Supraclavicular Block
The primary ventral rami of C5 and C6 unite to form the upper trunk above the subclavian artery, C7 becomes the middle trunk and C8 and T1 unite to form the lower trunk. Both the brachial plexus and the subclavian artery lie on top of the first rib. The brachial plexus is located lateral and posterior to the subclavian artery. The subclavian vein and anterior scalene muscle are found medial to the subclavian artery. The pleura is usually found within 1-2 cm from the brachial plexus.
The supraclavicular approach to the brachial plexus at the level of the nerve trunks or divisions was first described by Kulenkampf. However, the original technique was associated with a high incidence of pneumothorax. Although subsequent modification of this technique has lowered the complication rate, performance of this block without visual guidance is generally not recommended for outpatients.
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1 = anterior scalene muscle
2 = middle scalene muscle
CL = clavicle
FR = first rib
SA = subclavian artery
SV = subclavian vein |
- After skin and transducer preparation (see transducer preparation section), place a linear 38-mm, high frequency 10-15 MHz transducer firmly over the supraclavicular fossa in the coronal oblique plane to obtain the best possible transverse view of the subclavian artery and brachial plexus.
- Position the patient supine with the head slightly turned to the contralateral side.
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- Optimize machine imaging capability by selecting the appropriate depth of field (within 2-3 cm), focus range and gain.
- Visualize the trunks or divisions in the transverse view (short axis). Nerves in the supraclavicular region appear hypoechoic and are round or oval. The brachial plexus is located lateral and posterior to the pulsatile subclavian artery and superior to the first rib.
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Arrowheads = trunks/divisions of the brachial plexus
C = clavicle
FR = first rib
SA = subclavian artery
SAM & SMM = scalenus anterior & medius muscles
SV = subclavian vein
White box = scanned area |
- Perform a systematic anatomical survey from medial to lateral and superficial to deep.
- The brachial plexus (trunks) is generally easy to locate in this region. The subclavian artery serves as an easily identifiable reference point to locate the brachial plexus.
- First locate the subclavian artery.
- The subclavian vein is found more medially.
- The anterior scalene muscle inserts onto the first rib between these 2 vessels.
- Identify the hyperechoic first rib lying deep to the vessels and its bony shadow.
- Identify the pleura and compare it with the hyperechoic first rib. Note air artifact, the “comet tail” sign and pleura sliding movement during respiration.
- Note the skin-to-first rib and skin-to-pleura distance.
- The brachial plexus is consistently found lateral and posterior to the subclavian artery and above the first rib.
- Ultrasound guided supraclavicular block is considered an INTERMEDIATE skill level block because real time observation of needle tip location during needle advancement is critical.
- The In Plane (IP) approach is strongly recommended for this block. It is important to track the needle tip in real time to avoid inadvertent pleural puncture.
In Plane Lateral to Medial Approach
- For the IP approach, insert a 5 cm 22G insulated block needle on the outer (lateral) end of the ultrasound transducer after skin local anesthetic infiltration. Advance the needle along the long axis of the transducer in the same plane as the ultrasound beam. In this way, the needle shaft and tip can be visualized in real time as the needle is advanced towards the target nerves.
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- Confirm the identity of the nerves by electrical stimulation if desired. Useful stimulation endpoints for surgery proximal to the elbow are biceps and triceps twitches but aim to get hand muscle twitches for surgery distal to the elbow.
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Arrows = block needle
Arrowheads = nerves
SA = subclavian artery |
- Note that this procedure is unique and is dramatically different from conventional supraclavicular techniques. With one hand holding the transducer and the other holding the needle, the needle is advanced in a lateral to medial direction starting from the outer edge of the transducer.
- Observe the pattern of local anesthetic spread around the target nerves in real time during injection (hydro dissection and distention technique). If local anesthetic spread is deemed inadequate, reposition the needle before administering the remaining local anesthetic dose.
- Aim to deposit most of the local anesthetic bolus immediately above the first rib and next to the subclavian artery to anesthetize the lower trunk if anesthesia is intended for the distal limb.
- The usual volume of local anesthetic injection is between 25 and 40 mL.
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Pre-injection
Arrowheads = nerve trunks/divisions
SA = subclavian artery |
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Post-injection
Lateral to medial needle approach
Arrowheads = local anesthetic spread among nerve trunks
SA = subclavian artery |
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Post-injection
Lateral to medial needle approach
Arrows = block needle
Arrowheads = local anesthetic spread
SA = subclavian artery |
Nerve Localization
1. Transducer Angle
The transducer should be angled in different angles until an optimal image of the subclavian artery (SA), brachial plexus (arrowheads), first rib (FR) and pleura (PL) is obtained.
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Figure A shows transducer in proper position. The structures of interest are clearly visualized. |
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Arrowheads = brachial plexus
FR = first rib
PL = pleura
SA = subclavian artery |
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Figure B shows that the transducer is angled too anteriorly. None of the structures of interest are clearly visualized. |
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Figure C shows that the transducer is angled too posteriorly. The subclavian artery and the brachial plexus are now visualized oblique and the view is not optimal. |
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Arrowheads = brachial plexus
SA = subclavian artery
PL = pleura |
2. Suprascapular Artery and Transverse Cervical Artery
Hypoechoic vessels may be seen in transverse or longitudinal section among the nerve trunks/divisions in the supraclavicular region. Most common is the suprascapular artery or the transverse cervical artery. Because of similarity in appearance (both hypoechoic), it is important to differentiate the vascular structures from the nerve structures by using color Doppler. This is crucial to avoid targeting small arteries mistaken as nerves.
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Hypoechoic nodular structures in the supraclavicular region that resemble nerves (arrowheads).
Arrowheads = nerves
SA = subclavian artery |
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Color Doppler demonstrates that one of the hypoechoic nodules is a small artery (blue).
SA = subclavian artery |
Needle Insertion
Irrespective of the needle approach, it is paramount for the operator to identify the pleura and observe needle advancement in real time to avoid pleural puncture.
1. In Plane Medial to Lateral Approach
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However, the subclavian artery can often obstruct access to the medial and inferior portion of the nerve trunks or divisions of the brachial plexus. It may be necessary to use the needle to move the artery out of its path of penetration in some cases.
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Pre-injection
Arrowhead = nerves
SA = subclavian artery
FR = first rib |
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Post-injection
Medial to Lateral Needle Approach
Arrows = block needle
Arrowhead = nerves
SA = subclavian artery
LA = local anesthetic |
2. Oblique Posterior to Anterior Approach
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2) anterior to posterior, as opposed a single medial to lateral orientation when the transducer is held parallel to the clavicle. The oblique angle can enhance nerve visualization because the brachial plexus is located both lateral and posterior to the subclavian artery.