The neural innervations of the upper extremity provide unique opportunities for a wide selection of neural blockade options that can be tailored to the desired outcome needed for anesthesia or analgesia of the extremity.

The brachial plexus traverses the posterior triangle of the neck and the axilla. It provides complete innervation to the upper extremity. Proximally, the brachial plexus originates from the ventral primary rami of the cervical spinal nerves (C5–T1) (Figs. 2–1 and 2–2) and extends from the cervical spinal roots in the neck to its terminal nerves in the axilla (Fig. 2–3). The C5 and C6 rami unite to form the superior trunk, the C7 rami forms the middle trunk, and the C8 and T1 rami unite to form the inferior trunk (Fig. 2–4). The trunks of the brachial plexus are located in the interscalene groove between the scalenus anterior and the scalenus medius muscles, at the level of the cricoid cartilage (approximate C6 vertebral body level) and deep to the sternocleidomastoid muscle (Fig. 2–5). The anterior tubercle of the C6 vertebra is the most prominent of all the vertebrae (Chassaignac’s tubercle), and the C7 transverse process lacks the anterior tubercle. This feature can be used to sonographically identify the C7 nerve root. At the root level, the plexus gives off the dorsal scapular nerve and the long thoracic nerve (Fig. 2–4).

At the supraclavicular fossa, the trunks of the brachial plexus are superficial and divide into their anterior and posterior divisions and reunite as the cords distal to the clavicle. The trunks and divisions lie above the first rib between the scalenus anterior and scalenus medius muscles (Fig. 2–6). The subclavian artery crosses over the top of the first rib at this point as it exits the thoracic inlet and travels in the fascial plane between the scalenus anterior and the scalenus medius and is anteromedial to the trunks and divisions of the brachial plexus at this level (Fig. 2–6). The subclavian vein crosses the first rib lying anteriorly to the insertion of the scalenus anterior (Fig. 2–7). The pleura lies immediately deep to the first rib. At the trunk level, the plexus gives off the nerve to the subclavius and suprascapular nerve.

Lateral to the first rib the six divisions of the brachial plexus regroup to form the three cords of the brachial plexus. The posterior cord is formed from the three posterior divisions (C5–C8 and T1), the lateral cord from the anterior division of the upper and middle trunk (C5–C7), and the medial cord is a continuation of the anterior division of the lower trunk (C8 and T1). The cords then enters the “costoclavicular space” (CCS, Fig. 2–8), which is located deep and posterior to the middle-third of the clavicle. ^1,2 Within the CCS the cords are clustered together lateral to the axillary artery and between the clavicular head of the pectoralis major muscle and the subclavius muscle anteriorly, and the serratus muscle overlying the second rib posteriorly (Figs. 2–8 and 2–9). ^1,2 The topography of the cords relative to the axillary artery and to one another is consistent at the CCS (Figs. 2–9 to 2–11). The lateral cord is the most superficial of the three cords and always lies anterior to both the medial and posterior cords (Figs. 2–9 to 2–11). ³ The medial cord is directly posterior to the lateral cord but medial to the posterior cord (Fig. 2–9 to 2–11). ³ The posterior cord is the most lateral of the three cords at the CCS, and it is immediately lateral to the medial cord but posterolateral to the lateral cord (Figs. 2–9 to 2–11). ³ The cords then descend to the lateral infraclavicular fossa, deep to the pectoralis minor muscle, where they occupy their respective position relative to the second part of the axillary artery (Fig. 2–12). The posterior cord is located posterior to the artery, the lateral cord lies in the superolateral aspect of the artery, and the medial cord lies in the inferomedial aspect of the artery. ⁴ Position of the cords at the lateral infraclavicular fossa is variable ⁴ and affected by the position (abduction) of the arm. ⁵ The lateral cord gives off the lateral pectoral nerve, musculocutaneous nerve and lateral root of median nerve; the posterior cord gives off the upper and lower subscapular nerves, the thoracodorsal nerve, radial nerve, and axillary nerve; the medial cord gives off the medial pectoral nerve, the medial cutaneous nerve of the arm, medial cutaneous nerve of the forearm, ulnar nerve, and medial root of the median nerve.

