ultrasound-guided interscalene block · block dr matthieu vierula1 ... position the patient and...

Ultrasound-Guided InterscaleneBlock

Dr Matthieu Vierula1†, Dr Joshua Robert2, Dr Patrick Wong3, DrJason McVicar3

1Anesthesiology Resident, University of Ottawa, The Ottawa Hospital, Canada2Regional Anesthesia Fellow, University of Ottawa, The Ottawa Hospital, Canada3Assistant Professor, University of Ottawa, The Ottawa Hospital, Canada

Edited by: Dr Su Cheen Ng, Consultant Anaesthesiologist, University College Hospital

London, UK; Dr Gillian Foxall, Consultant Anaesthetist, Royal Surrey County Hospital,

Guildford, UK

†Corresponding author email: [email protected]

Published 19 March 2019

KEY POINTS

� Ultrasound-guided interscalene brachial plexus block can provide dense surgical anaesthesia, and/or intra- and

postoperative analgesia, for shoulder surgery.� Patient selection is particularly important for interscalene block safety, since the frequently associated phrenic nerve

block can cause significant respiratory distress in patients with preexisting respiratory disease.� Practitioners should use dynamic ultrasound scanning and colour Doppler to correctly identify the brachial plexus

roots in the interscalene groove and to avoid inadvertent intravascular injection.� Tracking the needle tip, assessing the local anaesthetic spread, and maintaining a cautious approach to the nerve

roots are fundamental to reducing the risk of complications such as nerve injury or local anaesthetic toxicity.

INTRODUCTION

The ultrasound-guided interscalene block (ISB) has a faster onset time and longer duration than the nerve-stimulation

technique, and it produces surgical anaesthesia more reliably for the same volume of local anaesthetic.1 Likewise, lower

volumes of local anaesthetic are needed for an effective block.2 An ultrasound-guided technique can also decrease the

incidence of hemidiaphragmetic paresis.3 However, the incidence and severity of postoperative neurological symptoms are

similar between both techniques.4 A periplexus approach to the ultrasound-guided ISB, with deposition of local anaesthetic in

the potential space between middle scalene (MS) muscle and brachial plexus sheath, produces the same quality of block as

the classic intraplexus approach (where the needle tip is placed between individual nerve roots).5,6 Performing the block

outside the brachial plexus sheath under ultrasound visualization, using a periplexus approach, may reduce the risk of nerve

injury.7

ANATOMY

Brachial Plexus

� The brachial plexus innervates the shoulder and upper limb (Figure 1). The roots originate from the ventral rami of cervical (C)

spinal nerves C5 through C8 and the first thoracic spinal nerve, T1 (Figure 2).8 Variations include having a ‘‘prefixed’’ plexus

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that originates from C4 through C8 or a ‘‘postfixed’’ plexus that originates from C6 through C8 and T1 to T2.9 A study of

anatomic variation in human fetuses identified a ‘‘prefixed’’ plexus in 25.5% of cases and a ‘‘postfixed’’ plexus in 2.5% of

cases.10

� The brachial plexus’s upper roots are typically found in the ‘‘interscalene groove’’ between the anterior scalene (AS) and MS

muscles, although the C5 root may be anterior to the AS and both C5 and C6 roots may pass through the AS.11

� The C6 nerve root often bifurcates into 2 fascicles, within a common epineurium, before forming the upper trunk with the C5

nerve root.12

Adjacent Structures

� The cervical plexus provides sensory innervation to the ‘‘shoulder cape’’ via the supraclavicular nerve (C3-4).� The cervical plexus provides motor innervation to the ipsilateral diaphragm via the phrenic nerve (C3-5). The phrenic nerve

passes between the AS and MS, and then descends on the anterior surface of the AS into the thoracic cavity.� The recurrent laryngeal nerve provides motor innervation to all but one of the intrinsic laryngeal muscles, the cricothyroid

muscle, which is innervated by a branch of the superior laryngeal nerve.

Figure 1. Sensory innervation of the upper extremity. Source: Henry Vandyke Carter [Public domain], via Wikimedia Commons: https://upload.

wikimedia.org/wikipedia/commons/d/de/Gray812and814.PNG.





� The sympathetic nerve fibres innervating the head exit the spinal cord at upper thoracic levels (T1) before entering the

sympathetic chain and ascending to the superior cervical ganglion.

� The long thoracic and dorsal scapular nerves originate from the proximal brachial plexus and frequently pass through the MS

at the same level and slightly posterior to the C6 nerve root.13

� The carotid and vertebral arteries and the internal and external jugular veins follow a course perpendicular, and in proximity, to

the brachial plexus nerve roots.

