Interscalene block procedure guide

INTRODUCTION — The interscalene block (ISB) anesthetizes the brachial plexus at the level of the nerve roots, and is used for surgery of the upper arm, shoulder, and neck. This topic will discuss the anatomy, ultrasound images, and injection techniques for performing ISB. Clinical applications of this block and other blocks of the brachial plexus are discussed separately. (See "Axillary block procedure guide" and "Infraclavicular brachial plexus block procedure guide" and "Supraclavicular block procedure guide".)

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".)

Ultrasound guidance for peripheral nerve blocks is also discussed in detail separately. (See "Ultrasound for peripheral nerve blocks".)

ANATOMY — The brachial plexus is formed by the ventral rami of the lower cervical and upper thoracic nerve roots (figure 1). It supplies cutaneous and muscular innervation to the upper extremity, with the exception of the trapezius muscle (spinal accessory nerve), the cape of the shoulder (superficial cervical plexus), and a small area of skin near the axilla (intercostobrachial nerve) (figure 1 and figure 2). The ISB targets the ventral rami of C5 and C6 nerve roots which form the superior trunk of the brachial plexus, and usually spreads to C7 (figure 3 and figure 4).

As the name of the block suggests, the C5 and C6 nerve roots can be found in the interscalene groove between the middle and anterior scalene muscles at the level of the sixth cervical vertebra, which is approximately at the level of the cricoid cartilage.

The anterior and middle scalene muscles lie deep to the sternocleidomastoid muscle (SCM) and travel obliquely from the anterior and posterior tubercles of the cervical transverse process to the inner border and scalene tubercle of the first rib, respectively. The fascia surrounding each of the scalene muscles is derived from prevertebral fascia, which splits to invest each muscle and fuses again at their lateral borders, creating an interscalene space. As the nerve roots descend between the two scalene muscles, they travel superior and posterior to the subclavian artery and form the superior (C5 and C6), middle (C7), and inferior (C8 and T1) trunks of the brachial plexus (figure 5).

The phrenic nerve runs vertically down the anterior surface of the anterior scalene muscle at the level of C6. The superficial branches of cervical plexus (C1 to C4) run along the posterior border of the SCM.

●Innervation of the shoulder – The shoulder joint (glenohumeral joint) is innervated by articular branches of the suprascapular, axillary, subscapular, lateral pectoral, and musculocutaneous nerves, all of which originate from C5 and 6 [1]. Articular branches of the subscapular, lateral pectoral, and musculocutaneous nerves innervate the anterior joint, whereas branches of the suprascapular nerve innervate the posterior joint and branches of the axillary nerve innervates the inferior aspect of the joint. Articular branches of the lateral pectoral nerve travel to the clavicle, acromion joint, and subacromial bursa (figure 6).

Cutaneous innervation for the majority of the shoulder is provided by the supraclavicular branches of cervical plexus which arise from C3 to C4 and provide "cape-like" cutaneous innervation to shoulder, and the axillary nerve which covers the lateral-posterior portion of the shoulder (figure 7).

Innervation of the muscles of the shoulder is as follows [2]:

•The axillary nerve innervates the deltoid and teres minor muscles

•The subscapular nerve innervates the subscapularis muscle

•The suprascapular nerve provides motor innervation to the supraspinatus and infraspinatus muscles

•Lateral pectoral nerve innervates the pectoralis major, with occasional branches to the deltoid

●Vascular structures – Vascular structures that must be avoided during needle placement include:

•The external jugular vein, which often overlies the interscalene groove at the level of C6.

•The vertebral artery, which ascends from the subclavian artery in the transverse foramina of the cervical vertebrae and anterior to the cervical nerve roots, deep to the anterior scalene muscle.

•The carotid artery and the internal jugular vein lie anteromedial to the anterior scalene muscle.

•The transverse cervical artery leaves the thyrocervical trunk and passes transversely below the inferior belly of the omohyoid muscle to the anterior margin of the trapezius (figure 8).

Clinical implications of anatomy — The ISB usually anesthetizes the C5 to C7 nerve roots (superior and middle trunks of the brachial plexus), as well as the supraclavicular branches of the cervical plexus (C1 to C3) [3,4]. Thus, the ISB is a reliable anesthetic for shoulder surgery (eg, shoulder arthroscopy, replacement, relocation, or rotator cuff repair), with reported success rates over 90 percent, 99 percent with ultrasound guidance [5]. ISB is also used for distal clavicle surgery. ISB is not used for surgery distal to the midhumerus (ie, elbow or hand surgery), as the block often spares the lower trunk of the brachial plexus (C8 and T1) (figure 2).

