Regional anesthetic approaches to the brachial plexus are a mainstay of surgical anesthesia practice and play an increasingly important role in postoperative analgesia. Well-designed outcome studies have confirmed the benefits of regional anesthesia in patients undergoing upper extremity surgery. When compared with traditional opioid-based postoperative analgesia for outpatient shoulder, arm, or hand surgery, single-injection regional anesthesia techniques provide superior analgesia, reduce opioid-related side effects, improve patient satisfaction, and reduce the number of unplanned admissions. Although these benefits are generally limited to the day of surgery, they nevertheless represent a valuable alternative to general anesthetic and postoperative opioid techniques. Furthermore, limited comparative studies have shown that an interscalene or suprascapular block provides better analgesia than does an intra-articular injection or infusion of local anesthetic and without any risk for chondrolysis. Continuous perineural catheter techniques provide superior analgesia for total shoulder arthroplasty and various ambulatory shoulder surgeries. Similar to single-injection techniques, the prolonged analgesia afforded by continuous perineural catheters is associated with fewer opioid-related side effects and higher patient satisfaction. What remains unclear is whether these techniques substantially improve economic outcomes such as faster rehabilitation or return to work. This chapter offers a brief review of brachial plexus anatomy and pertinent pharmacology, with a primary focus on the techniques and complications of upper extremity blocks.
Brachial Plexus Anatomy
The brachial plexus is composed of the ventral primary rami of cervical nerves C5 to C8 and thoracic nerve T1, with occasional contributions from C4 and T2 ( Fig. 53.1 ). Understanding the complex interdigitations that define the brachial plexus is important for two reasons. First, brachial plexus approaches are directed toward its various anatomic divisions. For example, the interscalene approach is directed toward the level of the distal roots and proximal trunks, whereas the infraclavicular approach is directed toward the level of the cords. This anatomic subarchitecture, in turn, determines the expected motor response to peripheral nerve stimulation and the distribution of anesthetic resulting from the particular approach. Second, supplemental procedures are often necessary to anesthetize nerves that are distinct from the brachial plexus or are intermediary branches. For example, the intercostobrachial nerve is primarily derived from T2, which is not part of the brachial plexus and must therefore be blocked separately if anesthesia of the medial aspect of the upper part of the arm is desired. Therefore, basic knowledge of brachial plexus anatomy is crucial for understanding the advantages and limitations of the various approaches to upper extremity regional anesthesia.
The functional neuroanatomy of the upper extremity is critically important for determining selection of the block and assessment. Motor function is generally well correlated with an observed motor response after electrical stimulation of a specific terminal nerve; for example, distal stimulation of the radial nerve consistently elicits wrist and finger extension. In contrast, as one moves proximally along the brachial plexus, stimulation yields muscle movements of a mixed nature. As an example of this concept, electrical stimulation of the superior trunk during the interscalene approach results in mixed muscle stimulation that produces shoulder elevation ( Table 53.1 ).
| Approach | Stimulated Portion of the Brachial Plexus | Expected Motor Response |
|---|---|---|
| Interscalene | Superior trunk | Shoulder abduction, elbow flexion |
| Supraclavicular | Middle and inferior trunk | Hand movement |
| Infraclavicular | Lateral cord | Forearm flexion, hand pronation (the little finger moves laterally) |
| Posterior cord | Wrist extension (the little finger moves posteriorly) | |
| Medial cord | Finger flexion, thumb opposition (the little finger moves medially) | |
| Axillary | Musculocutaneous nerve | Forearm flexion, hand supination |
| Median nerve | Forearm pronation, wrist flexion | |
| Ulnar nerve | Finger flexion, thumb opposition | |
| Radial nerve | Wrist extension |
Sensory innervation of the upper extremity is inconsistent and widely overlapping ( Fig. 53.2 ). Certain areas of the arm, such as the distal palmar aspect of the forearm, have overlapping sensory innervation from the medial and lateral antebrachial cutaneous nerves, plus occasional contributions from the median nerve. A practical implication of this neuroanatomic overlap is that most areas of the upper extremity require anesthesia of two or more terminal nerves, which supports the effectiveness of plexus-based regional anesthesia over multiple selective nerve blocks at the elbow or wrist. Furthermore, overlapping cutaneous sensory fields and motor function can be problematic for assessing anesthesia, which is best accomplished by testing end functions that can be attributed only to a single nerve. The “four P’s” is an example of such a tool ( Table 53.2 ).
