Can J Anesth/J Can Anesth DOI 10.1007/s12630-014-0237-3
CASE REPORTS / CASE SERIES
Refining the ultrasound-guided interscalene brachial plexus block: the superior trunk approach Raffinement du bloc interscale´nique e´choguide´ du plexus brachial: la voie de la branche supe´rieure David Burckett-St.Laurent, MBBS • Vincent Chan, MD • Ki Jinn Chin, MBBS Received: 14 May 2014 / Accepted: 3 September 2014 Ó Canadian Anesthesiologists’ Society 2014
Abstract Purpose The conventional ultrasound-guided interscalene block targets the C5 and C6 nerve roots at approximately the level of the cricoid cartilage where they lie in the groove between the anterior and middle scalene muscles. This technique, although effective at providing regional anesthesia of the shoulder, is associated with risks of phrenic nerve palsy, injury to the dorsal scapular and long thoracic nerves, and long-term postoperative neurologic symptoms. In this case report, we describe the ultrasoundguided superior trunk block. This procedure targets the C5 and C6 components of the brachial plexus more distally after they unite into the superior trunk but before the suprascapular nerve branches off. Clinical features We performed an ultrasound-guided superior trunk block to provide perioperative analgesia for ambulatory arthroscopic shoulder repair in a patient with moderate chronic obstructive pulmonary disease. The technique, relevant sonoanatomy of the brachial plexus, and the potential advantages of the superior trunk block are discussed.
Electronic supplementary material The online version of this article (doi:10.1007/s12630-014-0237-3) contains supplementary material, which is available to authorized users. Author contributions David Burckett-St.Laurent and Ki Jinn Chin contributed substantially to the conception and drafting of the article. David Burckett-St.Laurent, Vincent Chan, and Ki Jinn Chin contributed substantially to the design and drafting of the article. D. Burckett-St.Laurent, MBBS V. Chan, MD K. J. Chin, MBBS (&) Department of Anesthesia, Toronto Western Hospital, University of Toronto, 399 Bathurst St., Toronto, ON M5T 2S8, Canada e-mail: [email protected]
Conclusion The enhanced anatomical knowledge provided by ultrasound-guidance has allowed anesthesiologists to devise new block techniques and refine existing ones. The superior trunk block is an example of this refinement and is intended as an alternative to the conventional interscalene block for anesthesia of the shoulder. Further research is planned to confirm the efficacy and safety of the technique. Re´sume´ Objectif Le bloc interscale´nique e´choguide´ conventionnel cible les racines nerveuses C5 et C6 approximativement a` la hauteur du cartilage cricoı¨de ou` elles traversent un espace entre les muscles scale`nes ante´rieur et moyen. Bien que cette technique produise une anesthe´sie re´gionale efficace de l’e´paule, elle est associe´e a` des risques de paralysie du nerf phre´nique, de le´sion du nerf dorsal de la scapula et des nerfs thoraciques longs, ainsi qu’a` des ˆ mes neurologiques postope´ratoires a` long terme. sympto Dans ce rapport de cas, nous de´crivons un bloc e´choguide´ de la branche supe´rieure. Cette proce´dure cible les branches C5 et C6 du plexus brachial plus distalement, apre`s leur union pour former la branche supe´rieure, mais avant la division du nerf suprascapulaire. Caracte´ristiques cliniques Nous avons pratique´ un bloc e´choguide´ de la branche supe´rieure pour obtenir une analge´sie pe´riope´ratoire au cours d’une re´paration de l’e´paule par voie arthroscopique en ambulatoire chez un patient ayant une maladie pulmonaire obstructive chronique d’intensite´ mode´re´e. La technique, l’anatomie e´chographique pertinente du plexus brachial et les avantages du bloc de la branche supe´rieure sont discute´s. Conclusion L’ame´lioration des connaissances anatomiques procure´e par l’e´choguidage a permis aux anesthe´siologistes de mettre au point de nouvelles techniques de blocs et de
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raffiner celles qui existent. Le bloc de la branche supe´rieure est un exemple de ce raffinement et est vu comme une technique de remplacement du bloc interscale´nique conventionnel pour l’anesthe´sie de l’e´paule. D’autres e´tudes sont pre´vues pour confirmer l’efficacite´ et l’innocuite´ de la technique.
