Axillary block procedure guide

INTRODUCTION — The axillary block is a peripheral nerve block performed in the axilla and anesthetizes the terminal branches of the brachial plexus (figure 1). Axillary blocks are used for anesthesia and/or analgesia for surgery of forearm, wrist, hand, and fingers. This topic will discuss the anatomy, ultrasound imaging, and injection techniques for performing axillary plexus blocks. In this topic, the term axillary block will refer to axillary brachial plexus block, as opposed to axillary nerve block, which is discussed separately. (See "Upper extremity nerve blocks: Techniques", section on 'Axillary nerve block'.)

General considerations common to all peripheral nerve blocks, including patient preparation and monitoring, use of aseptic technique, localization techniques, drug choices, contraindications, and complications, are discussed separately. (See "Overview of peripheral nerve blocks".)

ANATOMY — The brachial plexus is formed by the ventral rami of the lower cervical and upper thoracic nerve roots (figure 2). The nerves of the brachial plexus (figure 1) travel through the neck, under the clavicle, and into the arm (figure 3). As the brachial plexus travels under the clavicle, the divisions form into posterior, lateral, and medial cords. As the cords pass between the clavicle and the axilla they run deep to the pectoralis major and pectoralis minor muscles. The axillary artery and the brachial plexus travel just cephalad to the axillary vein (figure 4 and image 1).

●Terminal branches – In the axilla the radial, median, and ulnar nerves lie in close proximity to the axillary artery and vein while the musculocutaneous nerve diverges from the other nerves, piercing the coracobrachialis. Nerve orientation around the axillary artery follows a typical pattern as described below, with considerable variability (image 1). (See 'Ultrasound imaging' below.)

The medial brachial cutaneous and medial antebrachial cutaneous nerves are branches of the medial cord of the brachial plexus, and run along with the ulnar nerve through the axilla.

●Innervation – The branches of the brachial plexus provide innervation of the arm below the shoulder, with the exception of the medial upper arm (intercostobrachial nerve, T2). Cutaneous sensory innervation of the upper extremity is shown in a figure (figure 5). Motor innervation of each terminal nerve is shown in a table (table 1).

Sensory and motor innervation are relevant for 1) pre-procedural assessment of existing neurological deficits, 2) post-procedure assessment of clinical effect of nerve block, and 3) assessment of needle-nerve proximity when using nerve stimulation techniques.

ANATOMIC CLINICAL CORRELATIONS — The axillary block provides anesthesia and analgesia for the elbow, forearm, and hand (figure 5). This block is performed at the level of the terminal branches of the brachial plexus, targeting the radial, median, ulnar nerves, and in addition, the musculocutaneous nerve (figure 6) [1].  

The musculocutaneous nerve block is sometimes considered a separate block from the axillary brachial plexus block because of its slight separation from the other nerves. However, because of its role in elbow flexion and sensory innervation of the lateral forearm, it should always be blocked when surgical anesthesia of the elbow, forearm, or wrist is the goal. As discussed here, it will be considered an essential part of the axillary brachial plexus block (figure 7 and table 1).

Local anesthetic (LA) spread to the intercostobrachial nerve is not expected with axillary block. Separate block of the intercostobrachial nerve is required when surgery involves a tourniquet or for an incision on the medial upper arm (table 1 and figure 8) [2].

An alternative brachial plexus block should be considered for patients who are unable to abduct the arm, since this position is required for axillary block placement.

The axillary block is a superficial technique. This facilitates ultrasound needle visualization and the ability to compress the brachial artery in the event of a vascular puncture.

AXILLARY BLOCK TECHNIQUE — Axillary block can be performed with ultrasound guidance, nerve stimulator guidance, or transarterial techniques. Greater success rates, shorter performance time, and lower local anesthetic (LA) volume requirement are possible with ultrasound-guided techniques compared with nerve stimulation, paresthesia, or transarterial techniques [3]. We suggest not deliberately eliciting paresthesias to localize nerves for this or other peripheral nerve blocks. (See "Overview of peripheral nerve blocks", section on 'Block guidance techniques'.)

