Peripheral Nerve Blocks

Aimee Pak

Peripheral Nerve Block: Background

Interest in regional anesthesia (RA) has renewed since the turn of the 21st century due to the changing landscape of American health care, greater awareness of pain management and its health effects, and the societal consequences from the opioid crisis.

Benefits of Regional Anesthesia

Poorly controlled acute pain may cause multisystem morbidity, negatively affect sleep, disturb mood, impair physical functionality, and worsen overall quality of life.¹ Acute pain may lead to chronic pain after surgery and has a high incidence (10%-60%) after common surgical procedures: hernia repair (6.2%), abdominal hysterectomy (9.9%), and thoracotomy (19.1%) at 12 months postoperatively.¹ Poorly controlled pain on the day of surgery is a risk factor for opioid use beyond 6 months,¹ which contributes to the U.S. opioid epidemic.

Therefore, potential benefits of RA programs have been investigated. One study that analyzed 13 897 regional anesthetics at an orthopedic ambulatory surgery center reported that 94% of patients had no or mild postoperative pain on the day of surgery, 67% by the first postoperative day, and 76% by the second postoperative day.² In contrast, a U.S. survey of 300 ambulatory patients reported 29% having mild pain in the immediate postoperative period.³

Mechanism of Peripheral Nerve Blockade

The peripheral nerve contains cablelike neural fibers within multiple bundling levels. The outermost epineurium is the layer surrounding connective and adipose tissue, extrinsic blood vessels, and fascicles.⁴,⁵ Each fascicle has a perineurium encasing a longitudinal collection of axons, intrinsic blood vessels, and surrounding endoneurium.⁴ The axon is the cytoplasmic projection of a neuron and is associated with myelin from Schwann cells.⁵ Axons may divide and join neighboring fascicles.⁴ The number of fascicles and the nonneural to neural tissue ratio increases when moving distally along a peripheral nerve.⁴

Local anesthetics (LA) block sodium channels to interrupt axonal impulse propagation.⁴ Pharmacological factors contribute to differences in individual LA clinical properties: (1) P_ka (inversely related to onset of action), (2) protein binding (inversely related to duration), and (3) lipid solubility (directly related to potency).

After equilibrating with the surrounding tissue and penetrating the thick vascular perineurium, a significantly reduced amount of the LA will ultimately reach its effector site.⁴ LA volume and concentration will affect its diffusion and perineurium penetration, respectively.⁴ Both are important as a high-volume, low concentration solution may result in an incomplete conduction blockade.⁴,⁵ Thicker peripheral nerves with greater neural tissue density require higher concentration but lower volume.⁴ Additional factors contribute to variations in conduction blockade but are beyond the scope of this chapter.

Peripheral Nerve Block: Complications

Unfortunately, several general complications may occur with peripheral nerve blocks (PNBs). Complications specific to a certain nerve block procedure will be addressed in the next section.