The main terminal branches of the brachial plexus—median, radial, ulnar, and musculocutaneous nerve—leave the axilla with the axillary artery (Fig. 2–13) and continue their course into the arm (Fig. 2–14). At the anterior axillary fold, the musculocutaneous nerve leaves the brachial plexus and travels between the biceps brachii and the coracobrachialis in the proximal arm and subsequently between the biceps brachii and the brachialis in the midarm. Just before the cubital fossa, it emerges on the lateral border of the biceps tendon and pierces the deep fascia to become superficial and continue its course down the lateral aspect of the forearm as the lateral cutaneous nerve of the forearm.

Gross Anatomy

In the posterior triangle, the roots and trunks of the brachial plexus lie between scalenus anterior and medius muscles (Figs. 2–15 and 2–16). As the cervical nerve root (C3–C6) exits from the intervertebral foramen, it travels between the anterior and posterior tubercle of the corresponding cervical vertebra (Figs. 2–17 and 2–18). This unique feature can be easily demonstrated using ultrasound. Deep to the cervical nerve root, the vertebral artery travels in the foramen transversarium (Fig. 2–17) of the C6 to C1 vertebrae and ascends cranially.

Computed Tomography Anatomy of the Neck and Interscalene Region

Figs. 2–19 and 2–20

Magnetic Resonance Imaging Anatomy of the Neck and Interscalene Region

Figs. 2–21 and 2–22

Technique of Ultrasound Imaging of the Brachial Plexus at the Interscalene Groove

1. 
   

   Position:

   
   
   
   
   1. 
      

      Patient: Supine or semisitting position with head turned to the contralateral side (Fig. 2–23). The head rests on a low pillow with the arm adducted by the side.

      
      
   2. 
      

      Operator and ultrasound machine: Operator is positioned at the head end of the patient. The ultrasound machine is placed ipsilateral to the side examined and directly in front. The position of the operator and ultrasound machine can be easily reversed for convenience or, for example, to allow a right-handed operator to perform an ultrasound-guided interscalene brachial plexus block on the left side using his or her right hand.

   
   
   
   
2. 
   

   Transducer selection: High-frequency (15-8 or 17-5 MHz) linear array transducer.

   
   
3. 
   

   Scan technique: As part of a scan routine, it is advisable to start the ultrasound scan of the neck by placing the transducer in the midline (Fig. 2–24) at the level of the cricoid cartilage (C6). Place the transducer in a transverse orientation to image the cricoid cartilage (Fig. 2–25) or trachea (Fig. 2–26) in cross-section. Slide the transducer laterally to the side of interest, and identify the sternocleidomastoid muscle, trachea, thyroid, carotid artery, and internal jugular vein. Continue to manipulate the transducer laterally in the transverse plane to the lateral edge of the sternocleidomastoid muscle. The scalenus anterior and scalenus medius with the interscalene groove are located deep to the lateral edge of the sternocleidomastoid muscle (Figs. 2–27 and 2–28). Alternatively one can perform a transverse scan of the subclavian artery at the supraclavicular fossa (see later). The trunks and divisions of the brachial plexus are seen as a cluster of hypoechoic and rounded nodules on the posterolateral aspect of the subclavian artery, like a “bunch of grapes,” and between the scalenus anterior and scalenus medius muscles. Now slowly slide the transducer cephalad with a sweeping action when the roots and/or trunks of the brachial plexus are clearly delineated in the interscalene groove.

   
   
4. 
   

