Figure 1: In-plane needle insertion technique during infraclavicular brachial plexus block.
Indications: arm, elbow, forearm, and hand surgery
Transducer position: approximately parasagittal, just medial to coracoid process, inferior to clavicle
Goal: local anesthetic spread around axillary artery
Local anesthetic: 20-30 mL
Figure 2: Anatomy of the infraclavicular brachial plexus and the position of the transducer. Brachial plexus (BP) is seen surrounding the axillary artery (AA) underneath the clavicle (Cl) and pectoralis minor muscle (PMiM). Note that the injection of local anesthetic should take place below the fascia of the PMiM to spread around the AA. PMaM, pectoralis major muscle.
The ultrasound-guided infraclavicular brachial plexus block is in some ways both simple and challenging. It is simple in the sense that geometric measuring of distances and angles on the surface of the patient, as is the case with the nerve stimulator-based technique, is not required. Identification of the arterial pulse on the sonographic image is an easy primary goal in establishing the landmark. However, the plexus at this level is situated deeper, and the angle of approach is more acute, making simultaneous visualization of the needle and the relevant anatomy more challenging. Fortunately, although it is not always possible to reliably identify the three cords of the plexus at this position, adequate block can be achieved by simply depositing the local anesthetic in a U-shape around the artery. Infraclavicular block is well-suited for catheter technique because the musculature of the chest wall helps stabilize the catheter and prevents its dislodgment compared with the more superficial location with the interscalene or supraclavicular approaches.
The axillary artery can be identified deep to the pectoralis major and minor muscles. An effort needs to be made to obtain clear views of both pectoralis muscles and their respective fasciae. This is important because the area of interest lies underneath the fascia of the pectoralis minor muscle. Surrounding the artery are the three cords of the brachial plexus: the lateral, posterior, and medial cords. These are named for their usual position relative to the axillary artery, although there is a great deal of anatomic variation. With the left side of the screen corresponding to the cephalad aspect, the cords can often be seen as round hyperechoic structures at approximately 9 o’clock (lateral cord), 7 o’clock (posterior cord), and 5 o’clock (medial cord) (Figures 2, 3, and 4). The axillary vein is seen as a compressible hypoechoic structure that lies inferior, or slightly superficial, to the axillary artery. Multiple other, smaller vessels (e.g., the cephalic vein) are often present as well. The transducer is moved in the superior-inferior direction until the artery is identified in cross-section. Depending on the depth of field selected and the level at which the scanning is performed, the chest wall and lung may be seen in the inferior aspect of the image. The axillary artery and/or brachial plexus are typically identified at a depth of 3 to 5 cm in average size patients.
Distribution of Blockade
The infraclavicular approach to brachial plexus blockade results in anesthesia of the upper limb below the shoulder. The medial skin of the upper arm (intercostobrachial nerve, T2), if required, can be blocked by an additional subcutaneous injection on the medial aspect of the arm just distal to the axilla. A simpler approach is for surgeons to infiltrate the skin with the local anesthetic directly over the incision line, if necessary.
Equipment needed includes the following:
Ultrasound machine with linear transducer (8-14 MHz), sterile sleeve, and gel
Standard nerve block tray
20 to 30 mL of local anesthetic drawn up in syringes
8- to 10-cm long, 21-22 gauge short-bevel insulated stimulating needle
Peripheral nerve stimulator
Landmarks and Patient Positioning
Figure 5: Patient position in needle insertion for infraclavicular brachial plexus block. The transducer is positioned parasagittally just medial to the coracoid process and inferior to the clavicle.
Any position that allows comfortable placement of the ultrasound transducer and needle advancement is appropriate. The block is typically performed with the patient in supine position with the head turned away from the side to be blocked (Figure 5). The arm is abducted to 90° and the elbow flexed. This maneuver reduces the depth from the skin to the plexus and substantially facilitates visualization of the pectoralis muscles as well as the cords of the brachial plexus.