Patient positioning — Position the patient supine with the arm abducted to 90 degrees, externally rotated at the shoulder, and the elbow flexed. The degree of abduction may be modified to achieve the best visualization of anatomy when ultrasound guidance is used.

Ultrasound-guided technique

Ultrasound equipment — Use a high-frequency linear ultrasound transducer (eg, 10-5 mHz). Set the depth at approximately 3 to 4 cm.

Ultrasound imaging

●Place the ultrasound transducer on the proximal arm at the level of the axilla, immediately caudal to the lateral border of the pectoralis major muscle and directly overlying the axillary artery. Orient the ultrasound beam superiorly (cephalad), perpendicular to the long axis of the humerus (picture 1).

●Identify the axillary artery (hypoechoic, pulsatile, and noncompressible), and the axillary vein deep and medial to the artery. Use color Doppler to confirm the axillary artery and vein and any other blood vessels within the needle path (movie 1).

●Deep to the artery, identify the conjoint tendon of the teres major and latissimus dorsi muscles and the deeper triceps muscle (image 1).

●Identify the median, ulnar, and radial nerves as hyperechoic structures often containing hypoechoic nerve fascicles (image 1). Nerve location relative to the artery is variable. It may be helpful to think of nerve location in four quadrants created by imaginary vertical and horizontal lines through the middle of the artery [4-7]. Each quadrant is likely but not certain to contain one of the four terminal nerves of the brachial plexus and should serve as a starting point for trying to identify the nerves. Based on three studies that used ultrasound along with nerve stimulator confirmation [4,5,7], typical positions for the branches of the brachial plexus with the transducer at the border of the pectoralis muscle, and the arm positioned for block, are as follows:

•The order of the nerves around the axillary artery is consistently median > ulnar > radial > musculocutaneous.

•The median nerve is in the superficial lateral quadrant in 85 to 92 percent of patients, most commonly in the middle third of that quadrant.

•The ulnar nerve is in the superficial medial quadrant in 89 to 95 percent of patients, superficial to the vein in 20 to 45 percent, and deep to the vein in 54 to 80 percent.

•The radial nerve is in the deep medial quadrant in 86 to 97 percent of patients.

•The musculocutaneous nerve is in the deep lateral quadrant in 85 to 90 percent of patients, most commonly in or near the coracobrachialis muscle, and instead near the axillary artery in 10 to 28 percent of patients.

Unlike the other three nerves, the musculocutaneous nerve may be identified at a distance away from the artery in the coracobrachialis muscle or between the coracobrachialis and biceps brachii muscle.

TIP: The musculocutaneous nerve travels obliquely through the arm, lying closer to the brachial plexus in the proximal axilla, and diverging from the plexus more distally. Thus scanning proximal to distal while following the course of the nerve can help identify it.

Performing the block — Two different approaches may be used for ultrasound-guided axillary block, either a perineural technique targeting individual nerves or a perivascular technique that targets circumferential spread around the artery. We use a perineural approach unless the individual nerves are difficult to identify. Both are highly effective approaches to axillary block. In a randomized trial comparing a single perivascular injection with individual perineural injections for axillary blocks in 50 patients, onset of the block was faster with perineural injection, but overall block success rates were similar [8].

●Infiltrate the skin and soft tissue at the injection site with 1% lidocaine, 1 to 3 mL, using a 25 gauge needle.

●Insert an echogenic B-bevel 20 to 22 gauge, 5 to 10 cm needle using an in-plane approach (picture 1 and picture 2), with a lateral to medial (cephalad to caudad) needle trajectory (movie 2).

●We often block the nerves in the following order: radial > median > ulnar musculocutaneous, though other sequences are reasonable. We target the radial nerve, which is deepest, before the median and ulnar nerves so that any inadvertently injected air will not obscure the more superficial structures. For radial, ulnar, and median nerves, adequate LA spread consists of either hypoechoic LA spread around the nerve (though fully circumferential spread is not necessary), or spread of LA between the nerve and the artery, with an ultimate goal of circumferential spread around the artery.