   Sonoanatomy: At the interscalene groove, the trunks of the brachial plexus are located between the scalenus anterior and the scalenus medius muscles (Fig. 2–29). They appear round to oval in shape, are hypoechoic in appearance, and may have a hyperechoic rim (Fig. 2–30). ⁶ The carotid artery and internal jugular vein are visualized medially, and the vertebral artery can also be seen adjacent to the C7 transverse process deep to the interscalene groove (Fig. 2–29).

   
   
5. 
   

   Clinical Pearls: The trunks of the brachial plexus are best visualized within the interscalene groove just below the level of the cricoid cartilage. They appear as three hypoechoic round-to-oval shaped structures, which produce a sonographic pattern resembling “traffic signal lights.” If one traces these neural elements medially and proximally to their intervertebral foramen, each of the cervical nerve roots can be identified as they lie anterior to the corresponding transverse processes. The roots of the brachial plexus are best visualized at the C6 (Fig. 2–31) or C7 (Fig. 2–32) vertebral level. The C6 transverse process is distinctive, as it is the first cervical vertebra counting from below, which has two tubercles (anterior and posterior, Fig. 2–31) on the transverse process. C3 to C6 cervical vertebrae have both the anterior and posterior tubercle on the transverse process. The C7 transverse process has only one tubercle (the anterior tubercle is rudimentary or absent), and this is typically posterior to the nerve root (Fig. 2–32). As a result of the two tubercles, the transverse processes of the lower cervical vertebrae (C3–C6) produce a “U” shaped or “fish mouth” pattern on the sonogram (Fig. 2–31). The resultant sonographic pattern has also been referred to as the “two-humped camel” sign. ⁷ The corresponding nerve roots can be visualized, coursing within the groove formed by the anterior and posterior tubercle just before they enter the neural foramen, by sliding the transducer proximally and distally. During the sliding maneuver, the vertebral artery can be visualized in the space between two adjacent transverse processes (intertransverse space). This can be confirmed using Color or Power Doppler. The vertebral artery is best visualized at the C7 vertebral level because of the absence of the anterior tubercle on the transverse process (Fig. 2–32). Alternatively the vertebral artery can be visualized by performing a sagittal scan at the level of transverse process through the intertransverse space (Fig. 2–33). The phrenic nerve may be seen on the anterior surface of the scalenus anterior (Figs. 2–29 and 2–30) as a small hypoechoic structure, and its identity can be confirmed by tracing the nerve proximally and distally along its course, ⁸ also referred to as the “trace back technique.” ⁹ It is also common to visualize vascular structures at the base of the posterior triangle of the neck. These may be the inferior thyroid artery, vertebral artery, suprascapular artery (see later), or the transverse cervical artery (Fig. 2–34). Verifying their course and origin allows one to confirm the identity of the artery. The superficial cervical plexus may also be visualized as a small collection of hypoechoic nerves deep to or lateral to the sternocleidomastoid muscle.

Assessment of Diaphragm Excursions

Ultrasound imaging is a safe, simple, and accurate method of evaluating diaphragmatic function (excursion) in patients with diaphragmatic paresis or paralysis. ¹⁰ In regional anesthesia ultrasound imaging can be used to evaluate phrenic nerve involvement by assessing diaphragmatic excursion after an interscalene brachial plexus block. ¹¹ A 5-2 MHz curved array transducer is used, and a B-mode ultrasound scan is initially performed with the patient in the supine position. A transverse scan of the subcostal region is performed with the ultrasound transducer placed between the midclavicular and midaxillary line. The liver or spleen (on the left side) provides the acoustic window for the ultrasound scan. For optimal imaging the ultrasound transducer is also directed cranially, posteriorly, and medially to image the posterior third of the diaphragm. Once an optimal B-mode image is obtained, the M-mode function is activated, with the M-mode line passing through the diaphragm (Fig. 2–35). Resting or forced diaphragmatic excursion after the “sniff test” (rapid nasal inspiration with the mouth closed) can then be assessed.