ISB using typical volumes of local anesthetic (LA) spreads to the phrenic nerve, which arises from the C3 to 5 nerve roots and courses distally along the anterior surface of the anterior scalene muscle. ISB with the typical approach and local anesthetic volumes results in phrenic nerve block and hemidiaphragmatic paralysis [6,7]. Thus, ISB should be avoided in patients with certain conditions such as contralateral hemidiaphragmatic paresis or moderate to severe pulmonary disease. (See 'Phrenic nerve block' below.)

Phrenic block is associated with an approximately 25 to 30 percent reduction in forced expiratory volume in one second (FEV₁) and forced vital capacity (and possibly more in patients with obesity) [8] and may not be tolerated by patients with limited pulmonary reserve. The use of a lower volume of LA may reduce the incidence of phrenic nerve palsy [9,10], but the quality and distribution of the block may suffer, and phrenic block cannot be predictably avoided.

SINGLE INJECTION INTERSCALENE BLOCK

Ultrasound guidance versus nerve stimulation guidance — We use ultrasound guidance to perform ISB. When ultrasound is not available, nerve stimulation is a reasonable alternative.

●Ultrasound-guided ISBs have been shown to produce improved sensory and motor blockade compared to stimulation guided techniques [5].

●Ultrasound-guided blocks result in fewer needle passes and faster onset of motor blockade compared to stimulation-guided ISBs [11].

●Ultrasound-guided ISB results in improved success rates for surgical anesthesia compared with nerve stimulation guidance (99 versus 91 percent) and fewer conversions to general anesthesia [5]. However, when the ISB is used for postoperative analgesia, termination of sensory and motor blockade are similar between the two techniques [12].

●Lower volumes of local anesthetic (LA) are required for successful blockade with ultrasound guidance versus stimulation [13].

●Total block time, patient satisfaction, and postoperative neurologic complications are similar with ultrasound guidance and nerve stimulator-guided ISB [11].

Some of the benefits of ultrasound guidance are likely explained by the ability to directly visualize the needle tip with ultrasound, and to confirm appropriate spread of LA in real time. Needle adjustments can be easily made if LA distribution around the brachial plexus is considered inadequate.

Nerve stimulation guidance along with ultrasound guidance — Some practitioners prefer to use nerve stimulation concurrently with ultrasound guidance. We do not routinely use both guidance techniques, but occasionally use nerve stimulation to confirm needle tip placement when performing an ultrasound-guided ISB if the ultrasound image is unclear or difficult to obtain (eg, in patients with obesity or when positioning is difficult).

In a randomized trial that compared ultrasound guidance, nerve stimulator guidance, and ultrasound-guided/nerve stimulator-confirmed ISB for postoperative analgesia in 106 patients who underwent shoulder arthroscopy, quality of the block, and block duration were similar among groups. [12].

Ultrasound-guided technique

●Patient preparation before peripheral nerve block is discussed separately. (See "Overview of peripheral nerve blocks", section on 'Patient preparation'.)

●Select a linear high frequency transducer (eg, 15-5 mHz) (picture 1). (See "Ultrasound for peripheral nerve blocks", section on 'Transducers'.)

●Place the patient in the supine or semi upright position with the head turned 45 degrees to the opposite side. Alternatively, the patient can be positioned in the lateral decubitus position with the patient facing away from the proceduralist.

●Using sterile technique, place the transducer in the supraclavicular fossa, in an orientation transverse to the neck. (picture 2)

●Identify the subclavian artery and the divisions of the brachial plexus lateral to the artery. The brachial plexus will appear as hypoechoic circular structures that are often described as a "bundle of grapes."

●With the brachial plexus centered on the ultrasound screen, move the transducer cephalad to the level of the cricoid cartilage (C6). As the transducer is moved cephalad, the brachial plexus will become more compact as divisions become trunks; the superior trunk will be visualized as the anterior and middle scalene muscles come into view (image 1 and image 2).

