6
    There are a number of elements that contribute to the success or failure of each blockade.
    Starting with the patient, those who have suffered previous injury to the targeted nerves or who have a relevant pre-existing condition (e.g., peripheral neuropathy) might carry a greater chance of a prolonged sensory motor block.6 In some cases it may even become permanent.6 However, a greater influence to the success or failure of either blockade can be attributed to the way in which it is administered. Performing a nerve-stimulated technique can be facilitated with the aid of electrical current -- usually in the range of 0.2 to 0.5 milliamps (mA) -- in order to induce muscle response for the targeted nerve.6 This technique offers more accuracy and precision than the older paresthesia technique – leading to paresthesia technique becoming largely abandoned.6 Enhancing accuracy and precision further, there has been increasing popularity in the use of ultrasound-guidance. This technique allows visualization of the nerve bodies and needle. Using this method, the practitioner usually administers less anesthetic agents compared to nerve-stimulated blocks.6

    This decrease in anesthetic agent use and time to achieve anesthesia are substantial factors in increasing the efficiency of anesthesia services. The reason is because doing so has both physiological and economic benefits.6,9 The patient receives less local anesthetic (LA) via ultrasound-guided (10-30 mL) versus nerve-stimulated (30-40 mL) technique which may help reduce potential toxicity in instances where anesthetic agents are injected intravascularly or on occurrence of vascular puncture.6, 4 It is also the case that patients receiving peripheral nerve blocks instead of traditional intravenous opioids and NSAIDS demonstrate less morbidity and mortality.10

    Current evidence has demonstrated that as much as 68% of patients undergoing shoulder surgeries may bypass the recovery room altogether when regional anesthesia is used exclusively.11 This was found to be the case when comparing an interscalene block (ISB) to both a combination of interscalene block with general anesthesia and general anesthesia alone.11 In those situations, when the ISB patients do go to the recovery room, they have the shortest stays there, are the first to ambulate, intake food, and the last to experience a recurrence of pain.11 In addition, operating costs saved to surgical facilities have been estimated to be $97,000 a year due to decreases in time to onset of satisfactory surgical conditions.9

    As reimbursement for services becomes more integrated with -- and dependent on -- patient satisfaction, optimal pain management will be increasingly essential. These savings to the facility can extend beyond the surgical suite and patients’ recovery has been noted to decrease when using less analgesic adjuvants and more target-specific anesthetic methods.

    Summary of Evidence

    Comparing interscalene (ISB) and supraclavicular (SCB) nerve blocks in shoulder surgeries have been a recent development because of the former infrequency and high risk of complications that SCBs entailed. Due to the advancement of USG, increasing amounts of data can potentially be used for comparing SCB and ISB in shoulder surgery settings.5 In 2011, Conrad and Awad concluded that SCB showed “undoubted effectiveness” in shoulder surgeries.12 What follows is a continued examination of current evidence for ISB and SCB. A comprehensive review of the literature was performed to contrast and compare the effectiveness of ISB and SCB alone in shoulder surgery.

    In 2010, Coşkun et al.13 investigated characteristics of sensory and motor blocks to the brachial plexus via axillary, supraclavicular, and interscalene approaches on 75 patients undergoing upper extremity orthopedic surgery. Though the blocks were not performed with USG, they examined onset, quality, and extent of blockade from both ISB and SCB. The researchers divided the total number of patients into three equal groups composed of 25 individuals – AX for axillary, SC for supraclavicular, and IS for interscalene. All patients received brachial plexus blocks with approaches correlating to their designated group.

