Chapter 28. Axillary Brachial Plexus Block

Brachial plexus block at the level of the axilla is typically chosen for anesthesia of the distal upper limb. Axillary block is a basic regional anesthesia technique and perhaps the most common approach to brachial plexus blockade. Low risk of serious complications, superficial location, and good analgesia of the upper arm muscles make this block suitable for ambulatory procedures of longer duration that require a tourniquet.

The surgical technique of this block was first described by Hall1 in New York (Roosevelt Hospital) in 1884, and the percutaneous technique was described by Hirschel2 in 1911. While dissecting the axilla in a child in 1958, Burnham,3 recognized that filling the neurovascular sheath with local anesthetic could simplify the axillary block. He also described the characteristic fascial “click” felt on penetration by the needle. In 1961 while using the formula for a cylinder volume, De Jong4 calculated that in an average adult, 42 mL of local anesthetic (LA) was necessary to fill the fascial compartment to the level of the cords and block all terminal nerves to the arm. A year later, Eriksson and Skarby,5 in an effort to promote the proximal spread of LA, advocated wrapping a rubber tourniquet around the arm, distal to the needle. In 1979, Winnie and coworkers6 found the tourniquet ineffective and painful and recommended firm distal digital pressure on the neurovascular sheath instead. In addition, they also recommended arm adduction after LA injection, thinking that the head of the abducted humerus compressed the neurovascular sheath. Both maneuvers were later proved to be clinically ineffective.7–9 Thompson and Rorie,10 in 1983, studied brachial plexus using computed tomograms and suggested that the median, ulnar, and radial nerves lie in separate fascial compartments within the neurovascular sheath; this finding provided a rational explanation for incomplete blocks. However, anatomic studies by Lassale and Ang11 in 1984 and Vester-Andersen and coworkers12 in 1986 did not confirm the existence of a true neurovascular sheath. The interfascial space they found contained the median and the ulnar nerves, infrequently the musculocutaneous, and occasionally the radial nerves. Moreover, the space was suggested to communicate proximally only with the medial cord of the plexus. In 1987 Partridge and coworkers13 described the interneural septa, which were easily broken by injection of dyed latex. In 2002 Klaastad and coworkers14 were the first to investigate the spread of the LA through the axillary catheter in studies using magnetic resonance imaging (MRI) scanning. They found that in most patients the spread of LA was uneven and the clinical effect inadequate.

Until the 1960s, the prevalent block techniques were double or multiple axillary injections. After the concept of the neurovascular sheath had been established by De Jong4 in 1961, the single-injection technique, being the simplest, became standard. However, Vester-Andersen and coworkers15,16 demonstrated in 1983 and 1984, that despite high volumes of LA, analgesia was often inconsistent (“patchy”). In the early 1990s, the double-injection, transarterial technique was popularized by Urban and Urquhart17 and Stan and coworkers.18 More recently, however, development of peripheral nerve stimulators and insulated atraumatic needles has allowed electrolocation and separate blockade of the individual terminal nerves (median, musculocutaneous, ulnar, and radial). This is known as the multiple-nerve stimulation technique. Baranowski and Pither19 (in 1990), Lavoie and coworkers20 (in 1992), Koscielniak-Nielsen and coworkers21,22 (in 1997 and 1998), and Sia and coworkers23,24 (in 2001 and 2002), independently showed that multiple-nerve stimulation was superior, both to the single- and the double-injection methods by increasing the success rate and shortening the block onset. A recent Cochrane review by Handoll and coworkers25 validated these findings.

The most common indications for axillary block include surgery of the forearm, wrist, or hand of moderate to long duration, with or without arm tourniquet. Relative contraindications to the use of this block are skin infection at the block site, axillary lymphadenopathy, and severe coagulopathy. In addition, this block is best avoided in patients with severe preexisting neurologic disease of the upper extremity because sensory assessments may be difficult.

