Equipment
An 8-12 MHZ or a curved linear frequency 3-7 MHZ probe can be used. [6] The advantage of a curved probe is it offers a wider field of view. Depending on the thickness of the patient’s chest, the provider can use a linear high-frequency probe.
An 80-100 mm 18-22 gauge block needle is used. The longer length may be needed due to the depth of the nerve bundle at this location. A large-bore needle is preferred when the nerves are deep; this allows better visualization of the needle. If any doubt exists regarding the nature of the structures that look like nerves, an insulated stimulating needle can be connected to a nerve stimulator. These needles tend not to be very echogenic. Specific echogenic needles for ultrasound-guided blocks exist, but the differences tend to be minimal. The needle crosses thick pectoralis muscles in the chest; this can be painful, requiring sedation to keep patients comfortable.
A nerve stimulator may be used as an adjunct to ultrasound images or if an ultrasound is not available. A nerve stimulator is set at 1-1.5 mA pulse frequency of 1 Hz and pulse duration of 0.1 msec. Attach the needle to the nerve stimulator and place the grounder on the patient with an EKG pad.
If a good image is available, 20 mL of local anesthetic is all that is needed (see Anesthesia). Increasing the volume increases the chance of phrenic nerve paralysis. Local anesthetic with a 25-gauge or 27-gauge needle may be needed for a skin wheal and to numb the pectoralis muscle before block needle insertion, usually 1-2% lidocaine.
Resuscitation equipment and medication must be available. Basic monitoring should be in place, with 3-5 lead EKG, NIBP, and pulse oximetry. [3]
Sterile prep such as ChloraPrep (preferred) and sterile ultrasound gel are needed. The authors use a sterile Tegaderm to place over the ultrasound probe and place the sterile ultrasound gel over the Tegaderm. [3] A printer can be attached to the ultrasound to get still images for the patient’s record.
Anesthesia
For surgical anesthesia in adults, a single shot of 30 mL of 1.5% mepivacaine plain will provide close to immediate (5 min) to 2-3 hrs of surgical analgesia. For longer surgical anesthesia, up to 3-4 hrs, 1:400,000 epinephrine is added to the solution. The block completely resolves about 2 hrs later. If a longer block is needed, adding tetracaine at 2 mg/mL (0.2%) prolongs the block to 4-6 hrs. Another option for fast onset and long-term analgesia is mixing 15 ml of 1.5% mepivicaine with 15 ml of 0.5% bupivicaine and injecting.
For longer postoperative analgesia, 0.25% ropivacaine or bupivacaine is used and should provide more than 12 hrs of pain relief. The onset will be delayed from 5 min to about 20 min. For both perioperative and postoperative pain control, a combination of both can be used. No more than 40 ml should be injected taking into consideration the patient's weight and the toxicity dose of the local anesthetic used.
Positioning
Patient is in a semi-sitting position with arm to be blocked down and at 45°.
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Formation of brachial plexus rami, trunks, divisions, cords, roots and nerves.
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Innervation of the arms and hands.
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The cephalad-to-caudad approach.
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Ultrasound image of the needle in plane with local anesthetic posterior to the axillary artery. Arrows = block needle, AA = axillary artery, LA = local anesthetic posterior to the artery.
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Ultrasound orientation of the muscles, arteries, and nerves in a transverse view. Short axis (transverse view)-AA=axillary artery, Arrowheads=cords, AV=axillary vein, PMM=pectoralis major, PMIM=pectoralis minor 9-12 o‘clock is cephalad to artery=lateral cord, 6-9 o'clock is posterior=posterior cord, 3-6 o'clock is caudad is medial cord. Medial cord is often hard to visualize.