� The subclavian artery runs parallel to the brachial plexus nerve roots at the level of C8 and T1. At the level of the trunks, the

brachial plexus is posterior and cephalic in relation to the artery.14

� The transverse cervical artery, which arises from the thyrocervical trunk of the subclavian artery, crosses anterior to the

scalene muscles.

� The apex of the lungs extends into the root of the neck, reaching up to 4 cm above the middle third of the clavicle.

Ultrasound

� At the interscalene groove, the C5-7 nerve roots are better visualized than C8 and T1 due to the depth and cephalo-caudad

position of each nerve root. The brachial plexus’s roots appear as round homogenous hypoechoic (dark) structures (Figure 3),

not the classic honeycomb pattern that is seen distally in the brachial plexus. This difference is due to the high density of

conducting axons and relatively little hyperechoic connective tissue found elsewhere in the body. Differentiating the nerve

roots from other adjacent hypoechoic structures, such as blood vessels, requires careful attention and can be aided by the

routine use of colour Doppler. It is also more difficult to capture all the brachial plexus nerve roots in the same image due to

their varied angulation upon exiting the spinal cord.

� The brachial plexus can be readily identified at the supraclavicular level where the trunks run parallel to each other and are

most frequently lateral to the subclavian artery, though anatomical variations exist where the superior trunks may be anterior

or medial the artery (Figure 4).14 The roots can then be located using the ‘‘traceback’’ method, sliding the transducer

cephalad while maintaining visualization of the plexus up to the interscalene groove (Figure 5).

� The ‘‘stoplight sign’’ is a frequently cited name for the typical sonographic appearance of 3 root structures aligned vertically in

the interscalene groove. The 3 structures most often represent, from cephalad to caudal: the C5 root, the upper fascicle of C6,

and the lower fascicle of C6.12

Figure 2. Anatomic representation of the embryonic limb organization of the brachial plexus. Copyright Elsevier Netter Images. Used with

permission.





� Identifying the cervical level with ultrasound is based on the difference between C6 (Figure 6) and C7 (Figure 7) transverse

process anatomy. The C7 transverse process is identified by the small anterior tubercle on ultrasound, and it can be

compared to C6 by sliding the transducer between adjacent vertebrae (Figure 8).15

� The long thoracic and dorsal scapular nerves appear as discrete hyperechoic structures with a hypoechoic centre within the

MS muscle.13

INTERSCALENE BLOCK

Indications

The ISB provides reliable anaesthesia and analgesia to the shoulder and proximal arm because it consistently blocks the C5-6

nerve roots.16,17 With higher volumes of local anaesthetic, the block also affects the superficial cervical plexus including the

supraclavicular nerve, providing a sensory block to the ‘‘shoulder cape.’’

Contraindications

General contraindications to regional anaesthesia and specific contraindications to the ISB are presented in Table 1.

Determining whether or not the ISB is contraindicated in a patient requires a thorough understanding of the side effects and

complications that are specific to this block.

Figure 4. Ultrasound image of supraclavicular view of the brachial plexus (BP) and subclavian artery (SA).

Figure 3. Anatomic representation and ultrasound image of the interscalene groove. Copyright American Society of Regional Anesthesia and

Pain Medicine. Used with permission.





Side Effects and Complications

The side effects and complications related to ISB are presented in Table 2. Compared to other peripheral nerve blocks, the ISB

carries the highest risk of neurological injury. The estimated rate of occurrence of neuropathy after ISB is 2.84 per 100

patients.18 Depending on the volume used, the incidence of ipsilateral phrenic nerve block is up to 100%.19 Contralateral or

severe bilateral respiratory impairments are thus contraindications to ISB (eg, chest trauma, pneumonectomy, pneumothorax,

severe chronic obstructive pulmonary disease). Similarly, ISB is contraindicated in the presence of contralateral phrenic nerve

deficit, since blocking the functional phrenic nerve may result in severe respiratory distress or respiratory arrest. Preexisting

unilateral vocal cord paralysis also limits the use of ISB on the contralateral side because of the risk of recurrent laryngeal nerve

block which may precipitate glottic obstruction.

TECHNIQUE

Equipment

� Standard physiologic monitors (electrocardiogram, pulse oximeter, noninvasive blood pressure)

� Resuscitation equipment including 20% lipid emulsion (Intralipid)

� Skin antiseptic, preferably chlorhexidine/alcohol based

� Sterile gloves, drapes, and transducer cover

� Ultrasound machine with a high-frequency linear transducer

� Short-bevel regional block needle (eg, 50 mm, 22 gauge)

� Normal saline or 5% dextrose solution (if using nerve stimulation in addition to ultrasound guidance)

� Short-acting local anaesthetic such as lignocaine for skin infiltration (1% or 2%)

� Local anaesthetic solution for plexus block

Safe and successful regional anaesthesia also requires a skilled assistant.