In the apex of the axilla, the three plexus cords (lateral, medial, and posterior) form the main terminal nerves of the upper extremity (axillary, musculocutaneous, median, ulnar, and radial). However, only the last three nerves accompany the blood vessels through the axilla where the blocks are performed (Figure 28–1), while the axillary and the musculocutaneous nerves leave the plexus approximately at the level of the coracoid process. The axillary nerve departs at a wider angle from the posterior cord, laterally and dorsally, and the musculocutaneous nerve, which originates from the lateral cord, runs obliquely laterally into the coracobrachial muscle and continues downward. The medial antebrachial and brachial cutaneous nerves run subcutaneously parallel to the axillary vessels, although the medial antebrachial cutaneous nerve often follows the median nerve within the neurovascular sheath. In the axilla, the median and musculocutaneous nerves lie superior to the artery, whereas the ulnar and radial nerves lie inferior to it. The depths at which the nerves are found vary. Typically, the median nerve is more superficial than the musculocutaneous, and the ulnar nerve is more superficial than the radial. Occasionally, the radial or the musculocutaneous nerves (or both) are found behind the artery. These two nerves progressively diverge from the neurovascular sheath, continuing down the upper arm, the musculocutaneous above (anterior) and the radial below (posterior) to the humerus, where they can be approached using the midhumeral approach.26

Landmarks

Surface landmarks for the axillary brachial plexus block include (Figure 28–2):

• 1. Pulse of the axillary artery
• 2. Coracobrachialis muscle
• 3. Pectoralis major muscle
• 4. Biceps muscle
• 5. Triceps muscle

• Sterile towels and 4-in. × 4-in. gauze packs
• Sterile gloves, marking pen, and a skin electrode
• 1-in., 25-gauge needle for skin infiltration
• 1- to 1.5-in. atraumatic, insulated stimulating needle
• 20-mL syringes containing LA of choice
• Peripheral nerve stimulator

Arm Position for the Block

The arm to be operated on is abducted approximately 90 degrees (see Figure 28–2). The elbow is flexed and the forearm rests comfortably, supported by a pillow. A skin electrode is typically placed on the patient's shoulder and connected to the positive electrode (anode) of the nerve stimulator. After scrubbing the axilla, the arterial pulse is palpated at the level of the major pectoral muscle, and the subcutaneous tissue overlying the artery is infiltrated with 4 to 5 mL of LA (to block the intercostobrachial and medial cutaneous nerves of the arm). Numerous techniques and approaches to the brachial plexus block at the level about the axilla have been described. Discussion of all the technique variations is beyond the scope of this text; we will describe some of the best studied and clinically useful techniques.

Single-Injection (Stimulation) Technique

• 1. The nerve stimulator is set to deliver 0.5–1.0 mA (2 Hz, 0.1 msec); electrical connections with the needle and the neutral electrode are checked.
• 2. Depending on the surgical site (palmar and medial or dorsal and lateral aspects of the hand/forearm), the stimulating needle is inserted above the arterial pulse (toward the median nerve) or below the arterial pulse (toward the radial nerve), respectively (Figures 28–3 and 28–4).
• 3. As the brachial superficial fascia is penetrated, a characteristic “click” is often felt, and the current amplitude is slowly increased (eg, at 1-mA increments) until the desired twitch (flexion or extension of the wrist and fingers) is obtained. This helps avoid painful electrical paresthesia when the elastic fascia suddenly “gives in” and the needle enters the neurovascular sheath.27
• 4. After the initial motor response is obtained, the needle is slowly advanced toward the stimulated nerve while reducing the amplitude.
• 5. Once the stimulation is obtained using a current intensity of 0.3 to 0.5 mA, the entire volume of LA is injected slowly, while intermittently aspirating to reduce the risk of accidental intravascular injection. This results in substantial spread of the LA within the tissue layers encompassing the brachial plexus (Figure 28–5).