    Monitoring each patient at set intervals, assessments of sensory and motor blockade were performed. Three nerves served as inputs for these assessments: medial antebrachial cutaneous, medial brachial cutaneous, and intercostobrachial. There were statistically different results among the various approaches with supraclavicular obtaining the greatest average percentage of nerves blocked. The researchers then cross-referenced their findings with other studies and determined that their results were similar. The authors conclude, however, that variations in location of surgical interventions are vital in determining how the complex brachial plexus – and potentially the cervical plexus – is approached and blocked. They suggest that knowledge of all approaches are useful in determining the most suitable anesthetic plan. Such research adds to the question of whether USG may offer alternative regional anesthesia such as SCB viability for shoulder surgeries.

    A prospective study by Singh et al.14 sought to examine the patient satisfaction, efficacy, and safety of USG ISB on 1319 patients undergoing arthroscopic shoulder surgery. Experienced anesthetists administered USG ISBs at an outpatient shoulder surgical center and physicians assessed satisfaction as well as any adverse events 24-hours postoperatively. If positive for adverse events, individuals were followed until the symptoms were resolved.

    The authors found the interscalene blocks to be 99.6% successful while noting a 2.88% incidence of adverse events. At the last follow-up before publishing, the authors admitted to three patients (0.23%) who had permanent sequelae but noted that they had relevant comorbidities as well – distorting relevant conclusions from their misfortune. The authors support further use of interscalene blocks for pre-screened patients electing to have shoulder arthroscopy performed. This data is constrained to USG ISB alone for surgical interventions of the shoulder; however, results such as these could contribute to potential meta-analysis for USG ISB.

    Research conducted by Perlas, et al.15 from the University of Toronto’s Department of Anesthesia and Toronto Western Hospital’s Department of Anesthesia and Pain Management examined the success rates of SCB to the brachial plexus via USG. Most of the patient data reviewed was from outpatient surgical interventions (460), but inpatient outcomes (50) were observed as well. Also captured in the review was the factor of technical experience in that 47 different practitioners at various levels of training performed the SCBs. They found that the SCBs yielded a 94.6% success rate in brachial plexus blockade for surgical anesthesia on a single attempt. Complications such as symptomatic hemidiaphragmatic paresis, Horner syndrome, unintended vascular punctures, and transient sensory deficits were statistically rare at 1%,1%,0.4%, and 0.4% respectively for a total complication percentage of 2.80%. USG ISBs conducted by Singh et al. came with a total complication rate of 2.88% which included transient neurological events such as ear (n=14) and digital (n=8) numbness, distal ulnar mononeuropathy (n=1), and postoperative brachial plexitis (n=3), two of which did not resolve.

    It is worth noting that Perlas et al. was a review of outcome data from patients who had received such anesthesia for surgeries of the upper extremity. Establishing blockade of the brachial plexus can vary depending on the region exposed to surgical stimulation. Nonetheless, it demonstrated safety for SCB, citing only coagulopathy and severe underlying respiratory disease as contraindications for such procedures.

    The volume of LA required to achieve appropriate brachial plexus blockade via SCB has also recently been examined. Duggan et al.16 sought to determine the minimum effective anesthetic volume (MEAV) needed for a successful SCB placed under USG in 21 patients. They used a testing methodology known as the Dixon and Massey up-and-down – a process whereby a dose is determined for a patient based on the success or failure of the previous patient’s volume received. For example, if a patient received an initial dose of 30 mL that provided inadequate anesthesia, the subsequent patient would receive an initial dose of 35 mL. Conversely, if a patient received an initial dose of 30 mL that provided adequate anesthesia, the subsequent patient would receive an initial dose of 25 mL.

    Using this method, the researchers found the MEAV for 50% of patients to be 23 mL and 42 mL for 95% of patients. They concluded that these amounts do not statistically differ from other conventional, non-USG techniques of SCB such as nerve-localization. Again, this research was conducted only on patients that were undergoing surgical procedures of the upper extremity that excluded interventions to the shoulder. However, because SCBs of the brachial plexus are considered to be ideal for upper extremity surgeries, it is valuable in scrutinizing its classical characteristics as we begin to examine its more nuanced use in shoulder surgeries.