| P | Action | Nerve Assessed |
|---|---|---|
| Push | Extend the forearm against resistance | Radial |
| Pull | Flex the forearm against resistance | Musculocutaneous |
| Pinch | Pinch the palmar base of the index finger | Median |
| Pinch | Pinch the palmar base of the little finger | Ulnar |
Pharmacologic Considerations
Selection of a local anesthetic for brachial plexus anesthesia is based on the expected duration of surgery and the optimal duration of postoperative analgesia. When considering block duration, anesthesiologists should be cognizant of the expected degree of postoperative pain. For mildly painful procedures, some patients may interpret prolonged arm numbness as bothersome, whereas dense analgesia may mask early signs of impaired circulation in crush injuries or surgeries with potential for the development of compartment syndrome. Thus, selection of a local anesthetic for an upper extremity block is best individualized to achieve specific therapeutic goals.
Potency studies of long-acting local anesthetics applied to the brachial plexus suggest that 0.5% bupivacaine is equipotent to 0.75% ropivacaine. This equivalence is important because a tendency to use more ropivacaine to attain the same effect as bupivacaine will probably negate the lower cardiotoxicity properties of ropivacaine. When considering the total mass (dose) of a local anesthetic, decisions are best skewed toward using a lower volume, concentration, and dose. Although it may appear counterintuitive, the work of Vester-Andersen and colleagues, along with other confirmatory investigations, clearly demonstrates that block onset, quality, and duration are not improved by using larger volumes or concentrations of local anesthetic. Indeed, doing so risks local anesthetic concentration-dependent neurotoxicity and dose-dependent systemic toxicity. Therefore, traditional local anesthetic volumes for an upper extremity plexus block are generally between 20 and 40 mL, depending on the approach chosen, and concentrations to produce surgical anesthesia should be 1.5% or less for lidocaine or mepivacaine, 0.75% or less for ropivacaine, and 0.5% or less for bupivacaine. Conversely, if one seeks only postoperative analgesia, ultrasound guidance facilitates the use of much lower volumes of local anesthetic for an interscalene block. However, further evidence suggests that ultrasound-guided regional anesthesia (UGRA) with low-volume blocks may indeed result in a shorter duration of analgesia.
Four local anesthetic additives have proven value when applied to the brachial plexus. Epinephrine, 2.5 µg/mL (1:400,000), prolongs the duration, acts as a marker of intravascular injection, and decreases systemic uptake of local anesthetic. The ability of epinephrine to prolong a local anesthetic block is a consequence of reduced clearance from the injection site, and it is unlikely to involve a significant α 2 -adrenergic agonist effect. Epinephrine is unique among local anesthetic additives in that its associated tachycardia can serve as a marker of intravascular injection. Clonidine, 0.5 µg/kg, prolongs anesthesia and analgesia by 50% without systemic side effects such as hypotension or sedation. Clonidine does not improve block quality during continuous perineural catheter techniques. The effect of epinephrine and clonidine on intermediate-acting local anesthetics is clinically significant, but they do not reliably prolong the duration of long-acting local anesthetics. Buprenorphine, 0.3 mg, also prolongs anesthesia and analgesia, but at the expense of nausea and vomiting. Dexamethasone can also prolong intermediate-acting agents to a degree similar to epinephrine, but the optimal dose and any potential long-term effects of dexamethasone remain uncertain. The beneficial effects of these additives, as well as their potential neurotoxicity, alone and in combination, are currently still under investigation. Other opioids, neostigmine, calcium channel blockers, hyaluronidase, and tramadol either do not improve local anesthetic blocks or have unresolved neurotoxicity issues.