Gross Anatomy

At the supraclavicular fossa, the brachial plexus is relatively superficial and lies beneath the subcutaneous tissue and the inferior belly of the omohyoid. The trunks and division of the brachial plexus are seen as a cluster of nerves on the posterolateral aspect (Figs. 2–6, 2–7, 2–15, and 2–36) of the subclavian artery (Figs. 2–4 to 2–7). The subclavian artery lies on top of the first rib (Fig. 2–36), and the subclavian vein is anterior to the scalenus anterior muscle (Figs. 2–6 and 2–7).

Computed Tomography Anatomy of the Supraclavicular Fossa

Fig. 2–37

Magnetic Resonance Imaging Anatomy of the Supraclavicular Fossa

Fig. 2–38

Technique of Ultrasound Imaging of the Brachial Plexus at the Supraclavicular Fossa

1. 
   

   Position:

   
   
   
   
   1. 
      

      Patient: Supine position with head turned to the contralateral side. Position the head on a low pillow with the arm adducted by the side. A small roll or jelly pad placed under the shoulder may be helpful, as it increases the distance between the bed and the transducer. This facilitates needle placement and manipulation during an in-plane approach for supraclavicular brachial plexus block.

      
      
   2. 
      

      Operator and ultrasound machine: The operator sits or stands at the head end of the patient. The ultrasound machine is placed ipsilateral to the side to be examined and directly in front of the operator.

   
   
   
   
2. 
   

   Transducer selection: High-frequency (15-8 or 17-5 MHz) linear array transducer.

   
   
3. 
   

   Scan technique: The transducer is placed parallel to the clavicle in the supraclavicular fossa (Fig. 2–39). The ultrasound beam is directed towards the first rib and thoracic inlet (Fig. 2–40). The first reference structure to locate is the subclavian artery as it crosses the first rib.

   
   
4. 
   

   Sonoanatomy: At the supraclavicular fossa the trunks and divisions of the brachial plexus appear as a cluster of hypoechoic nodules, ¹² each with a hyperechoic rim (Fig. 2–41). Collectively, they appear as a “bunch of grapes” on the posterolateral aspect of the subclavian artery. Variations in this relationship have been described with the brachial plexus located farther laterally in relation to the subclavian artery. ¹³ The subclavian artery is pulsatile, can be demonstrated using Color Doppler, and is seen on top of the first rib. The first rib appears hyperechoic and is associated with an acoustic shadow (Fig. 2–41). The pleura is hyperechoic, deep to or on either side of the first rib, and exhibits the typical “lung sliding” sign. ¹⁴

   
   
5. 
   

   Clinical Pearls: With the transducer placed as described earlier and the subclavian artery visualized, optimization of the image to best visualize the brachial plexus is achieved with the tilting maneuver. The subclavian vein can often be seen lying on top of the pleura medially. It is also common to visualize one or more small arteries in this area. These are the suprascapular artery (Fig. 2–42) and the transverse cervical artery (Figs. 2–6 and 2–34). ¹⁵