The interscalene block is a valuable analgesic option in shoulder surgery. It targets the C5 and C6 roots of the brachial plexus that give rise to the suprascapular nerve, axillary nerve, and lateral pectoral nerves that innervate the shoulder joint. The most common technique of ultrasoundguided interscalene block involves imaging the C5 and C6 roots at approximately the level of the cricoid cartilage, just distal to where they emerge from behind their respective transverse processes and where they lie in the groove between the anterior and middle scalene muscles (Fig. 1). The block needle is usually advanced in plane in a lateralto-medial direction through the middle scalene muscle to contact the nerve roots and inject local anesthetic around them.1 Although this is a highly effective technique, it has some limitations, including a reported incidence of three cases per 1,000 of long-term (more than six months) postoperative neurologic symptoms (most commonly paresthesia or numbness; very rarely motor weakness)2 and an ever-present risk of phrenic nerve palsy despite injection of volumes as low as 5 mL.3,4 In this case report, we describe an alternative approach to C5/C6 blockade the ultrasound-guided superior trunk block.
Case illustration Written informed consent was obtained from the patient for inclusion in this report. A 55-yr-old male was scheduled for right arthroscopic shoulder surgery (Bankart repair with remplissage procedure) as an ambulatory surgery case. He was a heavy smoker with an 80-pack-year history and daily recreational use of marijuana, with resulting moderate chronic obstructive airways disease. Pulmonary function tests revealed post-bronchodilator values of FEV1/FVC 52% and FEV1% 62%. His medications included inhaled bronchodilator therapy (budesonide, formoterol, tiotropium bromide) and a statin for hypercholesterolemia. After discussing risks and benefits, the patient agreed to receive an ultrasound-guided superior trunk block for postoperative analgesia. After applying standard monitoring,5 an ultrasoundguided superior trunk block was performed using a linear
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Fig. 1 Dissection of the right brachial plexus above the clavicle. The conventional ultrasound-guided interscalene block targets C5 and C6 roots in the interscalene groove between the middle scalene muscle (MSM) and the anterior scalene muscle (ASM), just distal to where they emerge from under the sternocleidomastoid muscle (SCM). More distally, the C5 and C6 roots rise out of the groove and unite to form the superior trunk. The probe image and the dotted rectangle indicate the probe locations for the conventional interscalene block and superior trunk block, respectively. Observe the phrenic nerve (black arrows) descending in a medial direction over the ASM away from the brachial plexus as well as the artery crossing the C7 and C8 roots. (Image adapted with permission from D. Jankovic and reproduced with permission from www.usra.ca)
high-frequency (5-12 MHz) probe and a 22G 50-mm StimuplexÒ block needle (B. Braun, Mississauga, ON, Canada). An injection of 0.25% bupivacaine 12 mL with epinephrine 0.0025 mgmL-1 was administered, and an additional 5 mL of local anesthetic was injected superficial to the middle scalene muscle to block the supraclavicular nerves (lower branches of the superficial cervical plexus supplying the ‘‘cape’’ area of the shoulder).6 The patient exhibited motor and sensory blockade at 15 min without any subjective increase in work of breathing. Ultrasound of the ipsilateral diaphragm did not show paradoxical movement, further supporting an absence of clinically significant phrenic nerve paralysis. The patient subsequently underwent a successful surgical repair under general anesthesia. His recovery was rapid and uneventful, and he was discharged four hours after emergence from anesthesia. At telephone follow-up the next day, the patient reported excellent postoperative analgesia with onset of pain evident approximately 23 hr after block completion. This was
The superior trunk brachial plexus block b Fig. 2 A sequential series of images of the brachial plexus above the
clavicle from proximal to distal. (A) A transverse oblique view of the C5 (smaller hypoechoic circle) and C6 (larger circle) in the most proximal part of the interscalene groove, just under the lateral border of the sternocleidomastoid muscle (SCM). (B) The C6 root has split in characteristic fashion into two separate hypoechoic circles. The phrenic nerve (arrow) is visible in this individual on the surface of the anterior scalene muscle (ASM). (C) The C7 root has entered the interscalene groove, lying deep to C5 and C6. (D) The C5 and C6 roots have coalesced into the superior trunk, which has a well-defined hyperechoic boundary. The block needle is advanced in plane under the deep cervical fascia overlying the middle scalene muscle (MSM) until its tip is adjacent to the lateral aspect of the superior trunk. Injection here should produce spread around, but not within, the superior trunk. (Image courtesy of www.usra.ca)
transverse process (Fig. 2A) and entering the groove between the anterior and middle scalene muscles (Fig. 2B and 2C). It is noteworthy that, in up to 30-35% of individuals, the C5 nerve root takes an anomalous course over or through the anterior scalene muscle rather than the interscalene groove (Fig. 3).7,8 Ultrasonographic identification of this anomaly is complicated by the fact that the C6 nerve root almost always splits into two hypoechoic bundles within the interscalene groove and can thus be mistaken for two separate roots (Fig. 2B and 2C; Fig. 3).8 It is vital to recognize this normal splitting of C6, as injection between these two structures would constitute an intraneural injection. The C5 and C6 roots become increasingly superficial within the interscalene groove and eventually unite to form the superior trunk (Fig. 1), which is visible as a single complex structure with a hyperechoic connective tissue boundary lying just below the prevertebral (deep cervical) fascia (Fig. 2D). More distally in the root of the neck, the C8 and T1 roots unite to form the inferior trunk, while the C7 root forms the middle trunk.9 The trunks bifurcate into anterior and posterior divisions posterior to the clavicle,10 and these comprise the complex ‘‘bunch of grapes’’ appearance of the brachial plexus as it crosses the first rib in the ultrasonographic view that is used in the supraclavicular block.