•Advance the needle tip to a position adjacent to the musculocutaneous nerve, keeping the entire needle throughout. After negative aspiration, inject 3 to 5 mL of LA, while visualizing spread of LA (movie 2 and movie 3).

•Withdraw the needle slightly and redirect posterior to the axillary artery, positioning the tip between the radial nerve and the axillary artery above the conjoint tendon. After negative aspiration, inject 8 to 12 mL of LA, while visualizing spread of LA.

•Withdraw the needle slightly and redirect superficial to the artery, passing over the artery to the quadrant containing the ulnar nerve (superficial, medial quadrant) while using caution to avoid passing the needle through the median nerve. After negative aspiration, inject approximately 8 mL of LA between the artery and ulnar nerve.

•Withdraw the needle to position the tip adjacent to the median nerve; after negative aspiration inject approximately 8 mL of LA between the artery and median nerve before removing the needle entirely. We inject at the ulnar nerve first, followed by the median nerve, though the reverse sequence is acceptable.

●If the radial, ulnar, and median nerves are difficult to identify individually, it is reasonable to inject the LA around the axillary artery while visualizing circumferential spread. Place the needle tip adjacent and deep to the artery, and after negative aspiration inject approximately 25 mL of LA in 5 mL increments, with gentle aspiration between injections.

Nerve stimulator-guided technique — Nerve stimulation can be used alone to perform the block, and can also be used for nerve confirmation during ultrasound-guided block.

Number of targeted nerves — Several techniques for performing nerve stimulator-guided axillary block have been described. They differ with respect to the number of individual nerves that are targeted (ie, median, radial, and ulnar) in addition to the musculocutaneous nerve. Most evidence suggests that block efficacy is improved if both the median and radial nerves are blocked, in addition to the musculocutaneous nerve, and that there is no benefit to adding a block at the ulnar nerve [9]. The decision regarding the number of injections represents a balance between increased block efficacy with multiple injections, versus the possibility of increased risk of nerve damage. The concern regarding nerve injury is that the initial injection might diminish or eliminate stimulation and/or paresthesias at subsequently injected nerves, thereby masking needle trauma to those nerves.

Examples of relevant studies include the following:

●In a randomized trial including 120 patients who underwent nerve stimulator-guided axillary block with one of four patterns of nerve stimulation, triple injection (ie, radial, median, and musculocutaneous) provided more complete anesthesia than injections at the radial or median nerves alone, or radial nerve plus musculocutaneous injections [10].

●In another randomized trial including 60 patients who received nerve stimulator-guided axillary block, three injections at radial, median, and musculocutaneous nerves provided more complete anesthesia, primarily in the median nerve distribution, than two injections at the radial and musculocutaneous nerves [11].

●In a randomized trial of 84 patients who underwent nerve stimulator-guided axillary block, block efficacy was similar with or without the addition of an ulnar nerve block to triple injection at the radial, median, and musculocutaneous nerves [12]. Block time was shorter and patient pain during the block was lower without the additional ulnar nerve block.

●In another randomized trial of 90 patients who received nerve stimulator-guided block with triple stimulation at the musculocutaneous and median nerves along with either radial or ulnar stimulation, overall block success was greater with radial stimulation [13].

In two of the studies described above, in several patients nerve stimulation was not possible for one of the intended nerve targets [10,11], which the authors felt was related to rapid onset of block after injection of LA at previously targeted nerves. If multiple injections are used, they should be performed quickly to minimize this effect and maintain the patient's ability to report paresthesias.

Nerve stimulation can also be used as an adjunct to ultrasound-guided block.

