31 Infraclavicular Block

Infraclavicular block of the brachial plexus was developed as a means to achieve complete brachial plexus anesthesia and was one of the first blocks to be described using ultrasound imaging.^1,² This block is performed at the level of the pectoralis minor muscle. In this location the brachial plexus consists of three cords that compactly hug the walls of the second part of the axillary artery.³ The infraclavicular region has the advantage of being a secure place for a catheter that provides complete brachial plexus anesthesia. Another advantage is that anatomic variation is relatively uncommon in this region. In the infraclavicular region, the serratus anterior and subscapularis muscles form the margin of safety between the neurovascular bundle and the chest. Because proximal arm muscles are anesthetized (including the pectoralis and deltoid), infraclavicular blocks produce excellent tourniquet tolerance and conditions for upper extremity surgery.⁴ The block can be performed with the arm abducted or at the patient’s side (Table 31-1).

Table 31-1 Clinical Considerations for Infraclavicular Block

Advantages	Disadvantages
Compact brachial plexus Anatomic variation uncommon Stable location for catheters Arm positioning Tourniquet tolerance	Deeper block Specialized equipment (small curved probe)

The major disadvantage of infraclavicular blocks is that the plexus is deep, with the neurovascular bundle being covered by both the pectoralis major and pectoralis minor muscles. Therefore, low-frequency, small, curved transducers are generally favored. Although the block can be performed with the arm at the side, it is still best to abduct the arm if possible to straighten the neurovascular bundle and retract the clavicle to provide more working room. Because the block is deep, an echogenic or large-bore needle is recommended (17 or 18 gauge) to improve needle tip visibility.

The three cords of the brachial plexus (medial, lateral, and posterior) are closely adherent to the second part of the axillary artery that lies beneath the pectoralis minor muscle. This arrangement of cords around the second part of the axillary artery is maintained across these spaces like a “three-point” star with the artery centered in the middle. The subscapularis muscle separates the infraclavicular brachial plexus from the lung, with a larger margin of safety laterally than medially. The pectoral nerves are sometimes visualized between the pectoralis major and pectoralis minor muscles.

Cord topography changes along the length of the axillary artery in the infraclavicular region.⁵ Proximally, the cords of the brachial plexus have more of a “supraclavicular” configuration in which all the cords are on the lateral side of the axillary artery. Following distally, the true “infraclavicular” configuration is when all cords surround the axillary artery before the takeoff of the axillary and musculocutaneous nerves. When the transducer is too proximal, the curved inclination of the ribs and pleura can be recognized. When the transducer is too distal, the coracobrachialis muscle and musculocutaneous nerve can be appreciated on the lateral side of artery.

The axillary vein lies on the medial (caudal) side of the axillary artery. Occasionally a duplicate axillary vein is observed. The cephalic vein enters the axillary vein from the lateral side by traveling through the deltopectoral groove. The cephalic vein can lie over the axillary artery in the infraclavicular region and can be recognized by its “tadpole” shape. Otherwise, there are few veins within the field of imaging for infraclavicular block.