    Šaric´ et al.17 extended this perspective to observe the effects of aging on MEAV from SCBs in a study roughly twice as large. The up-down methodology used in the aforementioned study was applied here as well. They employed their prospective, observer-blinded study in a population of patients middle-aged (>25< 50, n=22) to elderly (>65, n=22).

    They concluded that the MEAV for 50% of the population (MEAV50) did indeed vary depending on the age of the patient. Middle-aged adults required an average of 23.0 mL and the elderly group only required 11.9 mL on average. Some limitations the authors disclose is that the MEAV50 does not accurately predict outcomes when extrapolated to 95% of the population. Also, the nerve boundaries captured on the ultrasound can be subject to the operator’s skill at identifying them. It was noted that elderly patients had a smaller surface area of a brachial plexus, potentially affecting the dose required.

    Muhly et al.18 examined the frequency with which small vessels branching from the subclavian veins and arteries are found to be interconnected to or a close proximity from the brachial plexus that could alter effectiveness of either interscalene or supraclavicular blocks. Using ultrasound, the authors documented the presence of such vessels in 50 selected patients who would be undergoing shoulder arthroscopies.

    The results were that in supraclavicular regions an artery was either passing adjacent to or directly through the brachial plexus in 86% of the patients. In interscalene regions an artery was passing in a lateral direction of the brachial plexus in 90% of the patients while a smaller vein was found medial-to-lateral in this region in 46% of the subjects. In addition to this, the authors correlated their findings with three non-preserved cadavers that they dissected in order to evaluate the anatomy and cross-reference their scanned findings. Cautionary results such as these are meant to aid the anesthetist in his or her decision-making when considering a brachial plexus block.

    Perhaps one of the most extensive studies to date that examines USG SCB efficacy in the setting of shoulder surgeries is from Liu et al.4 A prospective clinical registry was developed and explored. The researchers used a relatively large sample size of 1,169 patients who received either an ISB (n=515) or SCB (n=645) under USG for ambulatory shoulder arthroscopies coupled with neurological prescreening and a blinded follow-up that assessed post-operative neurological symptoms (PONS). It illustrated differences in success rates and rates of complications between supraclavicular and interscalene blocks. Their study distinguished itself from two commonly explored registry types: those that compared various USG non-ISB regional anesthesia interventions and those that focused on stimulator-guided blocks such as Coşkun et al.

    The methods for the study were well-documented; selection criteria were designed and followed, consent was signed, basic neurological conditions evaluated, surgical plans screened, blocks properly executed, and post-surgical assessments that followed a week later utilized the same assessment mechanisms. It also followed participants until resolution of postoperative neurological symptoms and then statistically analyzed the data – ultimately concluding that supraclavicular blocks under ultrasound-guidance were a safe and effective alternative to interscalene blocks. There were no clinical signs of pneumothorax for any patient in the SCB group, which echoes Perlas et al. findings. It is especially helpful to this review in that it truncated the data to ambulatory shoulder arthroscopies with SCBs placed via USG.

    Several factors were illuminated in Liu et al. regarding the efficacy of either anesthetic intervention. 61 percent of both ISB and SCB blocks were done by attending anesthesiologists. The remainder (39%) were completed by residents or fellows under supervision. There were absolutely no vascular punctures for either ISB or SCB groups. However, 0.3% of SCBs were classified as a block failure requiring GA. Intravenous opioid use for rescue postoperative pain control was 0.6% for both ISB and SCB. Observed hoarseness in the PACU was the most prevalent side effect observed for both ISB and SCB; however, the incidence was higher for ISB (31%) versus SCB (22%). Both groups shared a duration of 2 days for this side effect, but those who received an ISB subjectively reported hoarseness at a greater rate (11%) than SCB (6%) during the first week after the procedure. Dyspnea was more common in the ISB group (10%) compared to the SCB group (7%) as well as PONS (0.6%) on follow-up one week later. The PONS did eventually resolve in all ISB cases by 3 months post-op. There was no incidence of PONS for the SCB group on follow-up. Both ISB and SCB used similar amounts of LA (49 mL and 51 mL respectively). Of great significance was the patient satisfaction scores between both ISB and SCB groups: a tied score of 8 out of 10 with 10 being the most satisfied.
    Ryu et al.19 is the most recent study to examine the efficacy surrounding USG ISB and SCB for shoulder arthroscopies. Sensory and motor blockade, incidence of side effects, and opioid requirements during the intraoperative period were examined. Of special interest to the authors was the amount of local anesthetic needed for such interventions as the results observed in Liu et al. for either ISB or SCB were in similar quantities to those often seen when USG is not used.