Alkalinization of intermediate-acting local anesthetics facilitates faster onset of the block during epidural anesthesia but does not have the same effect at the brachial plexus. Onset is not hastened by adding sodium bicarbonate to plain local anesthetic or to local anesthetic freshly mixed with epinephrine. Indeed, animal models have shown that alkalinization of local anesthetic reduces block intensity and duration.
Pharmacologic Considerations
Selection of a local anesthetic for brachial plexus anesthesia is based on the expected duration of surgery and the optimal duration of postoperative analgesia. When considering block duration, anesthesiologists should be cognizant of the expected degree of postoperative pain. For mildly painful procedures, some patients may interpret prolonged arm numbness as bothersome, whereas dense analgesia may mask early signs of impaired circulation in crush injuries or surgeries with potential for the development of compartment syndrome. Thus, selection of a local anesthetic for an upper extremity block is best individualized to achieve specific therapeutic goals.
Potency studies of long-acting local anesthetics applied to the brachial plexus suggest that 0.5% bupivacaine is equipotent to 0.75% ropivacaine. This equivalence is important because a tendency to use more ropivacaine to attain the same effect as bupivacaine will probably negate the lower cardiotoxicity properties of ropivacaine. When considering the total mass (dose) of a local anesthetic, decisions are best skewed toward using a lower volume, concentration, and dose. Although it may appear counterintuitive, the work of Vester-Andersen and colleagues, along with other confirmatory investigations, clearly demonstrates that block onset, quality, and duration are not improved by using larger volumes or concentrations of local anesthetic. Indeed, doing so risks local anesthetic concentration-dependent neurotoxicity and dose-dependent systemic toxicity. Therefore, traditional local anesthetic volumes for an upper extremity plexus block are generally between 20 and 40 mL, depending on the approach chosen, and concentrations to produce surgical anesthesia should be 1.5% or less for lidocaine or mepivacaine, 0.75% or less for ropivacaine, and 0.5% or less for bupivacaine. Conversely, if one seeks only postoperative analgesia, ultrasound guidance facilitates the use of much lower volumes of local anesthetic for an interscalene block. However, further evidence suggests that ultrasound-guided regional anesthesia (UGRA) with low-volume blocks may indeed result in a shorter duration of analgesia.
Four local anesthetic additives have proven value when applied to the brachial plexus. Epinephrine, 2.5 µg/mL (1:400,000), prolongs the duration, acts as a marker of intravascular injection, and decreases systemic uptake of local anesthetic. The ability of epinephrine to prolong a local anesthetic block is a consequence of reduced clearance from the injection site, and it is unlikely to involve a significant α 2 -adrenergic agonist effect. Epinephrine is unique among local anesthetic additives in that its associated tachycardia can serve as a marker of intravascular injection. Clonidine, 0.5 µg/kg, prolongs anesthesia and analgesia by 50% without systemic side effects such as hypotension or sedation. Clonidine does not improve block quality during continuous perineural catheter techniques. The effect of epinephrine and clonidine on intermediate-acting local anesthetics is clinically significant, but they do not reliably prolong the duration of long-acting local anesthetics. Buprenorphine, 0.3 mg, also prolongs anesthesia and analgesia, but at the expense of nausea and vomiting. Dexamethasone can also prolong intermediate-acting agents to a degree similar to epinephrine, but the optimal dose and any potential long-term effects of dexamethasone remain uncertain. The beneficial effects of these additives, as well as their potential neurotoxicity, alone and in combination, are currently still under investigation. Other opioids, neostigmine, calcium channel blockers, hyaluronidase, and tramadol either do not improve local anesthetic blocks or have unresolved neurotoxicity issues.
Alkalinization of intermediate-acting local anesthetics facilitates faster onset of the block during epidural anesthesia but does not have the same effect at the brachial plexus. Onset is not hastened by adding sodium bicarbonate to plain local anesthetic or to local anesthetic freshly mixed with epinephrine. Indeed, animal models have shown that alkalinization of local anesthetic reduces block intensity and duration.