Peripheral nerve injury (PNI) is an uncommon complication that is reported to occur 2-4 per 10 000 blocks.⁶ Transient postoperative neurologic symptoms, however, are common though with good prognosis.⁶ The degree of axonal disruption determines severity and long-term prognosis of PNI: neuropraxia (damage limited to myelin sheath; recovery within weeks to months), axonotmesis (axonal injury; prolonged and potentially incomplete recovery), and neurotmesis (complete nerve transection; requires surgical intervention with uncertain recovery).⁵
The mechanism of PNI are broadly categorized as: mechanical (traumatic or injection), vascular (ischemic), and chemical (neurotoxic).⁵,⁶ Direct needle-to-nerve trauma or trauma from a high-pressure intraneural injection may occur, particularly if the perineurium or fascicle is disrupted.⁵,⁶ Fortunately, the perineurium may be difficult to penetrate with short-beveled, blunt tipped needles,⁷ such as with commercially available PNB needles. Ischemia from direct vascular injury, occlusion of the vasa nervorum feeding arteries, or compression from hematoma formation within the nerve sheath may cause PNI.⁵ Chemical injury from PNB injectate may cause an acute inflammatory reaction or chronic fibrosis.⁵ LA concentration, duration of exposure, and injection proximity to a fascicle all may affect LA neurotoxicity.⁵
Avoidance of intraneural injection and careful evaluation of RA performance under heavy sedation or general anesthesia are advised.⁵ However, PNB have not been found to be an independent risk factor for PNI.⁶ There are multiple other etiologies for perioperative PNI: surgical factors (positioning, traction, stretch, transection, compression injuries) and patient factors (metabolic derangements, hereditary conditions, vascular disease, entrapment neuropathies, preexisting neural compromise [ie, “double crush”]).⁵,⁶
Local anesthetic systemic toxicity (LAST) is a rare but potentially fatal complication with a reported incidence ranging from 0.04 to 0.37 per 1000 PNB based on registry data.⁸ Acute toxicity occurs when LA inhibits sodium, calcium, and potassium movement through their channels in central nervous system cells and cardiac myocytes. Thus, its classical presentation involves rapidly progressing neurological and cardiovascular symptoms that are initially excitatory (eg, agitation, auditory changes, metallic taste, seizures; tachycardia, hypertension, arrhythmias) then inhibitory (eg, respiratory arrest, coma; bradycardia, depressed cardiac conduction, cardiac arrest).⁷ However, nearly two-thirds of cases from 2014 to 2016 have atypical presentations (only cardiovascular or central nervous system symptoms) or delayed presentations beyond 5 minutes after injection (up to 12 hours after injection).⁸
While no RA technique or single factor can prevent LAST occurrence, risk mitigation strategies are critical: avoidance of vascular injection, minimizing LA systemic uptake, utilizing ultrasound guidance (USG), and recognition of susceptible populations.⁸ Additionally, rapid recognition of prodromal signs and initiation of appropriate management, which may include lipid rescue therapy, is important.
Pneumothorax is a potential complication of thoracic nerve blocks (eg, paravertebral nerve block) and with certain approaches to the brachial plexus (ie, interscalene and supraclavicular). Based on the International Registry of Regional Anesthesia (IRORA) data, there is an incidence of 6.6 per 10 000 blocks.⁹
Infection caused by PNB appear to be uncommon (0.86 per 10 000).⁹ It may occur more frequently with indwelling peripheral nerve catheter, despite aseptic techniques, with reported bacterial colonization rates from 7.5% to 57% depending on location (highest
with femoral and axillary catheters) and number of colonies used to define colonization.⁷ Needle puncture though active infectious sites should be avoided.¹⁰
Vascular puncture and hematoma formation may occur with any invasive procedure. Larger-bore needles (such as for nerve catheter placement), number of attempts, and any coagulopathy may increase the risk for blood loss or hematoma development.¹⁰ IRORA data reported block-related hematoma, including retroperitoneal hematoma, formation at 12 per 10 000 and arterial puncture at 39 per 10 000.⁹ Injection site compressibility should be taken into consideration, particularly with concurrent anticoagulation therapy.¹⁰ The 2018 fourth edition guidelines by the American Society of Regional Anesthesia (ASRA) address this concern specifically and recommend applying neuraxial anticoagulation guidelines similarly for any perineuraxial, deep plexus, or deep peripheral block.¹¹

Preparation and Technique

Monitoring and Sedation

Cardiopulmonary monitoring with intermittent or continuous blood pressure monitoring, continuous electrocardiography, and pulse oximetry is mandatory.¹² RA complications may present as conduction abnormalities, hemodynamic instability, or hypoxia. Since light sedation is commonly provided during RA procedures, oxygenation and ventilation monitoring is important. Supplemental oxygen should be administered, and capnography may be utilized.¹² Sedation should be carefully titrated, as loss of patient feedback may increase risk for nerve injury.¹⁰ Certain patient populations (eg, pediatrics, developmentally disabled) may benefit from general anesthesia for safe RA placement despite the risk for nerve injury.⁶

Emergency and Resuscitation

Rapid access to emergency equipment, devices, and drugs is necessary at all RA locations. Oxygen source and delivery, suction capability with associated canisters and tubing, airway management devices and equipment (eg, laryngoscope handle and blades, various sizes of endotracheal tubes, mask-valve ventilation device, supraglottic airways, oral and nasal airways, stylets, gum elastic bougies), syringes and needles in multiple sizes are necessary.¹³