Nerve stimulation equipment — The authors use a nerve stimulator initially set to a pulse width of 100 ms at 2 Hz and an initial current of 1.0 mA. We use a shielded, B-bevel, 20 to 22 gauge 10 cm stimulating needle. Connect the stimulator to the needle and to an electrode on the patient's skin (picture 3). (See "Overview of peripheral nerve blocks", section on 'Equipment for nerve stimulator guidance'.)

Identify needle insertion site — Palpate the axillary artery in the axilla. The initial needle insertion site should be just superior to the pulse.

Performing the block — We describe a three injection technique, targeting the median, musculocutaneous, and radial nerves, in that order. Alternative sequences are also used.

●Infiltrate the skin and soft tissue at the injection site with 1% lidocaine, 1 to 3 mL, using a 25 gauge needle.

●For each nerve, observe the patient's ipsilateral hand and arm to assess the effects of nerve stimulation as the needle tip approaches the nerve. When appropriate stimulation occurs, decrease the stimulator current until the motor response disappears. Then turn the current up to the minimal current that results in a motor response. The goal is a minimal stimulation response between 0.2 and 0.5 mA. The presence of a motor response at <0.2 mA strongly suggests intraneural needle placement and the needle should be repositioned without injecting.

●For each nerve, use an LA solution with epinephrine as a vascular marker. Stop injection and redirect the needle if blood appears in the syringe, the patient complains of paresthesia, or there is resistance to injection.

●Median nerve block – Insert the needle at a 45 degree angle, directed proximally along and just lateral (cephalad) to the axillary artery, seeking median nerve stimulation (ie, flexion of the first three digits, thumb opposition, and/or lateral wrist flexion) (table 2). After confirming the appropriate stimulation level and after negative aspiration, inject 10 mL of LA solution containing epinephrine as a vascular marker in 5 mL increments, with gentle aspiration between injections.

●Musculocutaneous nerve block – Withdraw the needle without removing it from the skin, reset the stimulator to 1 mA current, and redirect the needle laterally (cephalad) into the coracobrachialis muscle, seeking evidence of musculocutaneous nerve stimulation (ie, elbow flexion) (table 2). After confirmation of the appropriate stimulation level and after negative aspiration, inject 6 mL of LA solution with epinephrine.

●Radial nerve block – Remove the needle, reset the stimulator to 1 mA current, and insert the needle at a 45 degree angle, directed proximally along and just medial (inferior) to the axillary artery pulse, seeking evidence of a distal radial motor response to stimulation (ie, finger or wrist extension). Ulnar stimulation may be encountered first; advance the needle further, redirecting if a paresthesia occurs. After confirmation of the appropriate stimulation level and after negative aspiration, inject 20 mL of LA solution in 5 mL increments with gentle aspiration between injections.

If proximal motor response to radial nerve stimulation occurs (ie, forearm extension), redirect the needle to obtain a distal motor response. In one randomized trial including 150 patients who underwent axillary block, block efficacy was lower and onset time slower when injection was performed after a proximal motor response was obtained, compared with a distal response [14].

If ulnar stimulation occurs (ie, flexion of the fourth and fifth digits with wrist flexion and ulnar deviation) when inserting the needle inferior to the artery, continue to seek radial nerve stimulation.

Transarterial technique — If ultrasound and nerve stimulation are not available, a transarterial technique is a reasonable alternative, though rarely used and much less preferred compared with ultrasound- or nerve stimulator-guided block. For this technique, a fine needle is used attached to a syringe that contains LA with epinephrine as a marker of intravascular injection. The needle is inserted through the axillary artery, while aspirating with the syringe. One-half of the total volume of LA is injected posterior to the artery, and one-half anterior to the artery, based on the inability to aspirate blood.

The reported success rate of transarterial block ranges from 60 to 90 percent, with 10 to 15 percent of patients requiring supplementation with additional blocks and a reported failure rate of approximately 1 percent [15-18]. Paresthesias are reported in up to 40 percent of transarterial blocks, though most resolve without consequence [18,19]. In a review of 1000 transarterial blocks, persistent paresthesia occurred in 2 patients, and resolved by one month after surgery [15].