Technical description of the superior trunk block
adequately controlled with oral analgesics. He had no respiratory or neurological symptoms.
Review of anatomy and sonoanatomy The C5 and C6 roots are visible on ultrasound as dark hypoechoic circles emerging from their respective
The C5 and C6 nerve roots are identified within the interscalene groove, but instead of targeting them at this level, they are traced distally to where they coalesce into the superior trunk. The block needle is advanced in plane in a lateral-to-medial direction under the deep cervical fascia and superficial to the middle scalene muscle until the tip is just adjacent to the lateral boundary of the superior trunk (Fig. 2D). An out-of-plane approach may also be used if preferred. Injection of local anesthetic at this point will
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Fig. 3 An example of an anomalous course of the C5 root, which, in this case, travels through and then superficial to the anterior scalene muscle (ASM), remaining outside the interscalene groove. As the brachial plexus is followed more distally, C5 will be seen to unite eventually with C6 to form the superior trunk. Observe that both the C6 and C7 roots in this individual have a ‘‘double bundle’’ appearance. (Image courtesy of www.usra.ca)
hydrodissect the tissue plane around the superior trunk, and 10-15 mL will spread around it with minimal need for needle repositioning (see Video; available as Electronic Supplemental Material). It is crucial to target the superior trunk proximal to the takeoff of the suprascapular nerve. This nerve is identified as a small hypoechoic circle that separates from the lateral aspect of the superior trunk (Figure 4) and courses laterally under the omohyoid muscle away from the brachial plexus.11 Therefore, if low volumes of local anesthetic are used, a more distal approach, such as the conventional ultrasound-guided supraclavicular plexus block, may miss the suprascapular nerve.
Discussion Ip and Tsui12 recently described a low interscalene approach that is similar to the superior trunk block in that the trunks, and not the roots, of the brachial plexus are targeted. Where their approach differs is that the low interscalene block is intended as an alternative to the supraclavicular plexus block for anesthesia of the upper limb distal to the shoulder. As a result, their site of needle insertion is slightly more distal. The needle is inserted through the middle scalene muscle to place the tip deeper, between the superior and middle trunks, and a larger volume of local anesthetic is injected. In contrast, the superior trunk block is intended as an alternative to the conventional ultrasound-guided
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Fig. 4 In this view, the suprascapular nerve (solid arrow), which is the first major branch of the brachial plexus, has begun to separate from the superior trunk. It will be seen to continue to move laterally as the plexus is scanned more distally. The superior trunk lies just under the deep cervical fascia (dotted line). The middle and inferior trunk are less visible in this image but lie deep to the superior trunk and immediately adjacent (lateral) to the subclavian artery. (Image courtesy of www.usra.ca)
interscalene block for anesthesia of the shoulder and may offer several theoretical advantages. First, the superior trunk has a clearly visible and welldefined connective tissue sheath which enhances resilience to needle-nerve contact. In contrast, the roots are surrounded by relatively little connective tissue and the epineurium is closely applied to the investing fascia of the interscalene groove, increasing the risk of sub-epineurial injection if visible needle-nerve contact is routinely sought.13 This may partly explain why registry data indicate that ultrasound-guided interscalene block continues to be associated with a higher risk of neurologic deficit compared with other blocks.2 Second, injury to the dorsal scapular and long thoracic nerves has recently