    Subjects were assigned at random to either receive an USG ISB (n=47) or an USG SCB (n=46). Motor and sensory blockade was assessed by a blinded anesthesiologist. For sensory blockade assessment, the anesthesiologist touched an alcohol swab to the dermatomes of the shoulder and the patient then scored its sensation between 0 (loss of cold sensation) and 100 (intact sensation) 20 minutes after receiving the LA (25 mL). Evaluation of the motor blockade was conducted by rating forces of muscle contractions between four nerves: radial, ulnar, median, and musculocutaneous. The rating scale was 0 (complete paralysis) to 6 (normal muscle force).

    Though the size of this study was smaller than that of Liu et al., significant data was found with which to draw some conclusions. Of great importance was that no patients received GA due to inadequate regional anesthesia even though the ISB group obtained significantly better sensory blockade than the SCB group (i.e., lower average sensory scores). However, the SCB group obtained significantly better motor blockade of the radial, medial, and ulnar nerves (i.e., lower average motor scores). Side effects such as Horner’s syndrome and hoarseness were more common among ISB subjects (28;5) than SCB (9;2). Patients requiring intraoperative opioid use (i.e., subsequent fentanyl injections) were “comparable” between ISB (13) and SCB (14) groups. With these results, the authors also concluded that USG SCB seems to be an adequate alternative to USG ISB for shoulder surgeries.

    Recommendations for Practice

    The objective in using USG SCBs for shoulder surgeries is to provide potentially favorable alternatives to ISBs when circumstances warrant its use. This, of course, means appropriately surveying patient’s comorbidities and concurrent medication regimens. The American Society of Regional Anesthesia and Pain Medicine (ASRA), for instance, recommends a 7-day cessation of clopridogrel for patients undergoing regional anesthesia.20 There is ongoing research being conducted to examine what benefits or disadvantages can be consistently realized for SCBs. In addition, the research that focuses on directly comparing shoulder surgery USG SCBs to ISBs is in its infancy. It is here that we might form recommendations pertinent to settings that may necessitate choosing between these blocks.
    Considerations surrounding the use of SCBs or ISBs under USG are multifaceted and more fundamentally linked to the physical logistics of injecting local anesthetic near nervous tissue. As mentioned by Liu et al. and the ASRA, a very low-occurrence complication that can still present itself is the unintended intraneural trauma and injection which can lead to PONS.21 It is continually debated that intraneural injection can occur and not yield any PONS, however.22 Additional recommendations further stem from the general practice guidelines consistent with any regional anesthetic. Potential vascular complications associated with the risk of injecting anesthetic into the brachial plexus are not easily obtainable in live human trials. This makes research such as that conducted by Muhly et al. indicative in determining which approach carries the least risk.