Double-Injection Technique

• 1. The stimulating needle is first inserted above the artery, below the coracobrachialis muscle (see Figure 28–3). After penetrating the fascia, the amplitude is increased until synchronous wrist flexion/pronation and flexion of the first three fingers are obtained (median nerve stimulation). The needle is advanced slowly toward this nerve while reducing the amplitude to 0.3 to 0.5 mA. At this point, half of the planned volume of LA is slowly injected with intermittent aspiration to rule out intravascular injection.
• 2. The needle is then withdrawn and inserted below the artery and above the triceps muscle (see Figure 28–4). The fascia is again penetrated and the amplitude slowly increased. The first response is usually either arm extension (muscular branches to the triceps) or thumb adduction and flexion of the last two fingers (ulnar nerve). However, these responses are ignored, and the needle is advanced deeper, often slightly upward, behind the artery (Figure 28–6) until wrist and finger extension is obtained (radial nerve). After stimulation is obtained using a current intensity lower than 0.5 mA, the remaining volume of LA is slowly injected with intermittent aspiration.

Multiple-Injection Technique

Needle insertion sites are identical to those for the double-injection technique

• 1. After electrolocation of the median nerve, 5–10 mL of the LA volume is injected (see Figure 28–3).
• 2. The needle is withdrawn subcutaneously and redirected obliquely, above and into the coracobrachialis muscle. After obtaining stimulation-synchronous elbow flexion, the amplitude is reduced to 0.3 to 0.5 mA and another 5–10 mL of LA is injected.
• 3. The needle is removed and inserted below the artery (see Figure 28–4). The first stimulated nerve is usually the ulnar, into which 5–10 mL of LA is injected.
• 4. The needle is advanced deeper until the radial nerve is found (see under Double-Injection Technique.)

Transarterial Technique

The transarterial technique is perhaps most commonly used for axillary blockade. This relatively simple technique does not rely on a nerve stimulator; instead, placement of the needle within the neurovascular sheath is ensured by relying on the pulse of the axillary artery:

• The axillary artery is palpated and stabilized using a two-finger palpation technique.
• As the needle is advanced toward the pulse of the axillary artery, bright red arterial blood is aspirated. A thin, long-beveled needle (typically 1.5-in., 25-gauge) is used to minimize the risk of axillary hematoma.
• The needle is advanced deeper until blood cannot be aspirated (the tip of the needle has exited the artery) and half of the volume of the LA is injected behind the posterior wall. This should block the radial nerve.
• The needle is slowly withdrawn while aspirating. As the needle enters the axillary artery, bright red blood is again aspirated.
• The withdrawal of the needle is continued until blood can not be aspirated (the needle exits the artery and its tip is positioned superficial [medial] to the artery inside the neurovascular sheath).
• The remaining volume of LA is injected superficial to the anterior wall to block the median and the ulnar nerves.

Continuous Axillary Brachial Plexus Block Technique

Continuous axillary brachial plexus block is similar to the single-injection technique; nerve stimulator technique is typically used. The needle of choice is connected to the nerve stimulator, and the desired twitch response is sought. Once the stimulation is obtained with a current close to 0.5 mA, a catheter is advanced 5–8 cm cephalad into the neurovascular sheath. When a stimulating catheter is used, a nonconducting solution (eg, 5% dextrose29) can be injected through the catheter to dilate the sheath and facilitate insertion of the catheter. The catheter is secured using either a tunneling technique or application of a sterile clear dressing.

The difference between the multiinjection axillary and the midhumeral (humeral canal) approaches is that in the latter, the two terminal nerves, the musculocutaneous and the radial, are blocked above and below the humeral bone, respectively (Figure 28–7). With any multistimulation technique, there is always a risk that an intraneural injection may be made into the already anesthetized nerves. For that reason, theoretically, the midhumeral approach may carry a lower risk of neurologic complications because the nerves are farther apart.

Although the four-injection midhumeral block has been found to be more effective than the double-injection axillary technique,30 either block results in a high success rate when four injection techniques are used.24 An advantage of the axillary approach is that incomplete axillary blocks can be supplemented with a midhumeral block.31 The opposite is not possible, nor is it recommended because electrostimulation may be precluded by blockade distal to the site of nerve localization. An incomplete midhumeral block, on the other hand, can be supplemented at the elbow or the wrist.