Gross Anatomy

The infraclavicular fossa can be divided into two main areas: (1) the medial infraclavicular fossa (MICF), which extends from the lateral border of the first rib cranially to the superior (medial) border of the pectoralis minor muscle inferiorly, and (2) the lateral infraclavicular fossa (LICF), which lies deep to the pectoral muscles and in relation to the second part of the axillary artery. At the MICF, the cords of the brachial plexus emerge from under the clavicle and enter the CCS lying deep to the pectoralis major (clavicular head) and subclavius muscle anteriorly and the upper slips of the serratus anterior muscles posteriorly (Figs. 2–8 and 2–9). The cords of the plexus are clustered together lateral to the first part of the axillary artery (Figs. 2–9 to 2–11). ^1–3 This anatomical arrangement of the cords at the CCS makes it a suitable site for brachial plexus block (costoclavicular BPB). ² Very few BPB techniques have been described at the medial infraclavicular fossa. ^16,17 This may be due to the close proximity of the pleura to the plexus and the fear of inadvertent pleural or pulmonary puncture. As the plexus descends laterally towards the axilla, the cords of the brachial plexus are closely related to the second part of the axillary artery. They lie deep to the pectoralis major and minor muscles and anterior to the subscapularis muscle (Fig. 2–43). At the paracoracoid location or LICF, the cords of the brachial plexus have taken up their respective position around the axillary artery (Figs. 2–43 and 2–44). Generally, the lateral cord is superior, the posterior cord is posterior, and the medial cord is caudal to the axillary artery, respectively (Figs. 2–12 and 2–43). The position of the individual cords of the plexus can vary with the position of the arm (abduction or adduction). ⁵ Also the pleura and lung are not part of the posterior relation of the brachial plexus at the LICF (Fig. 2–44). Therefore it is a popular site for infraclavicular BPB, ¹⁸ as pleural puncture is thought to be unlikely. However, inadvertent pleural puncture has been reported, ¹⁹ which may be due to the block needle being inserted more medially than intended ¹⁹ when the pleura and lung are posterior to the axillary artery and brachial plexus (Fig. 2–44). Pleural complications should be avoidable with ultrasound guidance.

Computed Tomography Anatomy of the Infraclavicular Fossa

Figs. 2–45 to 2–48

Magnetic Resonance Imaging Anatomy of the Infraclavicular Fossa

Figs. 2–49 to 2–52

Technique of Ultrasound Imaging of the Brachial Plexus at the Medial Infraclavicular Fossa

1. 
   

   Position:

   
   
   
   
   1. 
      

      Patient: Supine with the ipsilateral arm abducted (90 degrees) and the head turned slightly to the contralateral side.

      
      
   2. 
      

      Operator and ultrasound machine: The operator is positioned at the head end of the patient. The ultrasound machine is placed on the ipsilateral side to be examined and directly in front.

   
   
   
   
2. 
   

   Transducer selection: High-frequency linear array transducer (12-5 or 15-8 MHz).

   
   
3. 
   

   Scan technique:

   
   
   
   
   1. 
      

      Transverse scan of the MICF: Transverse scan of the MICF is performed in five sequential steps, over five contiguous sites (Fig. 2–53). This is done to better define the anatomy of the CCS and the neighboring structures that are relevant for infraclavicular BPB.

      
      
      
      
      • 
        

        Step 1: The transducer is positioned directly over the midpoint of the clavicle in the transverse orientation (Fig. 2–54) with its orientation marker directed laterally (outwards). The clavicle is visualized as a curved hyperechoic structure with an underlying acoustic shadow (Fig. 2–55).

        
        
      • 
        

        Step 2: The transducer is gently moved caudally until it slips off the inferior border of the clavicle and the axillary artery (first part) and vein are visualized. It may be necessary to gently tilt the transducer cephalad to direct the ultrasound beam towards the CCS, that is, the space between the posterior surface of the clavicle and the second rib (Figs. 2–56 to 2–59). ^2,3 The ultrasound image is optimized until all three cords of the brachial plexus are clearly visualized lateral to the axillary artery (Figs. 2–56 and 2–58). If the ultrasound image is less than optimal, the medial end of the ultrasound transducer should be gently pivoted caudally to try and insonate the ultrasound beam at right angles to the cords and thus minimize anisotropy (Fig. 2–56).

        
        
      • 
        

        Step 3: The transducer is then gently manipulated laterally, maintaining the same transverse orientation and applying minimal pressure over the area scanned, until the cephalic vein is visualized (Figs. 2–60 and 2–61).

        
        
      • 
        

        Step 4: From this position the transducer is manipulated further laterally until the thoracoacromial artery (TAA) is seen to emerge from the axillary artery (second part) (Figs. 2–62 and 2–63).

        
        
      • 
        

        Step 5: The ultrasound transducer is manipulated further laterally to the LICF (Fig. 2–64).

      
      
      
      
   2. 
      