Block Techniques for Major Approaches to the Brachial Plexus
A number of techniques involving various nerve localization modalities may be used for successful brachial plexus blocks, but only a sample can reasonably be presented in one chapter. When using ultrasound, target nerves can theoretically be imaged in short or long axis; target imaging is then combined with the needle guidance technique, in plane or out of plane, to fully describe the approach, for instance, short axis in plane or short axis out of plane. Since long-axis imaging for nerve blocks is limited to lower extremity techniques to date and in-plane needle guidance permits visualization of the tip of the needle, this chapter will cover only short-axis in-plane techniques using ultrasound.
Continuous Peripheral Catheters
Prolonged analgesia of the upper extremity can be accomplished with continuous perineural catheter techniques. Surgeries expected to cause prolonged, moderate to severe pain are appropriate for catheter placement. Such surgeries include total shoulder arthroplasty, rotator cuff repair, and major reconstructive operations on the elbow, wrist, or hand. Accumulated evidence suggests that perineural catheters can be managed efficiently in the ambulatory setting with a high degree of patient acceptance. Key to successful management is establishing clear lines of contact with the physician and patient. Even major surgeries such as total shoulder arthroplasty can be managed on an outpatient basis when perineural catheters are used to control pain and facilitate rehabilitation. Recent data indicate that ultrasound guidance can decrease the time needed to successfully place upper extremity perineural catheters in comparison to traditional nerve stimulation techniques. For infraclavicular perineural catheter insertion, ultrasound may reduce the incidence of unintentional vascular puncture when compared with nerve stimulation techniques. Limited data suggest that patient-controlled perineural analgesia techniques are superior to continuous infusion techniques. However, in the ambulatory setting, perineural infusion regimens that combine patient-controlled boluses with a continuous infusion rate are preferred.
Interscalene Block
Indications
For an interscalene block, the brachial plexus is approached at the level of its distal roots/proximal trunks. The most consistent local anesthetic distribution resulting from this approach involves the shoulder and upper part of the arm ( Fig. 53.3 ). The inferior trunk (C8, T1) is unaffected by local anesthetic in approximately 50% of cases, so an interscalene block is not recommended for surgeries involving the medial aspect of the upper part of the arm, the forearm, and the hand. Ultrasound-guided approaches are also likely to spare the lower trunk distribution, although some investigators describe targeting these nerves.
Techniques
Traditional Techniques
The brachial plexus traverses the interscalene groove, which is bordered by the anterior and middle scalene muscles. In the classic Winnie technique, the patient’s head is turned 30 degrees to the contralateral side, and then a 50-mm or shorter needle is inserted into the interscalene groove at the level of the sixth cervical vertebra. The needle is oriented perpendicular to all planes of the skin and then advanced with a slightly caudad angulation, which lessens the risk of entering the intervertebral foramen and encountering spinal nerves or the vertebral artery ( Fig. 53.4 ). The end point for advancement of the needle is either paresthesia or an evoked motor response (from peripheral nerve stimulation) in the arm or anterior aspect of the shoulder. Movement of the posterior portion of the shoulder indicates that the needle is too posterior and is stimulating the dorsal scapular nerve (C5), whereas a diaphragmatic motor response indicates placement of the needle too far anterior with resultant stimulation of the phrenic nerve. Once paresthesia or a motor response at approximately 0.5 mA is obtained, a 1-mL local anesthetic test dose is injected to rule out intravascular injection, followed by incremental injection of 20 to 30 mL of local anesthetic.
Borgeat and colleagues’ modified lateral interscalene approach has reportedly facilitated perineural catheter placement by reducing the angle that a catheter must take as it exits the block needle and enters the perineural area. Because the lateral approach directs the needle away from the vertebral column, this approach theoretically reduces the risk for injection of the vertebral artery or contact of the needle with the spinal cord or perispinal neural elements.