Patients undergoing RA must have ready intravenous access to administer resuscitative drugs and fluids. Emergency drugs should include vasopressors (eg, phenylephrine, ephedrine), vasodilators (eg, labetalol), chronotropic agents (eg, atropine, glycopyrrolate), rapid induction agents (eg, etomidate, succinylcholine), reversal agents (eg, naloxone, flumazenil), antihistamine (eg, diphenhydramine), and additional “code drugs” (eg, epinephrine, sodium bicarbonate, calcium chloride, or gluconate). A mobile “code cart” should be kept nearby.¹³

In suspected LAST-related cardiac arrests, immediate access to and administration of 20% intravenous lipid emulsion is a critical modification to the American Heart Association cardiac arrest protocol.¹⁴ ASRA provides a checklist for LAST management (accessible online at https://www.asra.com/content/documents/asra_last_checklist_2018.pdf). An available, preassembled LAST bundle, including the ASRA checklist as a cognitive aid, is recommended.¹⁵

Ultrasound Machine

Ultrasound guidance has become widespread due to its efficacy and safety. Use of ultrasound (US) improves efficiency by decreasing RA performance time and onset time and increasing block success as defined by complete sensory blockade.¹⁶ USG compared to nerve stimulation is associated with fewer vascular and skin punctures¹⁷ and reduced risk of LAST.¹⁸ USG has not been shown to eliminate the risks of RA¹⁹ but may be an important component of safe RA
practices.¹⁰,²⁰ An US machine with probes appropriate for the expected RA practice would be necessary.

RA Equipment

Common block-related materials, which may also be commercially available in customizable block kits, usually includes block needle (20- or 22-gauge blunt tipped), multiple size syringes and needles, additional sterile drapes, sterile US probe sleeve and gel, and skin disinfecting solution. Specific LA and concentration may be selected based on the desired block. A peripheral nerve stimulator may also be available. These preparations and equipment must be readied, and informed consent for RA should be obtained²¹ prior to the performance of any PNB.

Common Blocks

This section will be targeted review of commonly performed USG nerve and fascial plane blocks with in-plane needle techniques and inclusion of select US images. Knowledge of certain emerging blocks and techniques may be limited, but best efforts are made to utilize current information at the time of publishing. Of note, a high-frequency (eg, 4-12 MHz) linear probe or low-frequency (eg, 6-2 MHz) curvilinear probe will be referenced.

Blocks of the Neck

Cervical plexus

Indication: The cervical plexus block (CPB) is indicated for head, neck, distal clavicle, and upper chest wall procedures. Deep CPB are applied in certain chronic pain treatments.²²

Relevant Anatomy: The cervical plexus originates from the C1 to C4 spinal nerves. The C2-C4 anterior rami form the superficial, somatosensory branches (lesser occipital, greater auricular, transverse cervical, and supraclavicular nerves). These terminal nerves travel through the prevertebral fascia then deep cervical fascia to emerge posterior to the sternocleidomastoid muscle (SCM) at the C4 level.²² The C1-C3 nerve roots form the deeper, motor branches (ansa cervicalis), located between the prevertebral fascia and transverse process at the C4 level. The carotid artery and internal jugular vein are located medial to the nerves, deep to the SCM.

Positioning and Approach: The patient should be sitting or semirecumbent and facing contralaterally. A high-frequency linear probe is placed in transverse orientation over the SCM at the C4 level, at the midpoint between the mastoid process and clavicle. The CPB nomenclature is inconsistently used in literature.²² For this text, the superficial CPB refers to the subcutaneous infiltration of the superficial cervical branches, the intermediate CPB refers to the blockade of the superficial cervical branches between the prevertebral fascia and superficial layer of the deep cervical fascia (deep to SCM), and deep CPB refers to the blockade of the deep cervical nerves between the deep layer of the prevertebral fascia and transverse process.

The superficial CPB is often performed as a blind subcutaneous injection at the posterior SCM border at its midpoint at the C4 level. Using USG, the SCM posterior border may be visualized to prevent accidentally deeper injection.²² A volume of 5-10 mL of 0.25% or 0.5% longacting LA (eg, ropivacaine, bupivacaine, levobupivacaine) may be used.The intermediate CPB (Fig. 38.1) targets the posterior cervical space immediately deep to the SCM in a lateral to medial needle direction toward the carotid sheath.²² A volume of 5-10 mL of 0.25% or 0.5% long-acting LA may be used.

