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Anatomy
Clinically Relevant Information
The brachial plexus is commonly blocked at interscalene level for surgeries involving the clavicle, shoulder and upper arm.
Surgery of the shoulder requires blockade of the supraclavicular (C4) and axillary nerves (C5) for cutaneous analgesia, along with the suprascapular (and axillary) for joint innervation. The supraclavicular nerve comes from the cervical plexus, which is commonly blocked during an interscalene block due to superficial spread.
Surgical anaesthesia can be achieved using suitable strength local anaesthetics, and we commonly perform simple shoulder arthroscopies either awake or lightly sedated.
Do not expect to block the entire brachial plexus using the interscalene approach, as the lower trunks will be missed leading to sparing of predominantly the medial cutaneous supply of the arm (median and ulnar).
Sonoanatomy
Use a high frequency, linear probe for this block. Position the patient slightly head up, with the head rotated away from the side to be blocked. Place the pillow edge just under the head, bringing the head off the bed with space below for the needle approach.
The brachial plexus can be found in two ways.
1) Identify the subclavian artery and the brachial plexus surrounding it antero-laterally as described here. Traceback the plexus up the neck until the trunks are clearly visible, aim to block at the C5/6 level.
2) Identify the trachea at the level of C6 (thyroid cartilage) and scan laterally, identifying the sternocleidomastoid muscle superiorly, and following it to it's lateral border. The brachial plexus will be identifiable as a number (2-5) of hypoechoic circular structures between the larger hyperechoic scalene muscles (figure 1).
You may need to angle the probe slightly caudally in order to gain the best view of the plexus.
Other structures visible are the phrenic nerve on the superior surface of the anterior scalene (moves medially as you scan up the neck), arterial tributaries traversing the plexus are reasonably common (usually the transverse cervical artery or dorsal scapular artery) and colour doppler should be used to identify these (be aware that use of doppler parallel to an artery will not show flow, an angle needs to be present), the vertebral artery will be present deep to C6 transverse process and above.
Conduct of the Block
We recommend you prepare a block tray with the following; a short bevel block needle (with or without nerve stimulation), syringes, drawing up needle, 25g needle for local infiltration, skin preparation, a small sterile drape (preferably with a hole), sterile ultrasound gel, sterile ultrasound probe cover (sheath or tegaderm), 1% lidocaine for infiltration and 10ml of 0.5% Bupivicaine (or similar), sterile gloves.
Apply standard monitoring.
Give the patient appropriate sedation, such that they are comfortable and able to tolerate the procedure.
After a pre scan to determine optimal probe position and normal anatomy, prepare the skin with your antiseptic, place drape and cover ultrasound probe ensuring no air gap. Scan as described above.
Insert the local infiltration adjacent to intended point of injection, and wait sufficient time to achieve cutaneous analgesia.
Flush the block needle completely with local anaesthetic, then insert in plane (parallel to the long axis of the ultrasound transducer, in the centre of the beam), attempt to visualise the needle at the lateral edge of the picture (it should become visible after it has been inserted 1-2cm into the skin, if not, reposition the probe until it becomes visible, do not insert any further). Angle the needle so that the tip pierces the middle scalene muscle at its posterior border. The needle can then be cautiously advanced through the muscle angled so that its final trajectory will be just below the upper trunk of the brachial plexus. The needle will "pop" through the medial surface of middle scalene, be careful not the go too far and penetrate neural tissue.
Aspirate to ensure the needle has not penetrated a vessel, then cautiously inject 1-2ml of local anaesthetic and ensure that spread is visible from your needle tip. If you are unable to see hypoechoic local anaesthetic emerging, then you have not adequately visualised the needle tip and should reposition the transducer. If the spread is visible next to the plexus, then continue to slowly inject the whole 10ml observing for adequate spread around the nerves, and watching carefully for enlargement of the plexus (which could represent intraneural placement of the needle tip). Injection pressures should be low, and the patient should be observed for paraesthesias or pain during injection.
If a catheter is to be placed, we use a 19g Tuohy tip set, using the same approach, although an out of plane approach can be used which can be easier as the catheter will then run parallel to the plexus. Full aseptic precautions are necessary when placing catheters. Remember to hydrodissect using either local anaesthetic or saline to create "room" for the catheter to enter. Fixation can be achieved with a "Lockit" along with Opsite adhesive spray.