Figure 6. Cervical vertebrae anatomy. Source: Henry Vandyke Carter [Public domain], via Wikimedia Commons: https://upload.wikimedia.org/

wikipedia/commons/3/3c/Gray84.png

Figure 5. Ultrasound image of the interscalene groove. AS indicates anterior scalene; MS, middle scalene; SCM, sternocleidomastoid; TP,

transverse process of the 7th cervical vertebra; C5-7, 5th to 7th cervical nerve roots; And VA, vertebral artery.





Positioning

The patient can be positioned supine with their head rotated towards the contralateral side, or in the lateral decubitus position

with the block side up. The operator can position themselves at the patient’s side or at the head of the bed. Proper bed height

and ergonomics are key to the safe conduct of regional anaesthesia.

Approach and Scanning

� Gain intravenous access, apply standard monitoring, and perform institutional preprocedural safety checklist (see Table 3).20

Figure 8. A. Ultrasound image of C6 transverse process. B. Ultrasound image of C7 transverse process. AS indicates anterior scalene; MS,

middle scalene; SCM, sternocleidomastoid; C5-7, 5th to 7th cervical nerve roots; and TP6-7; 6th and 7th cervical vertebrae transverse

processes.

Figure 7. Seventh cervical vertebra anatomy. Source: Henry Vandyke Carter [Public domain], via Wikimedia Commons: https://upload.

wikimedia.org/wikipedia/commons/c/cf/Gray89.png.





� Position the patient and perform skin preparation of the neck and supraclavicular area with chlorhexidine/alcohol before

applying sterile drapes and covering the transducer with a sterile cover.� Position the transducer in the supraclavicular fossa just cephalad and parallel to the clavicle to identify the subclavian artery,

first rib, lung pleura and the brachial plexus trunks.� Using the ‘‘traceback’’ method, follow the nerve trunks back up to the interscalene groove by sliding the transducer cephalad

while maintaining visualization of the plexus.� Once the brachial plexus nerve roots have been identified in the interscalene groove, confirm the cervical level based on

transverse process anatomy. Use colour Doppler to identify vascular structures, paying specific attention to avoid the

vertebral artery and the transverse cervical artery.�When visualizing the ‘‘stoplight sign,’’ the C6 nerve root’s fascicles are correctly identified by tracing the nerve root proximal to

its bifurcation where the nerve exits the intervertebral foramen.� Confirm appropriate probe position before attempting needle puncture. The probe should be oriented transversely across the

lateral neck, overlying the sternocleidomastoid and scalene muscles, at approximately the level of the cricoid cartilage.

Block Conduct—Periplexus Interscalene Block

� Confirm the identity of critical landmarks: AS, MS, and the C5 and C6 roots within the interscalene groove.� Infiltrate the skin with 1 to 3 mL of local anaesthetic.� Advance the block needle in plane through skin and MS towards the C5 and C6 roots in the interscalene groove (Figure 9).� As the needle traverses MS, be careful to avoid injuring the long thoracic and dorsal scapular nerves.� Advance the needle through the MS and stop at the border of its fascial layer with the hyperechoic fascia covering the brachial

plexus.� A subtle ‘‘pop’’ sensation may be appreciated when the needle tip enters the interscalene groove. The needle tip does not

need to pierce the brachial plexus sheath (periplexus approach). This approach is advised to reduce the risk of nerve injury.� Aspirate to rule out an intravascular needle position and inject 1 mL of saline or 5% dextrose to confirm deposition between

the fascial layers.� To avoid intraneural injection, only inject with low pressures, observe the nerve roots to rule out nerve expansion (which

indicates intraneural injection), and communicate with the patient to rule out paresthesias during needle advancement.� If the injectate spreads posteriorly along the needle tract within MS, advance another 1 to 2 mm, being careful to avoid

piercing the nerve roots with the needle.� Correct injectate deposition will appear on ultrasound as the plexus being pushed medially with hypoechoic spread adjacent to

the nerve roots (Figure 9).

