Introduction: Continuous interscalene nerve block is arguably the most effective of all the continuous techniques: a single catheter can block the entire surgical field; shoulder surgery can be painful for 72 or more hours, and motor block related to interscalene block is well tolerated.
Skill level: advanced: mainly due to the difficulty securing an interscalene catheter in a challenging area of the body.
Procedure time: 10-15 mins (10 mins for experienced practitioners)
Strong – Rotator cuff repair (arthroscopic and open), total shoulder replacement
Moderate – Arthroscopic subacromial decompression (acromioplasty), excision lateral clavicle (“Mumford procedure”), athroscopic stabilisation (including “SLAP” lesion, labral tears)
Sedation: e.g. midazolam 2 mg + alfentanil 250-500 mcg
Anatomy: Ultrasound guided interscalene block is performed at the root/trunk level of the brachial plexus (approx. C6/7 vertebral level, corresponding to the cricoid cartilage level). At this level, the roots/trunks lie wedged between the scalene muscles (Fig. 1). Significant variability exists in their position and visibility (1-4 roots/1-3 trunks may be visible). The interscalene roots/trunks appear hypoechoic compared to the surrounding scalene muscles (Fig. 2). The superficial-most scalene muscle fascia often appears as a “flying seagull sign”: the most superficial root represents the bird’s trunk; the scalene fascia appearing as its wings. Aim to place the interscalene block LA/catheter directly lateral to the two most superficial structures = C5/6 or superior/middle trunks which innervate the shoulder area.
The phrenic nerve lies on the surface of the anterior scalene muscle, while the long thoracic and dorsal scapula nerves lie approx. 0.7 cm lateral (posterior) to the C6 root, which itself lis approx. 1 cm deep to the skin. Contact with all three nerves during interscalene block is best avoided by use of an "anterolateral" needle approach (see below).
Fig. 1. Interscalane nerve block: illustration of the roots/trunks at the C6/7 vertebral level lying in between the anterior and middle scalene muscles. At the immediate supraclavicular level, the trunks/divisions are closely grouped superolateral (and posterolateral) to the subclavian artery.
Fig. 2. Ultrasound image of right interscalene area for ultrasound guided interscalene block. SCM=sternomastoid muscle. ASM=anterior scalene muscle. MSM=middle scalene muscle. PSM=posterior scalene muscle. C5/6=5th / 6th cervical nerve roots
Surface landmarks: mark out:
(2) Posterior border of sternomastoid muscle from mastoid process to clavicle (accentuate by asking patient to lift their head off the pillow with your hand pressed against their forehead).
(3) Level of the cricoid cartilage on line “2” (= approximately C6).
(4) Midpoint of line 2 distance between mastoid and level of cricoid (Fig. 3). Also a good idea to mark out the external jugular vein to help avoiding subsequent needle puncture, which can cause problematic bleeding.
Fig. 3. Landmarks for both modified superficial cervical plexus block and interscalene catheter placement.
Needle: 4-5 cm (depending on patient weight: usually 4 cm; > 100 kg = 5 cm) stimulating 18G Tuohy needle with multi-orifice catheter.
1. High resolution (10-15 MHz) linear probe e.g. Sonosite L38
2. 4-5 cm Tuohy needle catheter kit with catheter cut using a surgical blade to approximately 20-25 cm (cutting the catheter will make catheter placement less fiddly and will improve patient acceptance).
3. Medical cyanoacrylate (e.g. dermabond 0.5 mL vial)
4. Catheter anchoring device (e.g. Lockit)
5. Tincture of benzoin (Friar’s balsam)
6. Surgical blade (to cut catheter)
Procedure (Video 1, 2, 3)
2. First perform “modified” superficial cervical plexus block (Video 1). With a 22G blunt needle, bent to 30 degrees at its midpoint, infiltrate 5 mL LA 1 cm posterior to the posterior border of sternomastoid at the midpoint between the C6 level and mastoid process. Subcutaneously infiltrate a further 2.5 mL along the posterior border of sternomastoid between the aforementioned point and the C6 level (Fig. 4). Infiltrate a further 2.5 mL along a similar line 30 degrees posterior to the sternomastoid posteror border. This block will anesthetise the skin to be penetrated by the catheter needle and the skin of the shoulder (via the supraclavicular nerves).
Fig. 4. Modified superficial cervical plexus block. Infiltration along posterior border of sternomastoid muscle between: 1. Midpoint between C6 level and mastoid process, and 2. The C6 level.
3. Next place the interscalene catheter with patient supine and head turned to the contralateral side:
4. Needle entry point is approximately 3cm cephalad of the C6 level just posterior to the posterior border of the sternomastoid. Avoid puncturing the external jugular vein.
5. Set nerve stimulator to 0.8-1 mA, pulse width 0.1 ms and 2 Hz
6. Gently place probe on neck at the C6/C7 vertebral level (=cricoid level) and visualise the 1-2 most superficial elements of the brachial plexus (Fig. 2). Probe orientation is in the axial plane and angled slightly towards the ipsilateral shoulder ("axial-oblique"; Fig. 5). It is useful to picture in one's mind the probable direction of the plexus as the probe needs to be perpendicular to it (Fig. 1). The roots appear hypoechoic between the surrounding hyperechoic scalene muscles. The medially located carotid artery and internal jugular vein represent a convenient initial landmark. Once visualised, move the probe 2-3 cm laterally: the roots are usually 2-3 cm lateral to the great vessels at approximately the same depth.
7. With a 10 ml dextrose filled syringe attached directly to the Tuohy needle, advance needle until tissue displacement is observed just lateral to the most superficial brachial plexus root/trunk but superficial to the middle scalene muscle fascia (Fig. 5).
