Infraclavicular Block
At the infraclavicular level, the cords of the brachial plexus are arranged around the second part of the axillary artery. Immediately medial to the coracoid process, the lateral cord of the plexus lies superior and lateral, the posterior cord lies posterior and the medial cord lies posterior and medial to the axillary artery.
Anterior to the brachial plexus are the pectoralis major and minor muscles. Posterior to the brachial plexus in this region is the scapula. The axillary vein is commonly located caudad and medial to the axillary artery.
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AA & AV = axillary artery & vein
CL = clavicle
CP = coracoid process
BP = cords of brachial plexus
PMiM = pectoralis minor muscle
Pectoralis major muscle is not shown in this picture |
- Position the patient supine with the arm to be blocked resting comfortably on the patient's side.
- After skin and transducer preparation, a linear 7 MHz transducer is applied immediately medial to the coracoid process (COR) underneath the clavicle in a parasagittal plane to obtain the best possible transverse view of the axillary vessels and cords.
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Transducer over right infraclavicular coracoid region |
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- Optimize machine imaging capability by selecting the appropriate depth of field (usually within 3-5 cm), focus range and gain.
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AA = axillary artery
Arrowheads = cords
AV = axillary vein
PMM & PMiM = pectoralis major & minor muscles
White box = scanned area
Yellow ring = location of cords of the brachial plexus |
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- Perform a systematic anatomical survey from superficial to deep. The pectoralis major and minor muscles are most superficial and easily identified.
- Move the transducer cephalad to view the clavicle (optional) and laterally to view the coracoid process (optional).
- Identify the axillary artery and vein deep to the pectoralis minor muscle. The vein is almost always caudad to the artery.
- Look for hyperechoic nerve structures cephalad, posterior and caudad to the axillary artery.
- Hyperechoic density posterior to the axillary artery can be due to "acoustic enhancement", an artifact generated when beam crosses a vessel with little acoustic impedance. Angle (tilt) the transducer slightly in the parasagittal plane to check if this hyperechoic structure stays in the same location. If it does not, this is not likely to be a nerve structure.
NEEDLE INSERTION INPLANE APPROACH
Ultrasound guided infraclavicular block is considered an INTERMEDIATE skill level block because this is a deeper block.
The In Plane (IP) approach is recommended to visualize the needle shaft and tip movement during needle advancement.
In-Plane Cephalad to Caudad Approach
- After skin and transducer preparation, a 5-7 cm 18-22 G insulated needle is inserted below the clavicle depending on the depth. A larger bore needle is preferred when the nerves are deep to facilitate visualization. Advance the needle at a 45-60 degree angle from the cephalad end of the ultrasound transducer along its long axis in the caudad direction.
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Arrows = block needle
AA = axillary artery
LA = local anesthetic
Note needle and local anesthetic posterior to artery |
- The goal is to deposit local anesthetic around all the 3 cords of the brachial plexus. Local anesthetic injected posterior to the axillary artery resulting in a U shape spread around the artery is associated with complete blockade of the arm, forearm and hand.
- Consistent success is associated with local anesthetic spread posterior to the axillary artery and a radial nerve type stimulation while inconsistent block is associated with spread anterior to the axillary artery and a median nerve type stimulation (Reg Anesth Pain Med 2007;32:130).
- In practice, it is best to inject the first 10-15 mL of local anesthetic posterior to the artery in the 6 0'clock position (posterior cord). Then inject further as the needle is withdrawn to the 9 o'clock position (lateral cord).
- If spread to the 3 o'clock position is deemed inadequate, it may be necessary to separately place the block needle between the axillary artery and vein to access the medial cord. In our experience, this maneuver is seldom necessary.
- The usual local anesthetic volume is 30-40 mL for this blockade but effective block can be achieved with a smaller local anesthetic volume. The minimum effective local anesthetic dose for this procedure has not been determined.
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Post-injection
Note: circumferential local anesthetic spread (arrowheads, hypoechoic ring) around the axillary artery (AA) |
Nerve Localization
1. Anatomical Variations in the Coracoid Region
There is wide anatomical variation of the brachial plexus cord locations in the lateral infraclavicular region (medial to the coracoid process) as shown below.
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A = axillary artery
L = lateral cord
M = medial cord
P = posterior cord
V = axillary vein
Picture from Sauter Anesth Analg 2006; (103): 1574-1576 |
Also, it is important to note that there may be only 2 cords and not 3 in this region due to anatomical variations.
2. The Arm Abduction Maneuver
Arm abduction to 90 degrees will stretch the brachial plexus and make it taut. This will bring the 3 cords closer together and will enhance nerve visualization.
Arm by the Side
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Arrowheads = nerves
AA & AV = axillary artery & vein |
Arm Abduction
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Arrowheads = nerves
AA & AV = axillary artery & vein |
3. Use of a Small Curved Transducer
A good alternative is to use a small curved transducer for infraclavicular scanning since it provides a wider field of view and more space for needle insertion.
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Figure A shows a sonogram of the infraclavicular region captured by a linear 12 MHz transducer. Note the field of view is narrow. The target nerves (arrowheads) are within 3 cm from the skin surface.
AA & AV = axillary artery & vein |
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Figure B shows a sonogram of the same region captured by a curved 8 MHz transducer. Note the field of view is wider.
Arrowheads = nerves
AA & AV = axillary artery & vein |
Needle Insertion
1. Visualizing the Needle Tip
Visualization of the block needle can be challenging due to a steep angle of insertion (> 45 degrees). One way to accurately locate the needle tip is to tilt the needle tip superficially (i.e., angle anteriorly in this case). If the needle tip is posterior to the axillary artery (6 o'clock position), one will see lifting of the artery anteriorly. If the needle tip is at the 9 o'clock position, tilting the needle will push the artery caudad.
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A. Baseline scan
Arrowheads = nerve
AA = axillary artery |
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B. In plane needle (arrows) approach
AA = axillary artery |
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C. Arrowheads = nerve structures; titling the needle tip (arrow) anteriorly shows that the needle tip is too superficial; needle tip is in the pectoralis minor muscle (PMiM).
AA = axillary artery |
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D. The needle tip (arrow) has now reached the posterior part of the axillary artery (AA, 6 o'clock position); tilting the needle at this point will slightly compress and displace the AA anteriorly.
AA = axillary artery |
2. Vertical Infraclavicular Block (Out of Plane Approach)
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The site of needle insertion for the VIB is approximately the mid point of the clavicle (CL). At this location, the brachial plexus is more superficial. The pleura and lung are usually 2-3 cm from the skin surface. |
Anatomical Correlation
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The brachial plexus (arrowheads) is commonly found lateral to the subclavian artery.
Arrowheads = nerves
PMM & PMiM = pectoralis major & minor muscles
SA & SV = subclavian artery & vein |
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Effect of arm abduction to enhance cord visualization
Arrowheads = nerves
SA & SV = subclavian artery & vein |
3. Vertical Infraclavicular Block (In Plane Approach)
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The brachial plexus can also be approached in plane with the needle pointing in a lateral to medial direction. |