Side effects Complications

Horner’s syndrome (ptosis, miosis, anhydrosis)

Phrenic nerve block (dyspnea/asymptomatic)

Recurrent laryngeal nerve block (dysphonia)

Epidural or subarachnoid injection

Hematoma

Intravascular injection

Local anaesthetic toxicity

Pneumothorax

Postoperative neurological symptoms

Injury to long thoracic or dorsal scapular nerves

Injury to the brachial plexus nerve roots

Table 2. Side Effects and Complications of the Interscalene Block

General Specific

Absolute

Local anaesthetic allergy

Patient refusal

Infection at the site of injection

Lack of skilled assistance

Lack of resuscitation equipment

Contralateral respiratory impairments

Chest trauma

Pneumothorax

Pneumonectomy

Phrenic nerve palsy

Recurrent laryngeal nerve palsy

Severe bilateral lung disease (eg, COPD)

Relative

Systemic infection

Coagulopathy

Preexisting injury of the brachial plexus or distal nerves

Table 1. Contraindications to the Interscalene Block





� For block success, local anaesthetic must be visualized within the correct tissue plane of the interscalene groove. However,

complete circumferential spread around the plexus is not necessary. Our practice is to scan proximally and distally from the

injection site several times over the course of the injection to confirm correct deposition not only in the plane of our needle, but

also along the course of the plexus.

� Once satisfied with needle position, switch to local anaesthetic. Inject the total desired volume in 3- to 5-mL increments, while

continuing to aspirate intermittently to rule out an intravascular injection and confirming low injection pressures.

Regional Block Preprocedural Safety Checklist

1) Patient is identified by 2 criteria.

2) Allergies and anticoagulation status are reviewed.

3) Surgical procedure/consent is confirmed with laterality noted when applicable.

4) Block plan is confirmed, site is marked.

5) Necessary equipment is present, drugs/solutions are labelled.

6) Resuscitation equipment is immediately available: airway devices, suction, vasoactive drugs, lipid emulsion.

7) Appropriate monitors are applied, intravenous access is established, sedation and supplemental oxygen are provided

if indicated.

8) Aseptic technique is used: hand cleansing is performed, mask and sterile gloves are used.

9) ‘‘Time out’’ is performed before needle insertion for each new block site if the position is changed or separated in time

or performed by another team.

Table 3. Example of a Preblock Safety Checklist, from Mulroy et al20

Figure 9. A. Interscalene block preinjection. B. Interscalene block with needle tip outside the brachial plexus sheath. C. Interscalene block final

local anesthetic spread (blue) around brachial plexus. AS indicates anterior scalene; MS, middle scalene; SCM, sternocleidomastoid; TP7,

transverse process of 7th cervical vertebra; yellow circles 5 to 7, brachial plexus nerve roots; LA, local anaesthetic; and blue, local anaesthetic

spread. Note: The images demonstrate the common finding of a C6 nerve root that has divided into upper and lower fascicles.





� Usual doses of the block are 15 to 30 mL of 0.5% bupivacaine or ropivacaine consistent with the overall local anaesthetic

dosing of less than 2.5 mg/kg.

Continuous Catheter

A perineural catheter can be placed to extend the duration of postoperative analgesia. Compared to single shot ISB alone, the

continuous infusion reduces pain on the first postoperative day.21 Some institutions, including our own, have set up ambulatory

peripheral nerve block catheter programs. Most of our patients undergoing rotator cuff repair and shoulder arthroplasty are

managed with ambulatory interscalene catheters. Numerous peripheral nerve block catheter kits are commercially available, as

well as infusion pumps designed for outpatients. Our standard protocol is to infuse the catheter with 0.2% ropivacaine at 5 mL

per hour, with a patient-controlled bolus option of 5 mL every 30 minutes. Patients are discharged home with 250-mL bags of

ropivacaine, which lasts up to 48 hours depending on bolus usage. The technical details of interscalene catheter insertion are

beyond the scope of this tutorial. The success of an ambulatory catheter program depends greatly on appropriate patient

selection, patient training on anticipated effects and potential complications, and a robust follow-up system for troubleshooting.

For further reading on peripheral nerve blocks for ambulatory surgery, we suggest the reviews by Salinas and Joseph22 and by

Swenson et al.23

SUMMARY

� The ISB consistently blocks the C5-6 nerve roots, providing reliable anaesthesia and analgesia to the shoulder and

proximal arm.� Common side effects of ISB include hemidiaphragm paresis and recurrent laryngeal nerve block. These side effects

are well tolerated in most patients but can cause severe respiratory distress in the presence of respiratory disease or

contralateral lesions. Therefore, patient screening and selection is of paramount importance for ISB safety.� Ultrasound identification of the nerve roots at the interscalene groove is facilitated by tracing the brachial plexus

proximally from the supraclavicular level.� Tracing individual nerve roots proximally to the vertebrae allows for cervical-level identification by comparing

transverse process anatomy: the C7 transverse process does not have a prominent anterior tubercle.� We advocate the use of a periplexus approach: position the needle tip in the potential space between the MS and

brachial plexus sheath for safe and effective local anaesthetic deposition.

ACKNOWLEDGEMENTS

Dr Christopher Ramnanan kindly reviewed the anatomy section.

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