●The C5 and 6 roots appear as hypoechoic round structures, in a vertical orientation with C5 most superficial, C6 deep to it, and C7 deepest. C6 often splits, and the resulting three images (C5, and two portions of C6) comprise what is often referred to as the stoplight sign (image 3 and image 4) [14]. The roots are typically visualized at a depth between one and three cm. C5 is often smaller in size than C6 and C7 and rarely splits.

●Use color Doppler to confirm that visualized structures are nerves rather than blood vessels (image 5 and movie 1). Anatomic variations have been documented, with vascular structures appearing as nerve roots [15].

●Insert a short bevel 5 cm 22 gauge needle using an in-plane or out-of-plane ultrasound approach (picture 3). Advance the needle tip to a position between the C5 and C6 nerve roots (image 6). A pop may be felt as the needle tip passes through the prevertebral fascia surrounding the brachial plexus (movie 2).

●Nerve stimulation can be used to confirm needle tip placement. (See 'Nerve stimulation guided technique' below.)

●After negative aspiration, inject 10 to 30 mL of LA in 5 mL increments, with gentle aspiration between injections, while visualizing spread of LA around the nerve roots (image 7 and image 6 and movie 3) (see 'Drug choices and dosing' below). Stop injection and reposition the needle tip if the patient complains of pain or paresthesia, if injection of local anesthetic is not visualized or if there is resistance to injection. Avoid high injection pressure. If using an injection pressure monitoring device, limit injection pressure to <15 pounds per square inch.

The following structures are not routinely identified during every block; however, it is important to be familiar with their location and sonographic appearance to avoid needle contact.

●The great vessels (internal jugular vein and carotid artery) can be found medial to the anterior scalene at the level of C5 to C7.

●The phrenic nerve can be visualized on the anterior surface of the anterior scalene muscle.

●The superficial cervical plexus can be visualized at the posterior border of the sternocleidomastoid.

●The vertebral artery and vein can be visualized deep to the anterior scalene muscle at the C7 level and may be best identified using color doppler.

●The transverse processes for C5, C6, and C7 can be visualized posterior and deep to the brachial plexus. The C7 transverse process is the most frequently visualized transverse process at the level of block placement and is easily identified by its large posterior tubercle just posterior to the C7 nerve root. Scanning cephalad, the C5 and C6 transverse processes can be identified with both anterior and posterior tubercles visualized in a "horseshoe" shape around their respective nerve root.

Nerve stimulation guided technique

●Place the patient in the supine or semi-upright position with the head turned to the opposite side.

●Palpate the posterior border of the clavicular head of the sternocleidomastoid muscle (SCM) and the cricoid cartilage (picture 4). Having the patient lift the head off the table while facing away tenses the SCM, and may make the border of the muscle easier to identify (picture 5).

●Palpate the anterior and middle scalene muscles, posterior to the SCM. Gently roll fingertips between the muscles to identify the interscalene groove.

●Insert a short bevel 5 cm 22 gauge needle perpendicularly to the skin, in the interscalene groove, at the level of the cricoid cartilage.

●Using nerve stimulation starting at 1 mA, advance the needle in a slightly caudad and posterior orientation until a muscle response occurs at the deltoid, biceps, triceps, or pectoralis muscles.

●If muscle twitch occurs of the trapezius, rhomboid, or serratus anterior muscles, the needle is positioned too posterior and lateral to the middle scalene muscle, and is stimulating the accessory, dorsal scapular, or long thoracic nerves, respectively. If the patient develops hiccups during needle stimulation, the needle is positioned too anteriorly and is causing diaphragmatic contraction via phrenic nerve stimulation. In either case, reposition the needle tip.

●After a motor response is achieved at 1 mA, reduce the stimulation intensity. If a muscle response is still observed at <0.2 mA, withdraw the needle slightly as this may indicate intraneural needle placement. Withdraw the needle to a point at which a motor response is maintained at approximately 0.4 mA but abolished at lower intensity.

●After negative aspiration, inject 10 to 30 mL of LA in 5 mL increments, with gentle aspiration between injections (see 'Drug choices and dosing' below). Stop injection and reposition the needle tip if the patient complains of pain or paresthesia, or if there is resistance to injection. Avoid high injection pressure. If using an injection pressure monitoring device, limit injection pressure to <15 pounds per square inch.

DRUG CHOICES 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 1). LAs for peripheral nerve blocks, including use of adjuvants, are discussed in more detail separately. (See "Overview of peripheral nerve blocks", section on 'Drugs'.)