been described in association with ultrasound-guided interscalene block.14,15 These nerves course through the middle scalene muscle at the level of the interscalene groove but are not always easy to visualize.16 The needle path in the superior trunk block does not traverse the middle scalene muscle and thus reduces the possibility of inadvertent needle trauma to these nerves. Phrenic nerve palsy is a well-recognized risk of interscalene block but has received increased attention following recent reports of persistent phrenic nerve palsy, attributed in part to inflammatory scarring, perhaps from the myotoxicity of local anesthetics.17-19 The use of lower volumes of local anesthetic in ultrasound-guided interscalene block has been shown to reduce, but not eliminate, the incidence of phrenic nerve palsy.3,4 This is not surprising given that the phrenic nerve lies within 2 mm
The superior trunk brachial plexus block
of the brachial plexus at the level of the cricoid cartilage (where it can often be seen superficial to the anterior scalene muscle).20 Nevertheless, it diverges from the brachial plexus by an additional 3mm for every 1cm that it descends into the root of the neck.20 It therefore seems prudent to inject local anesthetic as distal as possible in an attempt at further minimizing the risk of involvement of the phrenic nerve. Finally, in the 30-35% of individuals whose C5 nerve root takes an anomalous course through the anterior scalene muscle,7,8 the scanning process associated with the superior trunk block facilitates recognition of this anatomic variation and improves the chance of block success, as the C5 root inevitably joins the C6 nerve root to form the superior trunk. The main caveat to the superior trunk block is that the transverse cervical artery may lie across and superficial to the brachial plexus at this level.21 Its presence should always be excluded before commencing needle insertion by transiently releasing pressure on the probe (in case the vessel is compressed and therefore invisible) and use of colour Doppler. One of the greatest advantages of ultrasound-guided regional anesthesia has been the enhanced knowledge of anatomy that it both demands as well as provides. It has also removed our dependence on surface anatomical landmarks, and these factors have allowed our specialty to devise new block techniques and refine existing ones. Further research is planned to confirm the efficacy and safety of the technique, in particular the incidence of phrenic nerve palsy, compared with the conventional ultrasound-guided interscalene block. Acknowledgments Dr. Ki Jinn Chin is supported by a 2013-2015 Merit Award from the Department of Anesthesia, University of Toronto. Funding
This work did not receive any direct funding support.
Conflicts of interest
None declared.
References 1. Nadeau MJ, Levesque S, Dion N. Ultrasound-guided regional anesthesia for upper limb surgery. Can J Anesth 2013; 60: 304-20. 2. Sites BD, Taenzer AH, Herrick MD, et al. Incidence of local anesthetic systemic toxicity and postoperative neurologic symptoms associated with 12,668 ultrasound-guided nerve blocks: an analysis from a prospective clinical registry. Reg Anesth Pain Med 2012; 37: 478-82.
3. Lee JH, Cho SH, Kim SH, et al. Ropivacaine for ultrasoundguided interscalene block: 5 mL provides similar analgesia but less phrenic nerve paralysis than 10 mL. Can J Anesth 2011; 58: 1001-6. 4. Riazi S, Carmichael N, Awad I, Holtby RM, McCartney CJ. Effect of local anaesthetic volume (20 vs 5 ml) on the efficacy and respiratory consequences of ultrasound-guided interscalene brachial plexus block. Br J Anaesth 2008; 101: 549-56. 5. Merchant R, Chartrand D, Dain S, et al. Guidelines to the practice of anesthesia – revised edition 2014. Can J Anesth 2014; 61: 46-71. 6. Maybin J, Townsley P, Bedforth N, Allan A. Ultrasound guided supraclavicular nerve blockade: first technical description and the relevance for shoulder surgery under regional anaesthesia. Anaesthesia 2011; 66: 1053-5. 