      Sagittal scan of the MICF: A sagittal scan of the MICF can be performed with the ultrasound transducer (a) at right angles to the midpoint of the clavicle (Figs. 2–65 to 2–67) or (b) with the ultrasound transducer parallel to (or in line with) the neurovascular structures (Figs. 2–68 to 2–70). From each of these positions the ultrasound transducer is gently manipulated laterally (ie, towards the shoulder) to view the related anatomy.

   
   
   
   
4. 
   

   Sonoanatomy of the MICF:

   
   
   
   
   1. 
      

      Transverse sonoanatomy of the MICF: On a transverse sonogram of the upper part of the MICF immediately below the midpoint of the clavicle (Step 2 of the transverse scan sequence), one can visualize the CCS between the clavicular head of the pectoralis major and subclavius muscle anteriorly and the serratus anterior muscle overlying the second rib posteriorly (Figs. 2–58 and 2–59). ^1,2 The first part of the axillary artery and the axillary vein appear as two hypoechoic round-to-oval structures within the CCS (Fig. 2–58). The axillary artery is pulsatile and located lateral to the axillary vein (Fig. 2–58). Deep to the axillary artery the upper slips of the serratus anterior muscle, second rib, intercostal muscles, and parietal pleura are clearly delineated (Fig. 2–59). The cords are clustered together lateral to the axillary artery, and they exhibit a consistent triangular topographical arrangement (Figs. 2–58 and 2–59). ^1,2 The lateral cord is the most superficial of the three cords and lies anterior to both the medial and posterior cords (Figs. 2–58 and 2–59). ³ The medial cord is directly posterior to the lateral cord but medial to the posterior cord (Fig. 2–58). ³ The posterior cord is the most lateral of the three cords at the CCS, and it is immediately lateral to the medial cord but posterolateral to the lateral cord (Figs. 2–58 and 2–59). ³ In the transverse sonogram immediately lateral to the CCS (Step 3 of the transverse scan sequence), the cephalic vein is seen arching over the axillary artery to join the axillary vein from a lateral to medial direction (Figs. 2–60 and 2–61). The cephalic vein is easily compressible with pressure from the transducer, but the axillary artery is more resistant to compression. The cords of the brachial plexus are seen as a hyperechoic cluster of nerves that lie deep to the cephalic vein and lateral to the axillary artery (Figs. 2–60 and 2–61). Because the cephalic vein lies anterior to the cords, this ultrasound window is not ideal for performing BPB because of the risk of puncturing the cephalic vein. Also if one does see the cephalic vein in the ultrasound window during a costoclavicular BPB, then it implies that the transducer is positioned lower than the desired location. If one now slides or tilts the transducer slightly laterally from the scan position described earlier (Step 4 of the transverse scan sequence), the cephalic vein is no longer visible and the TAA, which is a branch of the axillary artery, is visualized (Figs. 2–62 and 2–63). It is seen emerging from the anterior surface of the axillary artery and may be seen either as two arteries (Fig. 2–62) or as a single vessel lying deep and close to the upper border of the pectoralis minor muscle (Fig. 2–63). From this position gentle lateral manipulation of the transducer will reveal the LICF where the cords of the brachial plexus are closely related to the second part of the axillary artery (Fig. 2–64).

      
      
   2. 
      

      Sagittal sonoanatomy of the MICF: On a sagittal sonogram of the MICF, with the ultrasound transducer positioned at a right angle to the midpoint of the clavicle (Fig. 2–65), the cords of the brachial plexus are seen as multiple hypoechoic round to oval, structures each with a hyperechoic rim lying superior to the pulsatile axillary artery (Figs. 2–66 to 2–68). The cords lie within the CCS formed by the pectoralis major and subclavius muscle anteriorly and the upper slips of the serratus anterior muscle and chest wall posteriorly (Figs. 2–66 to 2–68). The axillary vein is located caudal to the axillary artery (Figs. 2–66 to 2–68), and the cephalic vein joins the axillary vein from above (Fig. 2–68). Deep to the serratus anterior muscle outlines of the anterior intercostal space and the hyperechoic pleura are clearly visualized. The arrangement of the cords in the sagittal sonogram is also consistent, ²⁰ with the lateral cord lying anterior to the medial cord, and the posterior cords lying superior to the medial and lateral cord (Figs. 2–66 to 2–68). ²⁰

