Probe placement for supraclavicular block is near the sagittal plane by visualizing the subclavian artery (SA) immediately posterior to the clavicle and holding the probe between the base of the neck and the clavicle (Fig. 21.3). The probe is angled slightly medially but mainly cau-dad, and the probe is rotated on its axis with its anterior edge more medial than its posterior to produce the best short-axis view of the pulsatile SA (Fig. 21.6a). A bright, hyperechoic line is seen deep to the artery which is reflected ultrasound from the first rib and the pleura of the lung deep to the rib. A cluster of hypoechoic round structures resembling a "grape cluster" is identified lateral, posterior, and superior to the artery and often extends down to the rib or may be more horizontal in orientation. It is uncommon to see three distinct trunks, but rather to see fascicles within those trunks or divisions at this level. Posterior to the fascicles, the middle scalene muscle can be identified and the anterior scalene muscle found anterior and medial to the SA. Superficial to the supraclavicular brachial plexus will be the omohyoid muscle and often the pulsatile superficial cervical or suprascapular arteries that arise from the thyrocervical trunk. Occasionally, the clavicular anatomy limits optimal movement of the linear ultrasound probe, and a probe with a smaller head/footprint may be necessary for better visualization of the artery, nerves, and rib or pleura prior to needle placement.
The ultrasound supraclavicular technique is an efficient and very effective block of the brachial plexus that blocks all trunks/divisions quickly and typically with a lower volume of local anesthetic than required for most other brachial plexus approaches (Winnie and Collins 1964). The confined nature of the brachial plexus at this point between the first rib
and the clavicle allows for easier localization/spread and restriction of local anesthetic flow to intended targets.
With approaches other than USGRA of the brachial plexus in the supraclavicular area, there is a somewhat higher risk of pneumothorax (approx. 0.5-3%) that can often be delayed in presentation (Franco and Vieira 2000). A pneumothorax is a major deterrent to practitioners who may wish to send patients home following an ambulatory surgical procedure in which a supraclavicular block was placed. In addition, with a technique other than USGRA together with the pulsatile nature of the SA, the ulnar nerve distribution of the brachial plexus is often spared an effective block secondary to poor diffusion of the local anesthetic posterior and caudally within the neurovascular bundle. The use of ultrasound appears ideal in this circumstance, because the first rib, pleura, and SA are readily visible and can be easily avoided provided the practitioner maintains vigilance in keeping the block needle tip in vision under ultrasound during the entire procedure of PNB placement (Fig. 21.6b).
USGRA of a supraclavicular block usually has the PNB needle inserted in-plane with the ultrasound probe so that the needle tip is constantly visualized and inadvertent puncture of the pleura is minimized (Fig. 21.6b). Usually a high-frequency (>10 MHz) linear array probe is used for most brachial plexus approaches (with the possible exception of an infraclavicular nerve block) to allow increased resolution of the superficial brachial plexus structures. The needle is typically inserted at a point lateral to the probe and directed toward inferior and medial portion of the plexus between the first rib and the artery. Needle movement and local anesthetic spread should be directed to the middle and lower trunks/divisions of the plexus by placing the needle tip close to the first rib prior to local anesthetic injection. Typically, an USRA supraclavicular technique requires 20-30 ml of local anesthetic to produce a successful block. Smaller volumes may provide successful anesthesia, and this is currently being studied.
An indwelling PNB catheter technique is possible using the described method with a Tuohy needle, but catheter fixation may be somewhat more difficult than that of an infraclavicular technique (described below). A common side effect of this PNB technique is the occurrence of Horner's syndrome secondary to the proximity of the sympathetic chain at
Figure 21.6b Supraclavicular ultrasound anatomy. Image demonstrates anatomy of the supraclavicular brachial plexus with needle approaching the brachial plexus in-line with the ultrasound probe. Note the local anesthetic spread around the nerve plexus.
this level. In addition, phrenic nerve blockade may be as frequent as 60%. Other potential complications include pneumothorax (previously mentioned), infection, hematoma, local anesthetic toxicity, patient discomfort, neurologic injury, and failed block.
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