FIGURE 29-1. Ultrasound-guided interscalene brachial plexus block; transducer and needle position to obtain the desired ultrasound image for an in-plane approach.
The ultrasound-guided technique of interscalene brachial plexus block differs from nerve stimulator or landmark-based techniques in several important aspects. Most importantly, distribution of the local anesthetic is visualized to assure adequate spread around the brachial plexus. Ultrasound guidance allows multiple injections around the brachial plexus, therefore eliminating the reliance on a single large injection of local anesthetic for block success as is the case with non–ultrasound-guided techniques. Ability to inject multiple aliquots of local anesthetic also may allow for the reduction in the volume of local anesthetic required to accomplish the block. Repetition of the block in case of inadequate anesthesia is also possible, a management option that is unpredictable without ultrasound guidance. Finally, the risk of major vessel and nerve puncture during nerve block performance is reduced.
The brachial plexus at the interscalene level is seen lateral to the carotid artery, between the anterior and middle scalene muscles (Figures 29-2, 29-3, and 29-4). Prevertebral fascia, superficial cervical plexus and sternocleidomastoid muscle are seen superficial to the plexus. The transducer is moved in the superior-inferior direction until two or more of the brachial plexus trunks are seen in the space between the scalene muscles. Depending on the depth of field selected and the level at which the scanning is performed, first rib and/or apex of the lung may be seen. The brachial plexus is typically visualized at a depth of 1 to 3 cm.
FIGURE 29-2. Relevant anatomy for interscalene brachial block and transducer position to obtain the desired views. Brachial plexus (BP) is seen sandwiched between middle scalene muscle (MSM) laterally and anterior scalene muscle (ASM) medially. Ultrasound image often includes a partial view of the lateral border of the sternocleidomastoid muscle (SCM) as well as the internal jugular vein (IJV) and carotid artery (CA). The transverse process of one of the cervical vertebrae is also often seen.
FIGURE 29-3. Interscalene brachial plexus is seen between middle scalene muscle and anterior scalene muscle. Carotid artery is seen medial at 1 cm depth in this image.
FIGURE 29-4. Typical image of the brachial plexus (BP). The BP is seen positioned between the anterior scalene muscle (ASM) and the middle scalene muscle (MSM). The superficial cervical plexus (white arrowhead) can be seen posterior to the SCM and underneath the prevertebral fascia. In this particular image, the vertebral artery (VA), carotid artery (CA), as well as the transverse process of C6 are also seen.
Distribution of Blockade
The interscalene approach to brachial plexus blockade results in anesthesia of the shoulder and upper arm. Inferior trunk for more distal anesthesia can also be blocked by additional, selective injection, deeper in the plexus. This is accomplished either by controlled needle redirection inferiorly or by additional scanning to visualize the inferior trunk and another needle insertion and targeted injection. For a more comprehensive review of the brachial plexus distribution, see Chapter 1 on Essential Regional Anesthesia Anatomy.
Equipment needed includes the following:
• Ultrasound machine with linear transducer (8–14 MHz), sterile sleeve, and gel
• Standard nerve block tray (described in the equipment section)
• One 20-mL syringe containing local anesthetic
• 5-cm, 22-gauge short-bevel insulated stimulating needle
• Peripheral nerve stimulator
• Sterile gloves
Landmarks and Patient Positioning
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, semisitting, or semilateral decubitus position, with the patient’s head facing away from the side to be blocked. The latter position may prove ergonomically more convenient, especially during an in-plane approach from the lateral side, in which the needle is entering the skin at the posterolateral aspect of the neck. A slight elevation of the head of the bed is often more comfortable for the patient, and it allows for better drainage and less prominence of the neck veins.
Adherence to strict anatomic landmarks is of lesser importance for the ultrasound-guided interscalene block than it is the case for the surface anatomy-based techniques. Regardless, knowledge of the underlying anatomy and the position of the brachial plexus is important to facilitate recognition of the ultrasound anatomy. Scanning usually begins just below the level of the cricoid cartilage and medial to the sternocleidomastoid muscle with a goal to identify the carotid artery.
The goal is to place the needle in the tissue space between the anterior and middle scalene muscles and inject local anesthetic until the spread around the brachial plexus is documented by ultrasound. The volume of the local anesthetic and number of needle insertions are determined during the procedure and depend on the adequacy of the observed spread of the local anesthetic.
With the patient in the proper position, the skin is disinfected and the transducer is positioned in the transverse plane to identify the carotid artery (Figure 29-5). Once the artery is identified, the transducer is moved slightly laterally across the neck (see algorithm at end of chapter). The goal is to identify the scalene muscles and the brachial plexus that is sandwiched between the anterior and middle scalene muscles.
FIGURE 29-5. Ultrasound image just below the level of the cricoid cartilage and medial to the sternocleidomastoid muscle. ASM, anterior scalene muscle; SCM, sternocleidomastoid muscle; IJV, internal jugular vein; CA, carotid artery; Th, thyroid gland.
• When the visualization of the brachial plexus between the scalene muscles proves difficult, the transducer is lowered to the supraclavicular fossa. At this position, the brachial plexus is identified lateral and superficial to the subclavian artery, (Figure 29-6). From here, the brachial plexus is traced cranially to the desired level.