    Perhaps the greatest reason for contemplating USG SCBs for shoulder surgeries to begin with is due to variations in patient anatomy that rewards a supraclavicular orientation rather than interscalene. This was noted in Liu et al. where they observed better visualization of the brachial plexus in the supraclavicular fossa.4 They also cited revelations that SCBs have been shown via ultrasound and computed tomography scanning that LA travels cephalad between medial and anterior scalene muscles – thereby rebutting previous concerns that the SCBs are too distal from cervical nerve roots to be effective in shoulder surgeries.4 The patient satisfaction scores cited by Singh et al. for subjects who received the SCB help validate such observations; therefore, this author would recommend using USG SCB for shoulder surgeries when adequate ultrasound equipment is available and when there is a better view of the brachial plexus in the supraclavicular fossa. Since, according to the New York School of Regional Anesthesia (NYSORA), the number of attempts and volume of LA used for the interventions depends on the adequacy the observed spread of the LA.23

    Conclusion

    Best practices are arrived at after an objective, empirically-sought pursuit of scientific evidence in order to answer clinically relevant questions. As technology and its implementation changes and evolves, clinicians serve their constituents well by reassessing the effects of those changes. In this context, there appears to be some evidence in the research so far that may support the anesthesia provider’s increased use of USG SCBs in shoulder surgeries. However, factors such as patient characteristics, location of surgical interventions, and technological constraints continue to take priority in determining what regional approach to use for shoulder surgeries.

    Current research suggests, as does this author, that USG SCBs are favorable alternatives to USG ISBs in the setting of shoulder surgeries. Results between various studies may need further research in order to articulate original findings. This is perhaps best illustrated when Ryu et al. sought to better determine the amount of LA needed to achieve a sufficient blockade after seeing the amounts published in the findings of Liu et al. Similarly, when Šaric´ et al. sought to expand the results Duggan et al. published regarding the MEAV required for USG SCBs they contributed valuable evidence surrounding SCB’s use in shoulder surgeries. However, more large-scale research is needed to properly establish USG SCBs as better alternatives to USG ISB for surgeries of the shoulder.

    References

    1. Kim SH, Wise BL, Zhang Y, Szabo RM. Increasing incidence of shoulder arthroplasty in the United States. J Bone Joint Surg Am. 2011;93(24):2249-54. doi: 10.2106/JBJS.J.01994.

    2. Shoulder injuries and disorders. National Institutes of Health U.S. National Library of Medicine Medline Plus Web Site. https://www.nlm.nih.gov/medlineplus/shoulderinjuriesanddisorders.html. Published July 24, 2014. Updated August 4, 2015. Accessed August 14, 2015.

    3. Bowens C, Sripada R. Regional blockade of the shoulder: approaches and outcomes. Anesthesiol Res Pract. 2012;2012:971963.

    4. Liu SS, Gordon MA, Shaw PM, Wilfred S, Shetty T, Yadeau JT. A prospective clinical registry of ultrasound-guided regional anesthesia for ambulatory shoulder surgery. Anesth Analg. 2010;111(3):617-23.

    5. Hanumanthaiah D, Vaidiyanathan S, Garstka M, Szucs S, Iohom G. Ultrasound guided supraclavicular block. Med Ultrason. 2013;15(3):324-9. doi: 10.11152/mu.2013.2066.153.dh1mg2

    6. Butterworth J, Mackey DC, Wasnick J in Morgan and Mikhail's Clinical Anesthesiology, 5th edition. McGraw Hill Professional; 2013: 975-1022.

    7. Hagen K, Iohom G. Pain management for ambulatory surgery: what is new. Curr Anesthiol Rep. 2014;4:326-33. doi: 10.1007/s40140-014-0079-0

    8. Koyyalamudi VB, Arulkumar S, Yost BR, Fox CJ, Urman RD, Kaye AD. Supraclavicular and paravertebral blocks: Are we underutilizing these regional techniques in perioperative analgesia?. Best Pract Res Clin Anaesthesiol. 2014;28(2):127-38.

    9. Thomas LC, Graham SK, Osteen KD, Porter HS, Nossaman BD. Comparison of ultrasound and nerve stimulation techniques for interscalene brachial plexus block for shoulder surgery in a residency training environment: a randomized, controlled, observer-blinded trial. Ochsner J. 2011;11(3):246-52.