7. Sakamoto Y. Spatial relationships between the morphologies and innervations of the scalene and anterior vertebral muscles. Ann Anat 2012; 194: 381-8. 8. Gutton C, Choquet O, Antonini F, Grossi P. Ultrasound-guided interscalene block: influence of anatomic variations in clinical practice (French). Ann Fr Anesth Reanim 2010; 29: 770-5. 9. Filip P. Complex arithmetic at the brachial plexus roots. Reg Anesth Pain Med 2009; 34: 79-80. 10. Mian A, Chaudhry I, Huang R, Risk E, Tubbs RS, Loukas M. Brachial plexus anesthesia: A review of the relevant anatomy, complications, and anatomical variations. Clin Anat 2014; 27: 210-21. 11. Siegenthaler A, Moriggl B, Mlekusch S, et al. Ultrasound-guided suprascapular nerve block, description of a novel supraclavicular approach. Reg Anesth Pain Med 2012; 37: 325-8. 12. Ip VH, Tsui BC. Lower interscalene approach for elbow surgery. Can J Anesth 20013; 60: 600-1. 13. Orebaugh SL, McFadden K, Skorupan H, Bigeleisen PE. Subepineurial injection in ultrasound-guided interscalene needle tip placement. Reg Anesth Pain Med 2010; 35: 450-4. 14. Saporito A. Dorsal scapular nerve injury: a complication of ultrasound-guided interscalene block. Br J Anaesth 2013; 111: 840-1. 15. Thomas SE, Winchester JB, Hickman G, DeBusk E. A confirmed case of injury to the long thoracic nerve following a posterior approach to an interscalene nerve block. Reg Anesth Pain Med 2013; 38: 370. 16. Hanson NA, Auyong DB. Systematic ultrasound identification of the dorsal scapular and long thoracic nerves during interscalene block. Reg Anesth Pain Med 2013; 38: 54-7. 17. Pakala SR, Beckman JD, Lyman S, Zayas VM. Cervical spine disease is a risk factor for persistent phrenic nerve paresis following interscalene nerve block. Reg Anesth Pain Med 2013; 38: 239-42. 18. Hogan QH. Phrenic nerve function after interscalene block revisited: now, the long view. Anesthesiology 2013; 119: 250-2. 19. Kaufman MR, Elkwood AI, Rose MI, et al. Surgical treatment of permanent diaphragm paralysis after interscalene nerve block for shoulder surgery. Anesthesiology 2013; 119: 484-7. 20. Kessler J, Schafhalter-Zoppoth I, Gray AT. An ultrasound study of the phrenic nerve in the posterior cervical triangle: implications for the interscalene brachial plexus block. Reg Anesth Pain Med 2008; 33: 545-50. 21. Murata H, Sakai A, Hadzic A, Sumikawa K. The presence of transverse cervical and dorsal scapular arteries at three ultrasound probe positions commonly used in supraclavicular brachial plexus blockade. Anesth Analg 2012; 115: 470-3.
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CASE REPORTS / CASE SERIES
Refining the ultrasound-guided interscalene brachial plexus block: the superior trunk approach Raffinement du bloc interscale´nique e´choguide´ du plexus brachial: la voie de la branche supe´rieure David Burckett-St.Laurent, MBBS • Vincent Chan, MD • Ki Jinn Chin, MBBS Received: 14 May 2014 / Accepted: 3 September 2014 Ó Canadian Anesthesiologists’ Society 2014
Abstract Purpose The conventional ultrasound-guided interscalene block targets the C5 and C6 nerve roots at approximately the level of the cricoid cartilage where they lie in the groove between the anterior and middle scalene muscles. This technique, although effective at providing regional anesthesia of the shoulder, is associated with risks of phrenic nerve palsy, injury to the dorsal scapular and long thoracic nerves, and long-term postoperative neurologic symptoms. In this case report, we describe the ultrasoundguided superior trunk block. This procedure targets the C5 and C6 components of the brachial plexus more distally after they unite into the superior trunk but before the suprascapular nerve branches off. Clinical features We performed an ultrasound-guided superior trunk block to provide perioperative analgesia for ambulatory arthroscopic shoulder repair in a patient with moderate chronic obstructive pulmonary disease. The technique, relevant sonoanatomy of the brachial plexus, and the potential advantages of the superior trunk block are discussed.