Ultrasound-Guided Technique
With the patient positioned as just mentioned, a high-frequency linear-array transducer should be placed at the level of the cricoid cartilage along the posterior border of the sternocleidomastoid (SCM) muscle ( Fig. 53.5 ). After identifying the SCM, the scalene muscles are reliably located deep to the SCM fascia posterior to the internal jugular vein and carotid artery. If the fascial plane between the anterior and middle scalene muscles (interscalene groove) is not easily visualized, slide the transducer caudad toward the clavicle while keeping the scalene muscles in the center of the screen until the interscalene groove widens to reveal the brachial plexus. Following infiltration of the skin and subcutaneous tissue with local anesthetic posterior to the transducer, advance the block needle in an anteromedial trajectory in plane through the middle scalene muscle and into the interscalene groove. Proceed with incremental injection of local anesthetic solution as described previously. In this region, successful interscalene blocks with injectate volumes of less than 5 mL have been reported. For perineural catheter insertion, placing the patient in the lateral decubitus position with the operative side up may facilitate this posterior approach when using ultrasound guidance.
Supraclavicular Block
Indications
The supraclavicular approach aims to encounter the brachial plexus at the juncture of the distal trunks and divisions as the brachial plexus courses under the clavicle and across the superior surface of the first rib ( Fig. 53.6 ). This area represents the most compact architecture of the brachial plexus, which has been postulated (but never proved) to explain the propensity of supraclavicular blocks for rapid onset and nearly complete anesthesia of the upper extremity. This block is indicated for any surgery on the arm (see Fig. 53.1 ), although shoulder surgery may require supplemental blockade of the supraclavicular nerve (C3-4) to ensure anesthesia of the cape area around the shoulder. A supraclavicular block is successful in approximately 95% of patients, including those who are obese.
Techniques
Traditional Techniques
A variety of techniques have been described for performing a supraclavicular block. With the patient in the supine position, the plumb bob technique places the needle just above the clavicle at the lateral border of the SCM muscle. The original description by Brown and associates involved directing the needle straight downward, similar to a brick mason’s plumb bob. If a motor response or paresthesia is not elicited, the needle is incrementally fanned 20 degrees cephalad and then 20 degrees caudad in the parasagittal plane until the desired motor response is obtained. In a modification of this technique, the initial needle pass is made 45 degrees cephalad, followed by incremental caudad angulation until a suitable paresthesia or motor response is obtained. The logic of this modification is that it reduces the risk for contact with the lung copula in tall individuals. If during the course of a supraclavicular block the needle encounters the subclavian artery, the needle should be redirected posteriorly and laterally to identify the brachial plexus. Injecting 20 to 30 mL of local anesthetic after a single paresthesia or motor response into the arm or shoulder at less than 0.5 to 0.9 mA completes the block procedure.
Ultrasound-Guided Technique
Using the same surface anatomic landmarks as presented for the traditional techniques, a high-frequency linear-array transducer is placed with its midpoint centered posterior to the clavicle and along the posterior border of the SCM ( Fig. 53.7 ). The subclavian artery is the most important sonographic anatomic landmark and helps localize the divisions of the brachial plexus, which is reliably superficial and posterior to the artery. With the transducer in this position, tilt the plane of the ultrasound beam more laterally to visualize the subclavian artery over the first rib. At this location the divisions of the inferior trunk, composed of C8 and T1, should be visualized in the “corner pocket” posterior to the subclavian artery and superficial to the first rib. The subclavian artery and brachial plexus at this level are still within the interscalene groove. After infiltration of the skin and subcutaneous tissue with local anesthetic posterior to the transducer, advance the block needle in an anteromedial trajectory in plane through the middle scalene muscle and into the interscalene groove. Ultrasound-guided supraclavicular perineural catheter insertion has been described with this approach, although there may be an analgesic advantage to using the infraclavicular technique for the postoperative management of patients undergoing distal upper extremity surgery. Alternatively, when using ultrasound guidance, the block needle may be directed in a posterolateral direction. Inject the local anesthetic solution incrementally and visually confirm spread of the injectate in the vicinity of the target nerves. Unlike an interscalene block, an ultrasound-guided supraclavicular block requires a volume of injectate similar to that used with the traditional techniques.