The deep CPB (see Fig. 38.1) may be equally efficacious as superficial and intermediate blocks²³ but with higher risk for complications.²⁴ Using the same US view, the needle is
advanced lateral to medial toward the C4 transverse process. A volume of 5-10 mL of 0.25% or 0.5% long-acting LA may be used.

FIGURE 38.1 Intermediate and deep cervical plexus blocks. The target of the intermediate cervical plexus block is the plane deep to the sternocleidomastoid between the superficial layer of the prevertebral fascia and deep cervical fascia (yellow triangles). The deep cervical plexus block target is between the prevertebral fascia and C4 transverse process or at the anterior tubercle (green star) close to the nerve root. SCM, sternocleidomastoid muscle; IJ, internal jugular vein; CA, carotid artery; AT, anterior tubercle of C4 transverse process; C4, C4 nerve root.

Specific Risks and Considerations: Superficial and intermediate CPBs are easily performed and have few complications using USG, but the deep CPB is associated with several risks. The same adverse effects and complications may occur with intermediate CPB depending on the technique used (eg, paracarotid infiltration) and with larger injected volume of LA.²²

Phrenic nerve palsy and hemidiaphragmatic paralysis (HDP)
The phrenic nerve (C3-C5) travels cephalad over the anterior scalene muscle surface deep to the prevertebral fascia. Not all patients develop HDP, possibly from variations in nerve root contribution (ie, higher C5 predominance) or presence of an accessory phrenic nerve.²²
Airway obstruction
Bilateral deep CPBs may cause bilateral HDP, as well as vagal or hypoglossal nerve anesthesia.²² Airway obstruction may also occur with a unilateral deep CPB in the presence of an unknown phrenic, vagal, or hypoglossal paralysis contralaterally.²²
Horner syndrome
Horner syndrome has been reported with all three CPB approaches.²²

Blocks of the Upper Extremity

The brachial plexus innervates the upper extremity and most of the shoulder. It may be blocked at different locations depending on desired target. Additional blocks, such as the CPB and intercostobrachial block, may be combined with a brachial plexus block.

Brachial plexus: interscalene approach

Indication: The interscalene block (ISB) is used for shoulder and upper arm procedures. It may be combined with a CPB for distal clavicle surgery.

Relevant Anatomy: The C5 and C6 nerve roots, and sometimes C7, are targeted between the anterior and middle scalene muscles approximately at the level of the cricoid process.
The US image appears as a three vertically stacked hypoechoic circles (stoplight sign), comprised of the C5, C6, and C7 roots or the C5 and bifid C6 roots,²⁵ between the scalene muscles. Notable structures include the cervical sympathetic chain cranially, vertebral artery deep to the plexus, and internal jugular and carotid sheath anteriorly.

Positioning and Approach: The patient should be placed in a supine or semirecumbent position and facing in the contralateral direction, or a lateral position may be utilized. A high-frequency linear probe should be placed in transverse orientation at the cricoid cartilage level.

The needle should be advanced in a posterior to anterior direction through the middle scalene muscle. Conventionally, the needle pierces the brachial plexus sheath between C5 and C6 (Fig. 38.2). Alternatively, the end point may be anterior to the middle scalene muscle but posterior to the C5 and C6 nerve roots without entering the plexus sheath with similar efficacy and potentially fewer side effects.²⁶ A 15-20 mL volume of 0.5% long-acting LA may be injected.

Specific Risks and Considerations

Phrenic nerve palsy and HDP
Ipsilateral phrenic nerve palsy occurs with nearly 100% incidence²⁷ from LA spread to the cervical roots or by direct phrenic nerve blockade over the anterior scalene muscle. Temporary HDP and reduced pulmonary function occur, with a 30% decrease in forced vital capacity.²⁸ Caution should be exercised in patients intolerant to decreased pulmonary volume or those with contralateral HDP. Low-volume injection (10 mL), proximal digital pressure techniques, and distal injection sites have not demonstrated reliable prevention.²⁸ Suprascapular and axillary blocks (see below) have been proposed as an alternative for shoulder procedures.
Dorsal scapular nerve (DSN) and long thoracic nerve injury (LTN)