Electronic supplementary material The online version of this article (doi:10.1007/s12630-014-0237-3) contains supplementary material, which is available to authorized users. Author contributions David Burckett-St.Laurent and Ki Jinn Chin contributed substantially to the conception and drafting of the article. David Burckett-St.Laurent, Vincent Chan, and Ki Jinn Chin contributed substantially to the design and drafting of the article. D. Burckett-St.Laurent, MBBS V. Chan, MD K. J. Chin, MBBS (&) Department of Anesthesia, Toronto Western Hospital, University of Toronto, 399 Bathurst St., Toronto, ON M5T 2S8, Canada e-mail: [email protected]
Conclusion The enhanced anatomical knowledge provided by ultrasound-guidance has allowed anesthesiologists to devise new block techniques and refine existing ones. The superior trunk block is an example of this refinement and is intended as an alternative to the conventional interscalene block for anesthesia of the shoulder. Further research is planned to confirm the efficacy and safety of the technique. Re´sume´ Objectif Le bloc interscale´nique e´choguide´ conventionnel cible les racines nerveuses C5 et C6 approximativement a` la hauteur du cartilage cricoı¨de ou` elles traversent un espace entre les muscles scale`nes ante´rieur et moyen. Bien que cette technique produise une anesthe´sie re´gionale efficace de l’e´paule, elle est associe´e a` des risques de paralysie du nerf phre´nique, de le´sion du nerf dorsal de la scapula et des nerfs thoraciques longs, ainsi qu’a` des ˆ mes neurologiques postope´ratoires a` long terme. sympto Dans ce rapport de cas, nous de´crivons un bloc e´choguide´ de la branche supe´rieure. Cette proce´dure cible les branches C5 et C6 du plexus brachial plus distalement, apre`s leur union pour former la branche supe´rieure, mais avant la division du nerf suprascapulaire. Caracte´ristiques cliniques Nous avons pratique´ un bloc e´choguide´ de la branche supe´rieure pour obtenir une analge´sie pe´riope´ratoire au cours d’une re´paration de l’e´paule par voie arthroscopique en ambulatoire chez un patient ayant une maladie pulmonaire obstructive chronique d’intensite´ mode´re´e. La technique, l’anatomie e´chographique pertinente du plexus brachial et les avantages du bloc de la branche supe´rieure sont discute´s. Conclusion L’ame´lioration des connaissances anatomiques procure´e par l’e´choguidage a permis aux anesthe´siologistes de mettre au point de nouvelles techniques de blocs et de
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raffiner celles qui existent. Le bloc de la branche supe´rieure est un exemple de ce raffinement et est vu comme une technique de remplacement du bloc interscale´nique conventionnel pour l’anesthe´sie de l’e´paule. D’autres e´tudes sont pre´vues pour confirmer l’efficacite´ et l’innocuite´ de la technique.
The interscalene block is a valuable analgesic option in shoulder surgery. It targets the C5 and C6 roots of the brachial plexus that give rise to the suprascapular nerve, axillary nerve, and lateral pectoral nerves that innervate the shoulder joint. The most common technique of ultrasoundguided interscalene block involves imaging the C5 and C6 roots at approximately the level of the cricoid cartilage, just distal to where they emerge from behind their respective transverse processes and where they lie in the groove between the anterior and middle scalene muscles (Fig. 1). The block needle is usually advanced in plane in a lateralto-medial direction through the middle scalene muscle to contact the nerve roots and inject local anesthetic around them.1 Although this is a highly effective technique, it has some limitations, including a reported incidence of three cases per 1,000 of long-term (more than six months) postoperative neurologic symptoms (most commonly paresthesia or numbness; very rarely motor weakness)2 and an ever-present risk of phrenic nerve palsy despite injection of volumes as low as 5 mL.3,4 In this case report, we describe an alternative approach to C5/C6 blockade the ultrasound-guided superior trunk block.
Case illustration Written informed consent was obtained from the patient for inclusion in this report. A 55-yr-old male was scheduled for right arthroscopic shoulder surgery (Bankart repair with remplissage procedure) as an ambulatory surgery case. He was a heavy smoker with an 80-pack-year history and daily recreational use of marijuana, with resulting moderate chronic obstructive airways disease. Pulmonary function tests revealed post-bronchodilator values of FEV1/FVC 52% and FEV1% 62%. His medications included inhaled bronchodilator therapy (budesonide, formoterol, tiotropium bromide) and a statin for hypercholesterolemia. After discussing risks and benefits, the patient agreed to receive an ultrasound-guided superior trunk block for postoperative analgesia. After applying standard monitoring,5 an ultrasoundguided superior trunk block was performed using a linear
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Fig. 1 Dissection of the right brachial plexus above the clavicle. The conventional ultrasound-guided interscalene block targets C5 and C6 roots in the interscalene groove between the middle scalene muscle (MSM) and the anterior scalene muscle (ASM), just distal to where they emerge from under the sternocleidomastoid muscle (SCM). More distally, the C5 and C6 roots rise out of the groove and unite to form the superior trunk. The probe image and the dotted rectangle indicate the probe locations for the conventional interscalene block and superior trunk block, respectively. Observe the phrenic nerve (black arrows) descending in a medial direction over the ASM away from the brachial plexus as well as the artery crossing the C7 and C8 roots. (Image adapted with permission from D. Jankovic and reproduced with permission from www.usra.ca)