Fig. 5. Interscalene catheter insertion (left). Needle-probe orientation.
8. Penetrate fascia overlying the middle scalene muscle (always associated with a “pop” when using an 18G Tuohy needle – requires a short, sharp deliberate needle movement once the needle tip is against the fascia) (Video 3).
9. Angle needle tip medially until appropriate root/trunk medial movement observed and preferably also a deltoid (anterior shoulder movement), biceps or triceps motor response.
10. Inject 10 mL dextrose 5% aiming to observe hypoechoic injectate spread immediately lateral/under the most superficial root/trunk. With this needle alignment and an 18G Tuohy tip, intraneural needle placement is probably impossible, so aim to get needle tip/injectate spread as close as possible to the target root/trunk.
11. Drop the probe, stabilise this needle position by transferring the hand previously holding the probe to the needle hub. Disconnect syringe and advance the catheter with the pink catheter advancing piece sited within needle hub. Advance catheter at least 5 cm beyond needle tip.
12. Withdraw needle over catheter and immediately stabilise catheter by pressing catheter against skin with finger at skin entry point.
13. Withdraw catheter to 3 cm beyond needle tip. Be very careful during the last cm of catheter withdrawal as the catheter can have a tendancy to spontaneously dislocate at this point.
14. Carefully apply medical cyanoacrylate (e.g. dermabond) to skin entry site (aids secural and minimises LA leakage)
15. Apply tincture of benzoin or "Skin-Prep" to 2 cm radius of skin around catheter puncture site (improves Lockit-skin adhesion).
16. Apply Lockit catheter fixation device
17. Protect catheter from surgical drapes using small gauze and paper tape.
18. Dress catheter after surgery as described in catheter fixation.
Local anesthetic regimen: Bolus 20 mL local via catheter e.g ropivacaine 0.375% then postoperative infusion regimen 2-5 mL/hr + PRN 5-10 mL boluses e.g ropivacaine 0.2% (e.g. PainBuster elastomeric pump)
1. Central Neuraxial Needle Placement/Injection. This is the most significant potential complication to always be wary.
a) Needle depth: The needle tip should not penetrate > half the distance from the skin to the vertebral column (< 1.25 cm in most, but certainly < 2.5 cm). The maximum safe needle depth can be estimated by calculating 25% of the lateral neck width.
b) Needle orientation: Maintaining a needle orientation dorsal and caudad will minimise the risk of penetrating an intervertebral foramen in the event that the needle encroaches on the vertebral column.
Catheter should not be left > 3-4 cm beyond the needle tip.
2. Intraneural injection: Possible when using a fine (22g or finer) needle orientated perpendicular to the roots/trunks. Follow the general advice described under complications.
The risk of the above complications is markedly reduced by using an 18G Tuohy needle orientated anterolaterally, as both intraneural needle placement and intervertebral foramen penetration are virtually impossible when using such a needle with this orientation.
3. Pneumothorax. Exceedingly unlikely when the needle tip is kept "lateral" and cephalad of the clavicle.
4. Trauma to the long thoracic, dorsal scapular and phrenic nerves (very unlikely with the anterolateral approach described above).
1. If sonographic visualisation of appropriate roots/trunks proves difficult (3-5% of patients even in experienced hands), first scan distally/caudally to locate the supraclavicular brachial plexus (hyperechoic appearance superolateral to the subclavian artery), then retrace proximally to locate the diverging hypoechoic roots/trunks within the scalene muscles. This is sometimes referred to as the "traceback method" (Video 5). If imaging is still difficult, use ultrasound to approximate the needle tip position (approximately 2-3 cm lateral to carotid artery), drop the probe, and then aim for a sustained deltoid/biceps/triceps/pectoralis motor response at between 0.2-0.5 mA.
2. If the catheter won’t advance past the needle tip, the single most effective manoeuvre is to withdraw the needle tip slightly (< 0.5 cm) while continuously attempting catheter advancement. This will work in 90% of cases. If this fails, try injecting a further 10 mls of injectate through the needle prior to readvancing the catheter. In a small proportion of patients, the catheter simply won’t advance despite the aforementioned manoeuvres. Withdraw the needle and try another needle puncture point.
3. If inadvertent external jugular vein puncture occurs, apply 1-2 vials of medical cyanoacrylate. This is particularly effective for stopping skin bleeding.
4. For SS interscalene block, consider using the in-plane technique approaching from behind/lateral (Fig. 6,7).
Fig. 6. Image of in-plane approach from behind/lateral: an alternative approach for the SS interscalene nerve block technique.
Fig. 7. Image of in-plane approach from behind/lateral for utrasound guided interscalene block. N.B. Extreme caution should be exercised to ensure the needle tip does not encroach on the vertebral column, as the needle orientation is set up for intervertebral foramen penetration and possible intracordal needle placement.
5. The long thoracic and dorsal scapular nerves lie approx. 1 cm deep to the skin and 0.7 cm lateral (posterior) to the plexus, directly in the path of a needle advanced from posterior. Contact with the nerves is unlikely when using the antrolateral approach.
Video 1. Modified superficial cervical plexus block. Note the bent needle, which facilitates a shallow needle path (subcutaneously) towards the clavicle.
Video 2. Left sided interscalene catheter placement.
Video 3. (Right) US clip of interscalene area and appropriate needle induced tissue displacement / injectate spread.
Video 4. Left sided interscalene catheter insertion.
Video 5. Trace back technique for location of the interscalene brachial plexus for interscalene nerve block. "Trace back" refers to identifying the supraclavicular brachial plexus (divisions) then tracing it back to the interscalene roots/trunks.