The DSN travels within the middle scalene muscle, toward the levator scapulae and rhomboid muscles to pull the scapula medially.²⁹ The LTN also runs within the middle scalene muscle body close to the DSN²⁹ and is responsible for serratus anterior muscle
innervation, which pulls the scapula anteriorly into the thorax. Both nerves may be injured during in-plane ISB and may develop into chronic shoulder pain syndromes.²⁹ DSN syndrome may also have rhomboid and levator scapulae weakness (ie, difficulty pulling scapula medially), while LTN syndrome may display a medial translation and inferior angle rotation toward the midline (ie, winged scapula).²⁹

FIGURE 38.2 Interscalene brachial plexus block. The classic three cervical nerve roots are stacked between the middle and anterior scalene muscles. The needle target may be outside of the brachial plexus sheath (yellow triangle) or within the sheath between C5 and C6 nerve roots. MSM, middle scalene muscle; ASM, anterior scalene muscle; C5, C6, C7, cervical nerve roots; DSN, dorsal scapular nerve; PN, phrenic nerve; VA, vertebral artery.

Cervical plexus blockade
Due to its proximity, LA diffusion to the cervical sympathetic chain and stellate ganglion may produce a benign and reversible Horner syndrome.²²,³⁰ Hoarseness from ipsilateral recurrent laryngeal or superior laryngeal nerve blockade may occur. Emergent airway management may be necessary if a contralateral palsy exists.³⁰

Brachial plexus: supraclavicular approach

Indication: The supraclavicular block (SCB) is used for upper extremity procedures distal to the shoulder. This is not a blockade of the supraclavicular nerve from the cervical plexus. An intercostobrachial block (medial aspect of upper arm) may be added for complete coverage of the upper arm distal to the shoulder or to reduce tourniquet pain.

Relevant Anatomy: The brachial plexus has formed into trunks and divisions at the level of the clavicle. Under US, the plexus appears as a hyperechoic wedge containing multiple hypoechoic circles (a “cluster of grapes”) superolateral to the subclavian artery. The brachial plexus is superficially located as it is superior to the first rib, although anatomic variations exist. The pleura is deep to the first rib, and the dorsal scapular artery may be located within the trunks or branching from the subclavian or transverse cervical arteries.³¹

Positioning and Approach: The patient may be supine or semirecumbent and face toward the contralateral side or in lateral position. A high-frequency linear probe should be placed in the supraclavicular fossa posterior to the clavicle in an oblique coronal direction and directed caudally. Once the brachial plexus is identified lateral to the subclavian artery and superior to the first rib, the needle should be advanced in-plane in a posterolateral to anteromedial direction toward the inner corner pocket of the plexus (7 o’clock of the artery) (Fig. 38.3). Needle tip control should be exercised to avoid passing below the rib or advancing out-of-plane, which may risk pneumothorax. A 20-25 mL volume of 0.5% long-acting LA is commonly injected.

Specific Risks and Considerations: Like the ISB, SCB may cause phrenic nerve palsy causing HDP and Horner syndrome, though at a lower incidence of 34% and 32.1%, respectively.³² Lower injection volume may reduce the incidence of HDP.³³ Historically, SCB was associated with a relatively high incidence of pneumothorax at 6%; however, large studies of USG SCB have reported a lower (up to 0.6 per 1000) incidence of pneumothorax.¹⁹,³⁴

Brachial plexus: infraclavicular approach

Indication: The infraclavicular block (ICB) is used for upper extremity procedures distal to the shoulder. An intercostobrachial block may also be performed to provide medial upper arm coverage or to reduce tourniquet pain.

Relevant Anatomy: The brachial plexus has formed the posterior, lateral, and medial cords around the axillary artery, deep to the pectoralis muscles. The US view of the conventional lateral sagittal approach appears as three hyperechoic structures around the axillary artery, generally at the 7, 11, and 3 o’clock positions, respectively.³⁵ Anatomic variability frequently occurs at this point,³¹,³⁵ including multiple axillary vessels and branches.³⁵

Positioning and Approach: With the conventional lateral (para) sagittal approach, the patient should be supine with the arm abducted 90° and elbow flexed to raise the clavicle,³⁶ while the head is turned contralaterally. Either a high- or low-frequency US probe
is placed longitudinally, inferior to the coracoid process, to capture the short-axis view of the axillary artery deep to the pectoralis muscles. The cords should be visualized around the artery (Fig. 38.4). The needle should be advanced in a cranial to caudal direction, at a steep angulation to the skin, to target the posterior axillary artery at the 6 o’clock position with circumferential spread if utilizing the single-injection technique. Another perivascular injection at the 9 o’clock position may be attempted if employing a double-injection technique. Needle visualization may be difficult due to the depth of the cords (usually 3-6 cm).³⁷ Multiple injections and larger LA volume may be needed as the cords are apart from each other and in variable locations with this approach.³⁷ A volume of 20-30 mL of 0.5% long-acting LA may be injected.