high-frequency (5-12 MHz) probe and a 22G 50-mm StimuplexÒ block needle (B. Braun, Mississauga, ON, Canada). An injection of 0.25% bupivacaine 12 mL with epinephrine 0.0025 mgmL-1 was administered, and an additional 5 mL of local anesthetic was injected superficial to the middle scalene muscle to block the supraclavicular nerves (lower branches of the superficial cervical plexus supplying the ‘‘cape’’ area of the shoulder).6 The patient exhibited motor and sensory blockade at 15 min without any subjective increase in work of breathing. Ultrasound of the ipsilateral diaphragm did not show paradoxical movement, further supporting an absence of clinically significant phrenic nerve paralysis. The patient subsequently underwent a successful surgical repair under general anesthesia. His recovery was rapid and uneventful, and he was discharged four hours after emergence from anesthesia. At telephone follow-up the next day, the patient reported excellent postoperative analgesia with onset of pain evident approximately 23 hr after block completion. This was
The superior trunk brachial plexus block b Fig. 2 A sequential series of images of the brachial plexus above the
clavicle from proximal to distal. (A) A transverse oblique view of the C5 (smaller hypoechoic circle) and C6 (larger circle) in the most proximal part of the interscalene groove, just under the lateral border of the sternocleidomastoid muscle (SCM). (B) The C6 root has split in characteristic fashion into two separate hypoechoic circles. The phrenic nerve (arrow) is visible in this individual on the surface of the anterior scalene muscle (ASM). (C) The C7 root has entered the interscalene groove, lying deep to C5 and C6. (D) The C5 and C6 roots have coalesced into the superior trunk, which has a well-defined hyperechoic boundary. The block needle is advanced in plane under the deep cervical fascia overlying the middle scalene muscle (MSM) until its tip is adjacent to the lateral aspect of the superior trunk. Injection here should produce spread around, but not within, the superior trunk. (Image courtesy of www.usra.ca)
transverse process (Fig. 2A) and entering the groove between the anterior and middle scalene muscles (Fig. 2B and 2C). It is noteworthy that, in up to 30-35% of individuals, the C5 nerve root takes an anomalous course over or through the anterior scalene muscle rather than the interscalene groove (Fig. 3).7,8 Ultrasonographic identification of this anomaly is complicated by the fact that the C6 nerve root almost always splits into two hypoechoic bundles within the interscalene groove and can thus be mistaken for two separate roots (Fig. 2B and 2C; Fig. 3).8 It is vital to recognize this normal splitting of C6, as injection between these two structures would constitute an intraneural injection. The C5 and C6 roots become increasingly superficial within the interscalene groove and eventually unite to form the superior trunk (Fig. 1), which is visible as a single complex structure with a hyperechoic connective tissue boundary lying just below the prevertebral (deep cervical) fascia (Fig. 2D). More distally in the root of the neck, the C8 and T1 roots unite to form the inferior trunk, while the C7 root forms the middle trunk.9 The trunks bifurcate into anterior and posterior divisions posterior to the clavicle,10 and these comprise the complex ‘‘bunch of grapes’’ appearance of the brachial plexus as it crosses the first rib in the ultrasonographic view that is used in the supraclavicular block.
Technical description of the superior trunk block
adequately controlled with oral analgesics. He had no respiratory or neurological symptoms.
Review of anatomy and sonoanatomy The C5 and C6 roots are visible on ultrasound as dark hypoechoic circles emerging from their respective
The C5 and C6 nerve roots are identified within the interscalene groove, but instead of targeting them at this level, they are traced distally to where they coalesce into the superior trunk. The block needle is advanced in plane in a lateral-to-medial direction under the deep cervical fascia and superficial to the middle scalene muscle until the tip is just adjacent to the lateral boundary of the superior trunk (Fig. 2D). An out-of-plane approach may also be used if preferred. Injection of local anesthetic at this point will
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Fig. 3 An example of an anomalous course of the C5 root, which, in this case, travels through and then superficial to the anterior scalene muscle (ASM), remaining outside the interscalene groove. As the brachial plexus is followed more distally, C5 will be seen to unite eventually with C6 to form the superior trunk. Observe that both the C6 and C7 roots in this individual have a ‘‘double bundle’’ appearance. (Image courtesy of www.usra.ca)
hydrodissect the tissue plane around the superior trunk, and 10-15 mL will spread around it with minimal need for needle repositioning (see Video; available as Electronic Supplemental Material). It is crucial to target the superior trunk proximal to the takeoff of the suprascapular nerve. This nerve is identified as a small hypoechoic circle that separates from the lateral aspect of the superior trunk (Figure 4) and courses laterally under the omohyoid muscle away from the brachial plexus.11 Therefore, if low volumes of local anesthetic are used, a more distal approach, such as the conventional ultrasound-guided supraclavicular plexus block, may miss the suprascapular nerve.