Technique

The injection technique for the midhumeral block is similar to the four-injection axillary technique, except the injections are made more distally. In addition, the musculocutaneous and the radial nerves are sought at a deeper location than in the axillary approach (see Figure 28–7). Figure 28–8 demonstrates the spread of the injected local anesthetic in the midhumeral technique.

• The anesthesiologist's nondominant hand grips the biceps muscle while searching for the musculocutaneous nerve, and the stimulating needle is inserted below the muscle (to avoid direct stimulation).
• When the bone is contacted before eliciting the twitches, the needle is redirected upward, toward the belly of the biceps muscle.
• The triceps muscle is stabilized similarly while attempting stimulation of the radial nerve. It should be kept in mind that the radial nerve winds around the humeral shaft on its way downward, which makes electrolocation of this nerve challenging with distal approaches.

The choice of LA depends on the length of surgery and the desired density and duration of blockade. For single-injection blocks, short- and medium-acting LAs (prilocaine, 2-chloroprocaine, lidocaine, or mepivacaine) in concentrations of 1.5% to 2% (3% for 2-chloroprocaine), with or without epinephrine or sodium bicarbonate, will provide reliable sensory and motor block of rapid onset (10–20 min) and sufficient duration (3–4 h; 1.5–2 h for 2-chloroprocaine) for most common surgical procedures (wound debridement; closed fracture repositions; ligament-, tendon-, or nerve sutures; finger amputations; etc). For elective procedures of longer duration (arthrodeses, arthroplasties, osteosyntheses, extensive palmar fasciectomies, etc) ropivacaine 0.5–0.75% or bupivacaine 0.375–0.5%, with or without epinephrine, will provide analgesia of slightly slower onset (15–20 min) and longer duration (6–16 h). For specialized hand surgery that may last several hours—for example, multiple joint replacements or reimplantations of severed extremities—a continuous ropivacaine (0.2–0.375%) infusion via an axillary catheter is probably the best technique. Clonidine (0.5 mcg/kg) may be added to intermediate-acting LAs to prolong analgesia after single-shot blocks.32

The multiple-nerve stimulation technique is uncomfortable to patients27,33 and should be preceded by adequate premedication (eg, midazolam + sufentanil).34 Adequate sedation and analgesia not only improve patients' acceptance of the block but also help relax the arm muscles. This makes precise needle manipulation as well as eliciting and interpreting the motor responses to nerve stimulation significantly easier for the practitioner and more acceptable to patients.

The onset and distribution of analgesia can be tested every 5 or 10 min after block administration in the sensory areas of the terminal nerves (Figure 28–9). Thirty minutes after block insertion, the unblocked nerves can be supplemented distal to the initial block site (eg, elbow blocks).

The indications for continuous axillary block include control of acute postoperative pain, management of chronic pain, and treatment of vascular disease, (eg, Raynaud syndrome).

Technique

The axillary fossa is best shaved and disinfected. After subcutaneous LA infiltration, the specific muscle twitch from the nerve of greatest interest is elicited by a needle or stimulating introducer cannula (see section on the Single-Injection (Stimulation) Technique). The intensity of the stimulating current is progressively reduced to 0.5 mA or less, while making fine adjustments to the cannula's position. A catheter is inserted (under sterile conditions) 5–8 cm cephalad into the neurovascular sheath and either sutured to the skin or tunneled. This helps maintain the catheter in place because the nerves are superficial and the arm sweat makes maintenance of an occlusive dressing difficult.

Maintenance

Diluted solutions of long-acting LAs (eg, 0.125% bupivacaine or 0.2% ropivacaine) are most often used for continuous infusions. Ropivacaine is preferable because of its relative sparing effect on the motor neurons and its lower cardiotoxicity.