FIGURE 38.3 Supraclavicular brachial plexus block and suprascapular block (anterior approach). The trunks of the brachial plexus at the supraclavicular fossa appears lateral to the subclavian artery. The first rib and pleura are deep to the plexus. The anterior approach to the suprascapular block targets the proximal suprascapular nerve (orange star). BP, brachial plexus; SA, subclavian artery.

The costoclavicular approach is a newer approach.³⁸ The patient may be supine with the arms in neutral position. The linear US probe is placed transverse and slightly oblique on the anterior chest, directly inferior and parallel to the clavicle, with a cephalad tilt toward the costoclavicular space.³⁷ The cords are clustered together in this space at less depth than the lateral sagittal approach,³⁸ lateral to the axillary vessels and deep to the subclavius muscle.³⁷ The needle is advanced lateral to medial to target the costoclavicular space below the subclavius muscle. Needle tip control is important as the arching cephalic vein may travel directly in the needle path and the pleura lies closely inferior to the costoclavicular space.³⁷ As a relatively novel approach, anatomical variants, optimal technique, safety, and efficacy are still being reported. This approach may have a faster block onset than the traditional lateral sagittal approach.³⁹

Another recent technique is the posterior (retroclavicular) approach. The patient may be supine with the arms in neutral position. The US probe position is similar to the lateral sagittal approach, except being 2 cm medial to the coracoid process,⁴⁰ and the US image obtained is like the lateral sagittal view. The needle entry site is superior and posterior to the clavicle and advance in a perpendicular trajectory (although initially under the acoustic shadow of the clavicle) to target the posterior wall of the axillary artery. This avoids the steep angulation needed with the conventional lateral sagittal approach, although a longer needle length may be needed.⁴⁰ More studies are needed to elucidate optimal technique, anatomical variabilities, efficacy, and safety, but early reports suggest similar efficacy compared to the coracoid approach but with more technical ease and better needle visibility due to the perpendicular angulation.⁴¹,⁴²

FIGURE 38.4 Infraclavicular brachial plexus block. The cords are located around the axillary artery deep to the pectoralis muscles. AA, axillary artery; AV, axillary vein; MC, medial cord; LC, lateral cord; PC, posterior cord.

Specific Risks and Considerations: Phrenic nerve palsy and HDP may also occur with the lateral sagittal ICB at a 3% incidence.³² Horner syndrome has an occurrence rate at 3.2%.³² Additional studies are needed to compare risk profiles of the various techniques. At this time, certain approaches may be selected based on patient comfort with positioning.

Brachial plexus: axillary approach

Indication: The axillary brachial plexus block is used for procedures distal to the elbow. This is not a blockade of the axillary nerve (see Shoulder block: suprascapular and axillary). For complete coverage of the anterolateral forearm, a musculocutaneous nerve block may be added.

Relevant Anatomy: The brachial plexus has formed into terminal nerves. The US image appears as three hyperechoic structures around the axillary artery: radial (posteromedial), median (anterolateral), ulnar (anteromedial).⁴³ The musculocutaneous nerve, which travels separately from the other terminal nerves, appears as a hyperechoic structure between the biceps brachii and coracobrachialis muscles, or through the coracobrachialis muscle only. There is anatomic variability in the exact nerve locations and axillary vessels.⁴³

Positioning and Approach: The patient should be supine with the arm abducted 90°, forearm flexed, and shoulder externally rotated to expose the axillary fossa. A high-frequency linear probe should be placed in a sagittal orientation within the axillary fossa to capture a short-axis view of the axillary artery. The radial, median, and ulnar nerves should be visualized around the artery, and the musculocutaneous nerve is between the muscle bellies, posterolateral from the artery (Fig. 38.5). A double-injection technique that separately blocks the musculocutaneous nerve followed by a perivascular injection at the 6 o’clock, 12 o’clock, or both positions of the axillary artery is commonly used. Perivascular injection location or number of injections does not appear to affect efficacy
or onset.⁴⁴ Total volumes of 20-30 mL of 0.5% long-acting LA (5 mL for musculocutaneous) is commonly injected.