      
      
      
      
      • 
        

        On a sagittal sonogram of the MICF, with the ultrasound transducer positioned parallel to the long axis of the neurovascular structures (Figs. 2–69 to 2–71) and from a medial to lateral direction, the axillary vein is the first structure visualized (Fig. 2–69). The axillary vein is hypoechoic, nonpulsatile, easily compressible, and lies on the anterior chest wall. The cephalic vein is also delineated and, after it traverses the gap between the clavicular head of the pectoralis major and the subclavius muscle, joins the axillary vein from above (Fig. 2–69). In the adjoining sagittal sonogram, the pulsatile axillary artery is visualized (Fig. 2–70). The axillary artery, after it emerges from the CCS, lies in the MICF, deep to the clavicular head of the pectoralis major muscle and above the superior border of the pectoralis minor muscle (Fig. 2–69). The cephalic vein lies anterior to the axillary artery at the MICF (Fig. 2–69). The axillary artery continues distally to enter the LICF, where it is located posterior to the pectoralis major and minor muscles (Fig. 2–70). The axillary artery also gives off the TAA from its anterior wall, and the latter ascends cranially, lying close to the posterior surface of the pectoralis minor muscle (Fig. 2–70). In the sagittal sonogram acquired immediately lateral and parallel to the axillary artery, the cords of the brachial plexus are visualized as longitudinal hyperechoic structures (Fig. 2–71) and lying within the CCS (close to the clavicle), MICF and LICF from a cranial to caudal direction (Fig. 2–71). At the MICF the cephalic vein and TAA (possibly the pectoral branch) lie anterior to the cords (Fig. 2–71). Due to the anatomic arrangement of the cords at the MICF (Figs. 2–10 and 2–11), all three cords of the brachial plexus are rarely visualized in a single sagittal sonogram. It is more common to visualize two cords, that is, the lateral cord lying anterior to the medial cord (Fig. 2–71).

      
      

   
   
   
   
5. 
   

   Clinical Pearls: The CCS may offer advantages for BPB, and ultrasound-guided costoclavicular BPB has recently been described. ² At the CCS, and in contrast to that at the LICF, the cords of the brachial plexus are relatively superficial (2–3 cm) in location, they are clustered together lateral to the axillary artery, ^1–3 and they share a consistent anatomical relationship with one another and to the axillary artery. ^1–3 All three cords of the brachial plexus are also visualized in a single transverse sonogram of the MICF. ² Therefore, it is possible to produce BPB at the CCS using a single injection of a relatively low volume (20 mL) of local anesthetic, ² unlike that at the LICF where multiple injections ²¹ and relatively large volumes of local anesthetics (up to 35 mL) are often required to produce an effective BPB. ^21,22 The CCS is also a useful site for catheter placement when a continuous BPB is planned for postoperative pain management, ² because the cords are close to one another. In our experience continuous BPB can be achieved via the CCS using very small volumes of local anesthetic for the infusion (eg, 4–5 mL/h of levobupivacaine 0.125%). However, currently there are limited published data on the safety and efficacy of BPB at the MICF. ^16,17 Overall, a medial approach may be desirable for BPB, but needle interventions at the MICF carry a definite risk of pleural puncture. Therefore, until more data on safety and efficacy are available, infraclavicular BPB techniques at the MICF should be considered an advanced technique and used with caution because the lateral sagittal infraclavicular BPB technique, despite some of its limitations, is effective and has a long track record of safety. ^18,23