Different modes of LA administration may be employed: a continuous basal infusion, repeated boluses, and a combination of both (in which a bolus administration is patient-controlled). The first is limited by the size of pump's reservoir, for example, a 250-mL reservoir at 10 mL/h will last only 1 day. The combination of baseline infusion and boluses offers the advantage of adjusting the level of analgesia to individual needs and puts the patient “in charge” of pain control (which has an important psychological aspect). A typical infusion regimen for 0.2% ropivacaine is a basal rate of, for example, 0.1 mL/kg bodyweight per hour (minimum, 5 mL; maximum, 10 mL) and a 5 mL patient-controlled bolus with a lock-out time of 30 min. Such a regimen may be maintained for 2 to 3 days for the treatment of acute postoperative pain and as long as necessary in the chronic conditions.

Complications of Axillary Blocks

Acute

Vascular Puncture

Vascular puncture is frequent; however, intravascular injection usually can be avoided by repeated careful needle aspiration. However, venous puncture may go undetected when vigorous aspiration collapses the venous lumen.

Intravascular LA Injection

Intravascular LA injection (see earlier discussion) typically presents as lightheadedness and or tachycardia (ropivacaine- or epinephrine-containing solutions). Intraarterial injection produces hand paresthesia during injection, accompanied by sudden paleness, which may last a couple of minutes. Intravascular injection of a large LA dose may lead to loss of consciousness, seizures, and cardiac arrest. Slow injection with repeated needle aspirations is mandatory.

Hematoma

Hematoma may occur after arterial puncture, especially with large-bore blunt needles and in older patients. If the artery is punctured, firm, steady pressure should be applied over the puncture site for 5 to 10 min. For the transarterial technique, needles of smaller gauge should be used to minimize the risk of hematoma.

Toxicity Due to Absorption of LA

Toxicity due to absorption of LA (in contrast to the accidental intravascular injection, which becomes symptomatic during or immediately after the injection) usually becomes symptomatic 5–30 min after injection. The symptoms include lightheadedness, dizziness, tunnel vision, circumoral paresthesia, brady- or tachycardia, anxiousness (eventually progressing to unconsciousness), and seizures. Oxygen, a sedative/hypnotic in repeated, small doses, and airway support if necessary should be immediately administered.

Subacute & Chronic

Nerve Injury

Nerve injury may be caused by the advancing needle, intraneural injection, application of a tourniquet, or a combination of these. Intraneural injections are characterized by pain, extremity withdrawal, and resistance to injection. Needle and injection injuries typically manifest as neurologic deficit in the distribution of the affected nerve. Ischemic damage caused by prolonged application of the tourniquet more commonly results in a diffuse injury, affects several nerves, and is usually accompanied by soreness of the upper arm. Symptoms of nerve damage (sensory loss and persistent paresthesia) usually appear within a day or two after recovery from the block. Most nerve injuries are neurapraxia (functional damage), which carry a good prognosis and heal within a few weeks.

For axillary brachial plexus block, a triple-injection nerve stimulator technique with electrolocation of median, musculocutaneous, and radial nerves is preferred. This technique is probably the best compromise with regard to block success rate, onset, and simplicity. A double-injection technique is the next best and may be used with or without a nerve stimulator. The midhumeral (a four-injection technique) is probably best suited for supplementing incomplete axillary blocks, although it can be used as a primary technique. For continuous blocks, a catheter should be placed close to the main nerve innervating the surgical site (eg, the median nerve for surgery of medial and volar surfaces; the radial nerve for surgery of lateral and dorsal surfaces). For more extensive surgery involving the entire circumference of the arm (eg, major trauma/amputation), an approach higher in the axilla or infraclavicular block may be better suited. An optimal perineural infusion technique is the basal rate with patient-controlled boluses; the suggested LA for this application is ropivacaine 0.2%. An accidental intravascular injection is the most common complication of axillary block. The risk of systemic toxicity of LA can be decreased by avoiding fast, forceful injection and using frequent aspiration to rule out intravascular injection. Pain, paresthesia, extremity withdrawal or high injection pressure may indicate intraneural needle placement; occurrence of any of these signs and symptoms should prompt immediate cessation of the injection and reevaluation.