FIGURE 29-6. View of the brachial plexus (BP) at the supraclavicular fossa. When identification of the brachial plexus at the interscalene level proves difficult, the transducer is positioned at the supraclavicular fossa to identify the BP superficial and lateral to the subclavian artery (SA). The transducer is then slowly moved cephalad while continuously visualizing the brachial plexus until the desired level is reached.
The needle is then inserted in-plane toward the brachial plexus, typically in a lateral-to-medial direction (Figure 29-7), although medial-to-lateral needle orientation also can be chosen if more convenient. As the needle passes through the prevertebral fascia, a certain “give” is often appreciated. When nerve stimulation is used (0.5 mA, 0.1 msec), the entrance of the needle in the interscalene groove is often associated with a motor response of the shoulder, arm, or forearm as another confirmation of the proper needle placement. After a careful aspiration to rule out an intravascular needle placement, 1 to 2 mL of local anesthetic is injected to document the proper needle placement (Figure 29-8A). Injection of several milliliters of local anesthetic often displaces the brachial plexus away from the needle. An additional advancement of the needle 1 to 2 mm toward the brachial plexus may be beneficial to assure a proper spread of the local anesthetic (Figure 29-8B). Whenever the needle is further advanced, or multiple injections used, assure that high resistance to injection is absent to decrease the risk of an intrafascicular injection. When injection of the local anesthetic does not appear to result in a spread around the brachial plexus, additional needle repositions and injections may be necessary.
FIGURE 29-7. (A) Transducer placement and needle insertion. (B) Position of the needle (1) for the interscalene brachial plexus block using an in-plane approach. The needle tip is seen in contact with the superior trunk of the brachial plexus (yellow arrows); this always results in high injection pressure (>15 psi)—indicating that the needle should be withdrawn slightly away from the trunk.
FIGURE 29-8. (A) A small amount of local anesthetic (blue shaded area) is injected through the needle to confirm the proper needle placement. A properly placed needle tip will result in distribution of the local anesthetic between and/or alongside roots of the brachial plexus (BP). (B) An actual needle (white arrowhead) placement in the interscalene groove with the dispersion of the local anesthetic (LA; blue shaded area or arrows) surrounding the BP.
• The presence of the motor response to nerve stimulation is useful but not necessary to elicit if the plexus, needle, and local anesthetic spread are well-visualized.
• The neck is a very vascular area, and care must be exercised to avoid needle placement or injection into the vascular structures. Of particular importance is to avoid the vertebral artery, and branches of the thyrocervical trunk: inferior thyroid artery, suprascapular artery, and transverse cervical artery.
• Never inject against high resistance (>15 psi) because this may indicate a needle-nerve contact or an intrafascicular injection.
• Pro and con of multiple injections:
Pro: May increase the speed of onset and success rate of the interscalene block.
Pro: May allow for a reduction in the total volume and dose of local anesthetic required to accomplish block.
Con: May carry a higher risk of nerve injury because part of the plexus may be anesthetized by the time consecutive injections are made.
NOTE: Avoidance of high resistance to injection and needle–nerve contact is essential to avoid intrafascicular injection because reliance on nerve stimulation with multiple injections is diminished.
In an adult patient, 15 to 25 mL of local anesthetic is usually adequate for successful and rapid onset of blockade. Smaller volumes of local anesthetics can also be effective, however, their success rate in everyday clinical practice may be inferior to those reported in meticulously conducted clinical trials. The block dynamics and perioperative management are similar to those described in Chapter 12.
Continuous Ultrasound-Guided Interscalene Block
The goal of the continuous interscalene block is similar to the non–ultrasound-based techniques: to place the catheter in the vicinity of the trunks of the brachial plexus between the scalene 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. The needle is typically inserted in-plane from the lateral-to-medial direction and underneath the prevertebral fascia to enter the interscalene space (Figure 29-9), although other needle directions could be used.
FIGURE 29-9. Continuous brachial plexus block. Needle is inserted in the interscalene space using an in-plane approach. Please note that for better demonstration, sterile drapes are not used in the model in this figure.
• Both stimulating and nonstimulating catheters can be used, although for simplicity we prefer nonstimulating catheters for ultrasound-guided continuous interscalene block.
Proper placement of the needle can also be confirmed by obtaining a motor response of the deltoid muscle, arm, or forearm (0.5 mA, 0.1 msec) at which point 4 to 5 mL of local anesthetic can be injected. This small dose of local anesthetic serves to assure adequate distribution of the local anesthetic as well as to 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 inserting the catheter 2 to 3 cm into the interscalene space in the vicinity of the brachial plexus (Figure 29-10). Insertion of the catheter can be accomplished by a single operator or with a helper. Proper location of the catheter can be determined either by visualizing the course of the catheter or by an injection of the local anesthetic through the catheter. When this proves difficult, alternatively, a small amount of air (1 mL) can be injected to confirm the catheter tip location.
FIGURE 29-10. An ultrasound image demonstrating needle and catheter (white arrow) inserted in the interscalene space between the anterior (ASM) and middle (MSM) scalene muscles. BP, brachial plexus.
There is no agreement on what constitutes the ideal catheter securing system. The catheter is secured by either taping to the skin or tunneling. Some clinicians prefer one over the other. However, the decision about 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 when longer duration of catheter infusion is expected. Two main disadvantages of tunneling are the risk of catheter dislodgment during the tunneling and the potential for scar formation. Fortunately, a number of catheter-securing devices are available to help stabilize the catheter.
Single Injection UG-IS block
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Continuous US-IS Block
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