The coracoid process is an important landmark and can be easily identified by palpating the bony prominence just medial to the shoulder while the arm is elevated and lowered. As the arm is lowered, the coracoid process meets the fingers of the palpating hand. Scanning is usually begun just medial to the coracoid process and inferior to the clavicle. As scanning experience increases, it eventually becomes unnecessary to identify the coracoids process before scanning.
With the patient in the proper position, the skin is disinfected and the transducer is positioned in the parasagittal plane to identify the axillary artery (Figures 3 and 4, and 5). This may require adjustment of the depth, depending on the thickness of the patient’s chest wall musculature. The axillary artery (or the transition of the subclavian to axillary artery) is typically seen between 3 and 5 cm. Once the artery is identified, an attempt is made to identify the hyperechoic cords of the brachial plexus and their corresponding positions relative to the artery, although these may not always be identifiable. Fortunately, exhaustive efforts to visualize the cords are not necessary for successful blockade. The needle is inserted in-plane from the cephalad aspect, with the insertion point just inferior to the clavicle (Figure 5).
The needle is aimed toward the posterior aspect of the axillary artery and passes through the pectoralis major and minor muscles. If nerve stimulation is used concurrently (0.5-0.8 mA, 0.1 msec), the first motor response is often from the lateral cord (either elbow flexion or finger flexion). As the needle is further advanced beneath the artery, a posterior cord motor response may appear (finger and wrist extension). After careful aspiration, 1 to 2 mL of local anesthetic is injected to confirm the proper needle placement and spread. The injectate should spread cephalad and caudad to cover the lateral and medial cords, respectively (Figure 6). When injection of the local anesthetic with a single injection does not appear to result in adequate spread, additional needle repositions and injections around the axillary artery may be necessary (Figure 7).
In an adult patient, 20 to 30 mL of local anesthetic is usually adequate for successful blockade. Although a single injection of such large volumes of local anesthetic often suffices, it may be beneficial to inject two to three smaller aliquots at different locations to assure spread of the local anesthetic solution in all planes containing brachial plexus.
Continuous Ultrasound-Guided Infraclavicular Block
The goal of the continuous infraclavicular block is similar to the non-ultrasound-based techniques: to place the catheter in the vicinity of the cords of the brachial plexus beneath the pectoral muscles. The procedure consists of three phases: needle placement, catheter advancement, and securing of the catheter. For the first two phases of the procedure, ultrasound can be used to assure accuracy in most patients. The needle is typically inserted in-plane from the cephalad-to-caudad direction, similar to the single-injection technique (Figure 8).
Figure 8: Patient position, imaging and needle placement for continuous infraclavicular brachial plexus block are similar to those in a single-injection technique. Once the proper needle tip is determined by injection of a small volume of local anesthetic, the catheter is inserted 2-4 cm beyond the needle tip.
As with the single injection technique, the needle tip should be placed posterior to the axillary artery prior to injection and catheter advancement. Proper placement of the needle can also be confirmed by obtaining a motor response of the posterior cord (finger or wrist flexion) at which point 1 to 2 mL of local anesthetic is injected. This small dose of local anesthetic serves to document the proper placement of the needle tip as evidenced by adequate distribution of the local anesthetic. The injection also may make the advancement of the catheter more comfortable to the patient. This first phase of the procedure does not significantly differ from the single-injection technique. The second phase of the procedure involves maintaining the needle in the proper position and advancing the catheter 2 to 4 cm beyond the needle tip, in the vicinity of the posterior cord. Insertion of the catheter can be accomplished by either single operator or a with a helper (Figure 8). A typical starting infusion regimen is 5 mL/hour with 8-mL patient-controlled boluses every hour. The larger bolus volume is necessary for the adequate spread of the injectate around the artery to reach all cords of the brachial plexus. The catheter is secured by either taping to the skin or tunneling. Some clinicians prefer one over the other. However, the decision on which method to use could be based on the patient’s age, duration of the catheter therapy, and anatomy. Tunneling could be preferred in older patients with obesity or mobile skin over the neck and longer planned duration of the catheter infusion. One advantage to catheter placement with the infraclavicular approach is that the pectoralis muscles tend to stabilize the catheter and prevent dislodgment.