Compared with nerve stimulator-guided blocks, transarterial blocks are associated with a higher incidence of paresthesia and lower block success rates. In a randomized trial including 100 surgical patients who had axillary block with 1% mepivacaine with epinephrine using multiple nerve stimulation guidance or a transarterial technique, initial block success rate was higher with nerve stimulator-guided block (88 versus 62 percent), and there were four times as many paresthesias with transarterial block (32 versus 8 percent) [18].

With the transarterial technique the musculocutaneous nerve is not specifically targeted, and it is less likely to be blocked than with ultrasound- or nerve stimulator-guided blocks [16].

DRUG CHOICE AND DOSING

●Local anesthetics – Local anesthetics (LAs) are chosen according to the goal of the block (surgical anesthesia or analgesia) and the desired duration of the effect of the block (table 3). LAs for peripheral nerve blocks and the use of adjuvant drugs are discussed in more detail separately. (See "Overview of peripheral nerve blocks", section on 'Drugs'.)

Choices of LA for axillary block are as follows:

•Surgical anesthesia only – 2% lidocaine or 1.5% mepivacaine.

•Postoperative analgesia – 0.25 to 0.5% bupivacaine or 0.5% ropivacaine.

•Surgical anesthesia and postoperative analgesia, either:

-For rapid onset – Equal volumes of a short-acting LA (2% lidocaine or 1.5% mepivacaine) plus a long-acting LA (0.5% bupivacaine or 0.5% ropivacaine). Note that mixing LAs results in block onset and duration that are both intermediate between the two agents [20].

-When rapid onset is not required (ie, 30 minutes for onset is acceptable) – 0.25 to 0.5% bupivacaine or 0.5% ropivacaine.

•When ultrasound guidance is not used, epinephrine 2.5 to 3.3 mcg/mL should be included in the injectate as a marker of intravascular injection.

●Volume of LA – Volumes of LA used in successful axillary brachial plexus block vary widely. The use of 15 to 30 mL of LA is most commonly described for ultrasound-guided axillary blockade [21-23]. However, significantly lower volumes have been used successfully, with one study reporting surgical anesthesia of the hand with the injection of 1 mL of LA around each nerve [24].

For nerve stimulator-guided block, 35 to 40 mL of LA solution is usually injected, with 10 mL at the median nerve, 6 mL near the musculocutaneous, and 20 mL at the axillary nerve [13].

CONTINUOUS AXILLARY BLOCK — Successful use of continuous axillary brachial plexus blockade has been described [25]. However, this technique is not in common usage. Axillary block catheters are associated with a relatively high risk of local inflammation and bacterial colonization [26]. Anatomically, the nerves of the brachial plexus begin to diverge in the axilla, making coverage of multiple nerves with a single catheter theoretically more challenging. Lastly, the high success of continuous infraclavicular and supraclavicular approaches may obviate the need for a continuous axillary approach.

SIDE EFFECTS AND COMPLICATIONS — Axillary blocks are generally safe, with few reported complications. The side effects and complications specific to the higher brachial plexus blocks should not occur with axillary block (ie, pneumothorax, phrenic nerve palsy, Horner syndrome, and hoarseness) [27]. Complications common to all peripheral nerve blocks (eg, nerve injury, bleeding, local anesthetic [LA] systemic toxicity, infection) are discussed separately. (See "Overview of peripheral nerve blocks", section on 'Complications'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Local anesthetic systemic toxicity" and "Society guideline links: Local and regional anesthesia".)

SUMMARY AND RECOMMENDATIONS

●Anatomy

•The brachial plexus is derived from the lower cervical and upper thoracic nerve roots (figure 2). The nerves of the brachial plexus (figure 1) travel through the neck, under the clavicle, and into the arm (figure 3 and figure 4).

•The axillary block is performed at the level of the terminal branches of the brachial plexus.

•Axillary block is used for surgery of the arm at or below the elbow (figure 9). (See 'Anatomy' above and 'Anatomic clinical correlations' above.)