Choice of local anesthetic — Choices of LA for ISB 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 onset and duration that are both intermediate between the two agents [16].

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

Liposomal bupivacaine — We do not routinely use liposomal bupivacaine for peripheral nerve block. In 2018 liposomal bupivacaine was approved by the US Food and Drug Administration (FDA) for ISB for postsurgical pain. The approval was based on a study that found improved analgesia for 48 hours postoperatively in patients who received liposomal bupivacaine, compared with placebo [17]. However, a 2019 meta-analysis of seven randomized trials that compared liposomal bupivacaine with plain bupivacaine or ropivacaine for ISB for major shoulder surgery found similar postoperative pain scores, opioid consumption, and adverse effects in both groups [18]. Similarly, in a 2022 randomized trial of 112 patients who underwent shoulder surgery with interscalene blocks, postoperative analgesia and opioid consumption were similar in patients whose blocks were performed with standard bupivacaine with perineural dexamethasone versus liposomal bupivacaine. [19]. Thus, further studies are required before recommending the routine use of liposomal bupivacaine for ISB.

Liposomal bupivacaine should be used with caution in patients with decreased respiratory function given the potential for prolonged phrenic nerve blockade.

Volume of local anesthetic solution — The volume of LA solution used for ISB can affect the efficacy of the block, and the incidence of phrenic nerve block. Low volumes of LA for ISB reduce the incidence of phrenic nerve block, but may also reduce the quality of the block due to impaired distribution of the LA [20,21]. (See 'Phrenic nerve block' below.)

●For ultrasound-guided block, a minimum of 10 mL of LA is required to avoid a high block failure rate [20,21]. For nerve stimulator-guided ISB, higher volumes are required (ie, 15 to 30 mL).

●The use of a lower volume of LA solution for ISB (5 mL) is associated with a lower incidence of phrenic nerve block. However, the vast majority of patients with phrenic nerve block have few to no symptoms and require no treatment [9,10,22].

CONTINUOUS INTERSCALENE BLOCK — Continuous ISB can be used to prolonged analgesia beyond the duration of a single-shot block (table 1). Prolonged analgesia may be desirable after shoulder surgery, particularly for major surgery, which results in moderate to severe pain for many patients. A meta-analysis of 15 small randomized or quasi-randomized trials that compared continuous versus single-shot ISB for major shoulder procedures found that continuous block reduced cumulative postoperative morphine consumption and dynamic and resting pain scores up to 48 hours, without an increase in complications [23].

Catheter placement technique — The technique for catheter placement is similar to the technique used for single-shot injections using ultrasound guidance or nerve stimulation. A 19 or 20 gauge Tuohy needle is placed, rather than a block needle. Stimulating Tuohy needles are available. A single- or multi-orifice catheter is inserted through the needle, and advanced far enough to allow the catheter perforations to bathe the nerves, typically with 4 to 6 cm of catheter left in place.

Catheter-over-needle kits are available for perineural catheter placement, including stimulating needle kits. Needle placement is the same as for a Touhy needle, but the catheter slides over the end of the needle, similar to intravenous (IV) catheter placement.

We use ultrasound guidance for perineural catheter placement for ISB. We inject several mL of local anesthetic (LA) through the needle under ultrasound guidance to confirm correct placement of the needle tip, visualize insertion of the catheter, and then inject the rest of the bolus through the catheter in divided doses, while visualizing spread of LA. Importantly, if a perineural catheter is placed using nerve stimulation only, a test dose (1.5% lidocaine with epinephrine [5 mcg/mL]) should be injected through the catheter to confirm that the catheter tip is not intravascular, epidural, or intrathecal, before injecting the block drug solution [24].

Positioning, draping, and securing the catheter — There are several technical aspects to consider when placing a catheter for continuous ISB.

●Placement of a perineural catheter takes longer than a single injection block and sufficient time must be allocated prior to surgery (generally 30 to 45 minutes).

●A large sterile field should be created to avoid contamination of the catheter. Either sterile towels or a clear plastic drape can be used. A clear plastic drape may facilitate communication with the patient and is more comfortable for patients with claustrophobia. For patient positioning, a semi-upright or lateral decubitus position may be used. The lateral decubitus position may be easier for the patient and allows for better access to tunnel and secure the catheter (picture 6 and picture 7).