Infraclavicular Block
Indications
The infraclavicular block, which is indicated for surgery on the arm distal to the shoulder, approaches the brachial plexus at the level of the cords ( Fig. 53.8 ). This block anesthetizes the axillary and musculocutaneous nerves more reliably than does the axillary approach. Infraclavicular block techniques have the advantage of not requiring a specific arm position during placement, which is useful for patients with limited arm motion because of pain, casts, or dressings. The infraclavicular approach is frequently used for continuous perineural catheter placement because the catheters reliably remain in place during use. There have been reports of successful use of continuous infraclavicular perineural infusion for the treatment of complex regional pain syndrome of the upper extremity and for upper extremity limb salvage.
Techniques
Traditional Techniques
Similar to the supraclavicular approach, several techniques have been described for an infraclavicular block; none are inherently superior. The coracoid approach begins with identification of the lateral aspect of the coracoid process in a supine patient. From this point, an entry point 2 cm caudad and 2 cm medial is marked ( Fig. 53.9 ). A stimulating needle is directed posteriorly, perpendicular to all planes. Stimulation of the various cords can be ascertained by their resulting motor response—“at the cords, the pinkie towards.” Stimulation of the posterior cord causes the little finger to move posteriorly, stimulation of the medial cord results in medial movement, and stimulation of the lateral cord results in lateral movement. The posterior cord occupies the middle position and is the deepest of the three cords. Block success is maximized when two cords are identified and subsequently bathed with local anesthetic ; identification and subsequent injection around the posterior cord are the most important determinants of block success. A total of 30 to 40 mL of local anesthetic is sufficient for an infraclavicular block.
Ultrasound-Guided Technique
With the arm abducted 90 degrees and the coracoid process used as a surface landmark, the transducer is oriented in the parasagittal plane with its midpoint slightly medial and caudad to the coracoid process ( Fig. 53.10 ). Although a small-footprint, lower-frequency curvilinear transducer may have advantages because of this region’s limited space and the expected steep angle of the block needle, a high-frequency linear transducer may also be used in most nonobese patients. The optimal short-axis ultrasound image should demonstrate the axillary artery and the brachial plexus cords to be located immediately deep to the pectoralis minor muscle and its accompanying clavipectoral fascia. It is helpful to visualize the axillary artery as being in the center of a clock face, with the brachial plexus cords arranged around the artery in a parasagittal topographic arrangement. The exact position of the cords relative to the artery is variable, but the posterior cord is always located between the lateral and medial cords. Deep to the pectoralis minor muscle and clavipectoral fascia, the axillary artery is visualized cephalad to the axillary vein, where it is surrounded by the three brachial plexus cords. After infiltration of the skin and subcutaneous tissue with local anesthetic cephalad to the transducer, advance the block needle in a caudad direction through the pectoralis muscles toward the axillary artery. Local anesthetic may be deposited separately around each cord or via a single injection incrementally posterior to the axillary artery with comparable block efficacy. Similar to a supraclavicular block, injectate volume when using ultrasound guidance for an infraclavicular block does not seem to differ significantly from that used with traditional techniques. For distal upper extremity postoperative analgesia, many ultrasound-guided infraclavicular perineural catheter insertion techniques have been described. Continuous infraclavicular perineural infusions have been shown to provide postoperative analgesia that is superior to that achieved with supraclavicular perineural infusions after distal upper extremity surgery. A combination of continuous infusion and patient-controlled boluses optimizes analgesia when compared with either a basal-only or a bolus-only dosing regimen.
Axillary Block
Indications
The axillary block anesthetizes the brachial plexus at the level of the four terminal nerves: the radial, ulnar, median, and musculocutaneous nerves ( Fig. 53.11 ). It is indicated for surgeries distal to and including the elbow (see Fig. 53.1 ). With the exception of very proximal approaches high in the axilla, the axillary block is not as ideally suited for continuous catheter techniques as are the infraclavicular approach and approaches above the clavicle.