Discussion Ip and Tsui12 recently described a low interscalene approach that is similar to the superior trunk block in that the trunks, and not the roots, of the brachial plexus are targeted. Where their approach differs is that the low interscalene block is intended as an alternative to the supraclavicular plexus block for anesthesia of the upper limb distal to the shoulder. As a result, their site of needle insertion is slightly more distal. The needle is inserted through the middle scalene muscle to place the tip deeper, between the superior and middle trunks, and a larger volume of local anesthetic is injected. In contrast, the superior trunk block is intended as an alternative to the conventional ultrasound-guided
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Fig. 4 In this view, the suprascapular nerve (solid arrow), which is the first major branch of the brachial plexus, has begun to separate from the superior trunk. It will be seen to continue to move laterally as the plexus is scanned more distally. The superior trunk lies just under the deep cervical fascia (dotted line). The middle and inferior trunk are less visible in this image but lie deep to the superior trunk and immediately adjacent (lateral) to the subclavian artery. (Image courtesy of www.usra.ca)
interscalene block for anesthesia of the shoulder and may offer several theoretical advantages. First, the superior trunk has a clearly visible and welldefined connective tissue sheath which enhances resilience to needle-nerve contact. In contrast, the roots are surrounded by relatively little connective tissue and the epineurium is closely applied to the investing fascia of the interscalene groove, increasing the risk of sub-epineurial injection if visible needle-nerve contact is routinely sought.13 This may partly explain why registry data indicate that ultrasound-guided interscalene block continues to be associated with a higher risk of neurologic deficit compared with other blocks.2 Second, injury to the dorsal scapular and long thoracic nerves has recently been described in association with ultrasound-guided interscalene block.14,15 These nerves course through the middle scalene muscle at the level of the interscalene groove but are not always easy to visualize.16 The needle path in the superior trunk block does not traverse the middle scalene muscle and thus reduces the possibility of inadvertent needle trauma to these nerves. Phrenic nerve palsy is a well-recognized risk of interscalene block but has received increased attention following recent reports of persistent phrenic nerve palsy, attributed in part to inflammatory scarring, perhaps from the myotoxicity of local anesthetics.17-19 The use of lower volumes of local anesthetic in ultrasound-guided interscalene block has been shown to reduce, but not eliminate, the incidence of phrenic nerve palsy.3,4 This is not surprising given that the phrenic nerve lies within 2 mm
The superior trunk brachial plexus block
of the brachial plexus at the level of the cricoid cartilage (where it can often be seen superficial to the anterior scalene muscle).20 Nevertheless, it diverges from the brachial plexus by an additional 3mm for every 1cm that it descends into the root of the neck.20 It therefore seems prudent to inject local anesthetic as distal as possible in an attempt at further minimizing the risk of involvement of the phrenic nerve. Finally, in the 30-35% of individuals whose C5 nerve root takes an anomalous course through the anterior scalene muscle,7,8 the scanning process associated with the superior trunk block facilitates recognition of this anatomic variation and improves the chance of block success, as the C5 root inevitably joins the C6 nerve root to form the superior trunk. The main caveat to the superior trunk block is that the transverse cervical artery may lie across and superficial to the brachial plexus at this level.21 Its presence should always be excluded before commencing needle insertion by transiently releasing pressure on the probe (in case the vessel is compressed and therefore invisible) and use of colour Doppler. One of the greatest advantages of ultrasound-guided regional anesthesia has been the enhanced knowledge of anatomy that it both demands as well as provides. It has also removed our dependence on surface anatomical landmarks, and these factors have allowed our specialty to devise new block techniques and refine existing ones. Further research is planned to confirm the efficacy and safety of the technique, in particular the incidence of phrenic nerve palsy, compared with the conventional ultrasound-guided interscalene block. Acknowledgments Dr. Ki Jinn Chin is supported by a 2013-2015 Merit Award from the Department of Anesthesia, University of Toronto. Funding
This work did not receive any direct funding support.
Conflicts of interest
None declared.
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