    10. Cho CH, Song KS, Min BW, Jung GH, Lee YK, Shin HK. Efficacy of interscalene block combined with multimodal pain control for postoperative analgesia after rotator cuff repair. Knee Surg Sports Traumatol Arthrosc. 2015;23(2):542-7. doi: 10.1007/s00167-012-2272-3.

    11. Lehmann LJ, Loosen G, Weiss C, Schmittner MD. Interscalene plexus block versus general anaesthesia for shoulder surgery: a randomized controlled study. Eur J Orthop Surg Traumatol. 2015;25(2):255-61. doi: 10.1007/s00590-014-1483-3.

    12. Conroy PH, Awad IT. Ultrasound-guided blocks for shoulder surgery. Curr Opin Anaesthesiol. 2011;24(6):638-43.

    13. Coşkun D & Malhi A. The extent of blockade following axillary, supraclavicular, and interscalene approaches of brachial plexus block. Turk J Med Sci. 2011; 41(4):623-31. doi: 10.3906/sag-1008-1091

    14. Singh A, Kelly C, O'brien T, Wilson J, Warner JJ. Ultrasound-guided interscalene block anesthesia for shoulder arthroscopy: a prospective study of 1319 patients. J Bone Joint Surg Am. 2012;94(22):2040-6. doi: 10.2106/JBJS.K.01418

    15. Perlas A, Lobo G, Lo N, Brull R, Chan VW, Karkhanis R. Ultrasound-guided supraclavicular block: outcome of 510 consecutive cases. Reg Anesth Pain Med. 2009;34(2):171-6.

    16. Duggan E, El beheiry H, Perlas A, et al. Minimum effective volume of local anesthetic for ultrasound-guided supraclavicular brachial plexus block. Reg Anesth Pain Med. 2009;34(3):215-8.

    17. Šarić JP, Vidjak V, Tomulić K, Zenko, J. Effects of age on minimum effective volume of local anesthetic for ultrasound-guided supraclavicular brachial plexus block. Acta Anaesthesiol Scand. 2013; 57(6):761-66. doi: 10.1111/aas.12109

    18. Muhly WT, Orebaugh SL. Sonoanatomy of the vasculature at the supraclavicular and interscalene regions relevant for brachial plexus block. Acta Anaesthesiol Scand. 2011;55(10):1247-53. doi: 10.1111/j.1399-6576.2011.02528.x

    19. Ryu T, Kil BT, Kim JH. Comparison Between Ultrasound-Guided Supraclavicular and Interscalene Brachial Plexus Blocks in Patients Undergoing Arthroscopic Shoulder Surgery: A Prospective, Randomized, Parallel Study. Medicine (Baltimore). 2015;94(40):e1726.

    20. Narouze S, Benzon HT, Provenzano DA, et al. Interventional spine and pain procedures in patients on antiplatelet and anticoagulant medications: guidelines from the American Society of Regional Anesthesia and Pain Medicine, the European Society of Regional Anaesthesia and Pain Therapy, the American Academy of Pain Medicine, the International Neuromodulation Society, the North American Neuromodulation Society, and the World Institute of Pain. Reg Anesth Pain Med. 2015;40(3):182-212.

    21. Neal JM, Bernards CM, Hadzic A, et al. ASRA Practice Advisory on Neurologic Complications in Regional Anesthesia and Pain Medicine. Reg Anesth Pain Med. 2008;33(5):404-15.

    22. Bigeleisen PE, Moayeri N, Groen GJ. Extraneural versus intraneural stimulation thresholds during ultrasound-guided supraclavicular block. Anesthesiology. 2009;110(6):1235-43.

    23. Ultrasound-Guided Interscalene Brachial Plexus Block. New York School of Regional Anesthesia. Available at: http://www.nysora.com/techniques/ult...xus-block.html. 2013; Accessed March 9, 2016.
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