●In addition to sterile gloves, mask, and cap, we wear a sterile gown to avoid contamination of the catheter during placement. A sterile ultrasound sheath must be used to avoid contamination of the sterile field.

●More liberal LA is usually required at the needle insertion site, since a larger needle is used. Slightly heavier sedation may also be necessary, though the patient needs to be conscious enough to report a paresthesia or pain on injection.

●The skin of the neck is highly mobile, so the catheter must be secured well to avoid catheter migration and/or inadvertent removal. We use a surgical glue at the catheter insertion site and loop the catheter under clear plastic sterile dressings to allow for slack if the catheter is inadvertently pulled.

●The catheter must be taped away from the surgical field, which can be challenging for shoulder arthroplasty and arthroscopy. We tunnel catheters posteriorly and sometimes tape the catheter from that point, behind the neck and to the other shoulder, where the pump tubing can be connected. At the end of surgery, the surgical drapes should be removed cautiously to avoid having the catheter and catheter dressing inadvertently removed.

Infusion drug dose — After injecting a bolus of LA as described above for single injection block, we start an infusion of LA at 5 to 12 mL/hour postoperatively, with either continuous infusion or programmed intermittent bolus with the same volume programmed to bolus once per hour. Our practice is as follows:

●For ambulatory patients with home-going catheters, we use a continuous infusion of 0.2% ropivacaine. Prior to discharge, the patient receives a comprehensive instruction sheet that includes the signs and symptoms of LA toxicity, pump maintenance information, and the acute pain service phone number for any issues that may arise.

●For inpatients, we use 0.2% ropivacaine; others use 0.1% bupivacaine.

COMPLICATIONS — Interscalene nerve blocks (ISBs) are generally very safe. 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'). Several complications are more likely with ISB than with many other peripheral nerve blocks.

Phrenic nerve block — ISBs using typical volumes of LA (10 to 30 mL) result in phrenic nerve blockade and resultant hemidiaphragmatic paralysis, with an incidence near 100 percent [6,8]. Hemidiaphragmatic paralysis results in a decrease in forced expiratory volume in one second (FEV₁) and forced vital capacity in nonobese patients by approximately 25 to 30 percent [25] and even more significant decreases in patients with obesity [8]. Such changes may be poorly tolerated in patients with reduced pulmonary reserve. Even low-volume ISBs (5 mL) result in hemidiaphragmatic paralysis with an incidence of approximately 45 percent [9].

Alternative approaches to reduce the incidence of phrenic nerve blockade with ISB include low volume ISB and LA deposition lateral to the interscalene groove (extrafascial block) [9,22]. These approaches could be considered in patients with pulmonary disease or obstructive sleep apnea, but may result in a higher risk of block failure or impaired distribution of LA [20,21]. In patients with severe pulmonary comorbidities who may be less likely to tolerate any degree of phrenic nerve blockade, avoiding ISB may be prudent. Alternatives to ISB, including superior trunk block, suprascapular nerve block, or axillary nerve block may be considered in these patients. For patients in whom we want to avoid phrenic nerve block, for shoulder surgery we perform both an ultrasound-guided anterior suprascapular nerve block and an infraclavicular nerve block to provide analgesic coverage of the suprascapular and axillary nerves, respectively. (See "Upper extremity nerve blocks: Techniques", section on 'Suprascapular nerve block' and "Infraclavicular brachial plexus block procedure guide".)

The duration of phrenic nerve blockade is typically determined by the duration of the LA effect, which is related to the type and mass of the LA used. Despite the high incidence of phrenic nerve blockade, patients typically exhibit few to no symptoms and require no specific treatment after a single injection technique [9,22]. However, a single institution retrospective review of patients undergoing continuous ISB technique for shoulder arthroplasty found a high incidence of respiratory complications with prolonged phrenic nerve blockade and identified patient risk factors [26]. Very few patients with chronic obstructive pulmonary disease, interstitial lung disease, or pulmonary hypertension received ISB. Among the 1025 cases studied, 27 percent required some oxygen supplementation and 6 percent required chest imaging. Patient-related risk factors for respiratory complications included American Society of Anesthesiologists physical status of 3 (versus 1 or 2), advanced age, asthma, congestive heart failure, higher body mass index, and lower preoperative oxygen saturation. Although a direct causal relationship cannot be proven with a retrospective analysis, additional considerations should be given to patients with these risk factors for respiratory complications prior to performing a continuous ISB.