FIGURE 38.5 Axillary brachial plexus block. The median, ulnar, and radial nerves surround the axillary artery. The musculocutaneous nerve may be visualized between the biceps brachii and coracobrachialis muscles. AA, axillary artery; AV, axillary vein; MC, musculocutaneous nerve; MN, median nerve; UN, ulnar nerve; RN, radial nerve.

Specific Risks and Considerations: Because the vessels are superficial and easily compressible, this approach may be preferred in anticoagulated patients. Due to the distance from the phrenic nerve and pleura, this approach may be preferred for patients with poor pulmonary reserves.

Shoulder block: suprascapular and axillary

Indication: Combined suprascapular (SSNB) and axillary (ANXB) blocks have been proposed as a diaphragm-sparing alternative to ISB for shoulder procedures in 2007.⁴⁵

Relevant Anatomy: The suprascapular and axillary nerves innervate most, but not all, of the shoulder joint. The suprascapular nerve branches from the superior trunk, which innervates most of the glenohumeral joint and most of the rotator cuff muscles.⁴⁵ Under US, the hyperechoic nerve appears within the suprascapular notch next to the suprascapular artery (posterior approach)⁴⁶ or as the lateral-most aspect of the brachial plexus inferior to the omohyoid muscle at the supraclavicular level (anterior approach).⁴⁷

The axillary nerve is a terminal nerve from the posterior cord, which also innervates much of the glenohumeral joint, some of the rotator cuff (shared innervation of the teres minor tendon), and deltoid muscle.⁴⁵ The hyperechoic nerve may be visualized under US near the posterior circumflex humeral artery on the posterior humerus deep to the deltoid muscle.⁴⁶

Positioning and Approach: For the anterior approach to the SSNB, the patient should be positioned as with the SCB. A high-frequency US probe should be placed in transverse orientation at the C6 level to identify the C5 nerve root.⁴⁷ As the probe moves distally, a hypoechoic nerve will leave the C5 root superior trunk, cross medially deep to the omohyoid muscle, and fuse to the superior trunk at the supraclavicular fossa⁴⁷ (see Fig. 38.3). The SSNB may be targeted at the supraclavicular fossa or as under the omohyoid muscle. Auyong et al. suggests that the anterior approach, using 15 mL of 0.5% ropivacaine, is noninferior to the traditional ISB for arthroscopic shoulder surgery and does not require AXNB.⁴⁸

With the posterior approach to the SSNB, the patient may be positioned sitting,⁴⁵ lateral,⁴⁶ or prone.⁴⁷ The linear US probe should be placed in a transverse oblique orientation in superior to the scapular spine. A cranial tilt should visualize the suprascapular notch deep to the trapezius and supraspinatus muscles. The suprascapular artery and adjacent suprascapular nerve lie within the notch deep to the superior transverse ligament, which bridges the ends of the notch (Fig. 38.6). Injection in the supraspinatus fossa may be
performed deep to the supraspinatus muscle.⁴⁶ A volume of 15 mL of 0.5%-0.75% ropivacaine has been reported.⁴⁵,⁴⁶

FIGURE 38.6 Suprascapular block (posterior approach). The distal suprascapular nerve travels with the suprascapular artery in the suprascapular notch of the scapula. The supraspinatus and trapezius muscles lie superficially. SSN, suprascapular nerve; SSA, suprascapular artery.

The AXNB may be performed in the sitting or lateral positions⁴⁵,⁴⁶ with the shoulder in neutral position, elbow at 90°, and forearm medially rotated (ie, hands in lap). A linear US probe should be placed in the sagittal orientation parallel to the humeral shaft along the dorsal arm and immediately posterolateral to the acromion.⁴⁹ The posterior circumflex humeral artery is the vascular landmark as the axillary nerve is superior to it. In relation to the nerve, the deltoid muscle is superficial, teres minor muscle is cranial, humeral shaft is deep, and triceps muscle lies caudally⁴⁹ (Fig. 38.7). Injections of 8 mL of 20% lidocaine⁴⁹ and 15 mL of 0.5% ropivacaine⁴⁶ have been described.