●Block technique – We use an ultrasound-guided perineural injection approach for axillary block. We routinely include a musculocutaneous nerve block. If ultrasound is unavailable, nerve stimulator-guided block or rarely, a transarterial approach, are reasonable alternatives. Position the patient supine, with the arm abducted to 90 degrees. (See 'Patient positioning' above.)

•Ultrasound-guided technique – We perform ultrasound-guided axillary block as follows, with further explanation above (movie 2). (See 'Ultrasound-guided technique' above.)

-Use a high frequency (eg, 10-5 MHz) linear ultrasound transducer, with the depth set to 3 to 4 cm.

-Place the transducer in the proximal arm at the axilla, immediately posterior to the pectoralis major muscle and oriented perpendicular to the humerus (picture 1).

-Identify the musculocutaneous nerve within the coracobrachialis muscle, the axillary artery, and the median, ulnar, and radial nerves around the artery; the median nerve is often superficial, ulnar nerve is often medial, and the radial nerve is typically posterior to the artery (image 1) .

-Block each of the four nerves individually (movie 2). After negative aspiration, inject 3 to 5 mL local anesthetic (LA) solution at the musculocutaneous nerve, 8 to 12 mL LA at the radial nerve, and 8 mL each at the median and ulnar nerves, visualizing spread of LA around the nerves (movie 3).

•Nerve stimulator-guided technique – Nerve stimulation can be used for block guidance or to confirm the nerve(s) during ultrasound-guided block. A triple injection technique targeting the median, musculocutaneous, and radial nerves may be more effective than a technique targeting fewer nerves. We describe blocking the nerves in the sequence median > musculocutaneous > radial, though alternatives are also used. For each nerve, after confirmation of minimal appropriate motor response between 0.2 and 0.5 mA and after negative aspiration, inject LA solution containing epinephrine as a vascular marker as described, in increments ≤5 mL, with gentle aspiration between injections (table 2). (See 'Nerve stimulator-guided technique' above.)

-Insert a stimulating block needle just superior to the axillary artery pulse in the axilla at a 45 degree angle directed proximally along and just superior to the artery, seeking median nerve stimulation (ie, flexion of the first three digits, thumb opposition, and/or lateral wrist flexion) (table 2). Inject 10 mL of LA solution.

-Withdraw the needle without removing it from the skin, and redirect into the coracobrachialis muscle, seeking musculocutaneous nerve stimulation (ie, elbow flexion). Inject 6 mL of LA solution.

-Remove the needle, reinsert just inferior to the axillary pulse, seeking a distal motor response indicative of radial nerve stimulation (ie, finger or wrist extension). Inject 20 mL of LA solution.

•Transarterial technique – If ultrasound and nerve stimulation are not available, a transarterial technique may be used, though much less preferred. A fine needle is inserted through the axillary artery, while aspirating with the syringe. Half of the total volume of LA is injected posterior to the artery, and half anterior to the artery, based on the inability to aspirate blood. (See 'Transarterial technique' above.)

●Drug choice – LA choices for axillary block are as follows (see 'Drug choice and dosing' above):

•Surgical anesthesia only – 2% lidocaine or 1.5% mepivacaine.

•Postoperative analgesia – 0.25 to 0.5% bupivacaine or 0.5% ropivacaine; for continuous block, infusion of 0.2% ropivacaine or 0.125% bupivacaine.

•Surgical anesthesia and postoperative analgesia, either:

-For rapid onset – Equal volumes of a short-acting LA (2% lidocaine or 1.5% mepivacaine) plus a long-acting LA (0.5% bupivacaine or 0.5% ropivacaine)

-When rapid onset is not required (ie, 30 minutes for onset is acceptable) – 0.25 to 0.5% bupivacaine or 0.5% ropivacaine.

•When ultrasound guidance is not used, epinephrine 2.5 to 3.3 mcg/mL should be included in the injectate as a marker of intravascular injection.