Other — Other complications and side effects that may occur due to ISB include:

●Horner's syndrome: Due to transient blockade of the sympathetic trunk [27,28].

●Hoarseness: Due to transient blockade of the recurrent laryngeal nerve [27].

●Rarely reported complications of ISB include long term phrenic nerve palsy [29,30], dorsal scapular or long thoracic nerve injury [31], pneumothorax [32], epidural injection [33,34], and intrathecal injection with total spinal anesthesia [35].

SUMMARY AND RECOMMENDATIONS

●Anatomy

•The interscalene block (ISB) targets the interscalene groove between the anterior and middle scalene muscles at the level of the sixth cervical vertebra. (See 'Anatomy' above.)

•The ISB usually anesthetizes the C5 to C6 nerve roots, as well as the supraclavicular branches of the cervical plexus (C1 to C3), and usually spreads to block C7 (figure 3).

•The ISB is a reliable block for shoulder surgery and distal clavicle surgery. (See 'Clinical implications of anatomy' above.)

●Ultrasound versus nerve stimulation guidance – We use ultrasound guidance for ISB, and occasionally use nerve stimulation to confirm the needle tip location if the ultrasound image is unclear or difficult to obtain. Ultrasound guidance improves the quality of ISB for surgical anesthesia compared with nerve stimulation guidance, but there is similar quality and duration of postoperative analgesia. (See 'Ultrasound guidance versus nerve stimulation guidance' above.)

●Ultrasound-guided single injection ISB – We perform ultrasound-guided ISB as follows, with further explanation above (see 'Ultrasound-guided technique' above):

•Use a linear high frequency transducer (picture 1).

•Position the patient semi-upright with the head turned 45 degrees to the opposite side.

•Begin scanning in the supraclavicular fossa to identify the brachial plexus (picture 2 and image 1 and image 2).

•Scan cephalad, following the brachial plexus to the level of C6 (image 2) and identify the C5 and 6 nerve roots (image 4).

•Use color Doppler to identify and avoid blood vessels (image 5 and movie 1).

•Insert a 20 to 22 gauge block needle from lateral to medial with the needle advanced between the C5 and 6 nerve roots (image 6 and movie 2).

•After negative aspiration, inject 10 to 30 mL of local anesthetic (LA), in 5 mL increments, with gentle aspiration between injections, while visualizing spread of LA around the nerve roots (image 6 and movie 3).

●Nerve stimulation-guided single injection ISB – Further detail is provided above. (See 'Nerve stimulation guidance along with ultrasound guidance' above.)

•Position the patient supine or semi-upright with the head turned to the opposite side.

•Identify the interscalene groove between the anterior and middle scalene muscles at the level of C6 (picture 5).

•Insert a short bevel 5 cm 22 gauge needle perpendicularly to the skin.

•Turn on stimulation at 1 mA and advance in a slightly caudad and posterior direction until muscle response occurs at the deltoid, biceps, triceps, or pectoralis muscles.

•Reduce stimulation and withdraw the needle to the point at which motor response is maintained at 0.4 mA but abolished at lower intensity.

•After negative aspiration, inject 10 to 30 mL of LA, in 5 mL increments, with gentle aspiration between injections.

●Continuous ISB technique – Continuous ISB is performed as described for single injection block, using a Touhy needle with a 19 or 20 gauge catheter inserted through it, 4 to 6 cm into the adductor canal. (See 'Continuous interscalene block' above.)

●Local anesthetic choice (see 'Local anesthetics' above and 'Infusion drug dose' above):

•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)

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

-For continuous ISB  Bolus as for single injection ISB, followed by infusion of 0.2% ropivacaine for ambulatory patients, 0.2% ropivacaine or 0.1% bupivacaine for inpatients

●Side effects and complications (see 'Complications' above)

•Phrenic nerve block – ISB is associated with a near 100 percent incidence of phrenic nerve block at LA volumes that produce an effective block. Phrenic nerve block may be poorly tolerated in patients with significant pulmonary compromise; alternative blocks should be considered. (See 'Phrenic nerve block' above.)

•Others – Other possible side effects and complications of ISB include Horner's syndrome, hoarseness, and rarely, long term phrenic nerve palsy, nerve injury, pneumothorax, and epidural or intrathecal injection. (See 'Other' above.)