Specific Risks and Considerations: An early study by Ferré et al. suggests a 40% incidence of HDP with the anterior approach, similarly to SCB and possibly by the same mechanism, while the posterior approach had a 2% incidence.⁵⁰ Additional information regarding anatomy, technique, optimal dosing and volume, and complications is likely to be produced in the future.

FIGURE 38.7 Axillary (nerve) block. The axillary nerve and posterior circumflex humeral artery exit the quadrilateral space, bound by the teres minor superiorly, teres major inferiorly, triceps medially, and humerus laterally, from anterior to posterior to wrap around the humerus posteroanteriorly. The nerve is superior to the artery. PCHA, posterior circumflex humeral artery; AxN, axillary nerve.

Intercostobrachial block

Indication: The intercostobrachial block may be combined with the brachial plexus block to provide more complete upper extremity blockade and may help to reduce tourniquet pain.

Relevant Anatomy: The intercostobrachial nerve originates from the second intercostal nerve, travels through the serratus anterior muscle at the midaxillary line, and into the axilla toward the posteromedial upper arm.

Positioning and Approach: A blind subcutaneous infiltration in an anteroposterior direction along the medial aspect of the upper arm distal to the axilla may be performed. US visualization may be obtained by placing a linear probe at the medial aspect of the upper arm along the humerus below the pectoralis major muscle insertion.⁵¹ Infiltration with 5-10 mL of 0.25% long-acting LA in the anteroposterior direction from the medial upper arm to the inferior border of the triceps muscle.⁵¹

An USG proximal intercostobrachial approach has been described due to insufficient blockade, possibly from anatomical variants. The LA is injected between the pectoralis minor and serratus anterior muscles at the third or fourth rib at the anterior axillary line.⁵¹

Specific Risks and Considerations: Given the proximity to the pleura with the proximal approach, caution should be exercised to avoid causing a pneumothorax.

Blocks of the Trunk: Paravertebral and Paraspinal, Chest Wall, Abdominal Wall

Thoracic paravertebral block

Indication: The thoracic paravertebral block (TPVB) is used for unilateral thoracic or abdominal procedures. It may be used for thoracic analgesia (ie, rib fractures, anginal pain).

Relevant Anatomy: The wedge-shaped paravertebral space (PVS) contains the dorsal and ventral rami of the exiting thoracic spinal nerve and sympathetic chain from that spinal level. At each level, the space is bound by the vertebral bodies and transverse process (TP) medially, parietal pleura anteriorly, and superior costotransverse ligament (CTL) posteriorly. It continues as the intercostal space laterally.⁵² The US image appears as a triangular space lateral to the transverse process between the CTL and pleura in the transverse oblique view or between two adjacent TP deep to the CTL but superficial to the pleura in the parasagittal view (Fig. 38.8).

FIGURE 38.8 Thoracic paravertebral block (transverse approach). The needle target is the paravertebral space, which contain the exiting spinal nerve. The paravertebral space may be visualized lateral to the transverse process and deep to the superior costotransverse ligament. Caution is advised to avoid pleural puncture. CTL, superior costotransverse ligament; PVS, paravertebral space; TP, transverse process.

FIGURE 38.9 Thoracic paravertebral block (sagittal approach) and thoracic erector spinae plane block. The costotransverse ligament houses the paravertebral space, which may be viewed within the acoustic window between the thoracic transverse processes. The erector spinae muscles are posterior to the transverse processes. The needle target for the paravertebral block is the paravertebral space. The needle target for the erector spinae plane block is between the erector spinae muscles and transverse processes. TP, transverse process; CTL, superior costotransverse ligament; PVS, paravertebral space.

Positioning and Approach: The patient may be sitting, prone, or placed lateral. A high-frequency linear probe (or low-frequency curvilinear for deeper views) should be placed in the transverse oblique orientation between adjacent ribs at the desired vertebral level when performing the transverse approach (Fig. 38.9). As the pleura goes deeper into the thorax medially, the CTL may be visualized as a hyperechoic continuation toward the TP. The needle should be advanced in a lateral to medial trajectory and may encounter a “loss of resistance” when entering the target PVS. Injection of 20 mL of 0.5% longacting LA should cause anterior pleural depression.⁵²,⁵³

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