Anesthesia Management |
|Part C:||Anesthesia Techniques|
|Chapter 43:||Nerve Blocks|
The supraclavicular approach to the brachial plexus is anesthetically efficient; a small volume of solution can be delivered at a point in which the three trunks are compactly arranged, resulting in rapid onset of reliable blockade of the brachial plexus. The block can also be performed with the patients arm in any position, to provide excellent anesthesia for elbow, forearm, and hand surgery.
Reliable supraclavicular blockade requires elicitation of a paresthesia. The classic block may be somewhat difficult to describe and to teach. Observation of an experienced anesthesiologist is perhaps the best way to learn the technique. A proposed modification of the technique, the so-called plumb-bob approach, may decrease complications and may simplify the concept of this block. 12
The prevalence of pneumothorax following supraclavicular block ranges from 0.5 to 6 percent and diminishes with experience. The onset of symptoms is usually delayed and may take up to 24 hours. Routine chest radiography after the block is, therefore, not justified. The supraclavicular approach is best avoided when the patient is uncooperative or cannot tolerate any degree of respiratory compromise because of underlying disease. Other complications include frequent phrenic nerve block (4060%), Horner syndrome, and neuropathy. The presence of phrenic or cervical sympathetic nerve block usually requires only reassurance. Although nerve damage can occur, it is uncommon and usually is self-limited.
Several anatomic points are important in the performance of the supraclavicular approach. The three trunks are clustered vertically over the first rib cephaloposterior to the subclavian artery, which can often be palpated in a slender, relaxed patient. The neurovascular bundle lies inferior to the clavicle at about its midpoint. The first rib acts as a medial barrier to the needles reaching the pleural dome and is short, broad, and flat with an anteroposterior orientation at the site of the plexus.
The patient is placed in a supine position, with the head turned away from the side to be blocked. The arm to be anesthetized should be adducted and the hand should be extended along the side toward the ipsilateral knee as far as possible. In the classic technique, the midpoint of the clavicle should be identified and marked. The posterior border of the sternocleidomastoid can be easily palpated when the patient raises the head slightly. The palpating fingers can then roll over the belly of the anterior scalene muscle into the interscalene groove, where a mark should be made approximately 1.5 to 2.0 cm posterior to the midpoint of the clavicle. Palpation of the subclavian artery at this site confirms the landmark.
After appropriate preparation and injection of a skin wheal, the anesthesiologist stands at the side of the patient facing the patients head. A 22-gauge, 4-cm short-bevel needle is directed in a caudad, slightly medial and posterior direction until either a paresthesia is elicited or the first rib is encountered. If a syringe is attached, this orientation causes the needle shaft and syringe to lie almost parallel to a line joining the skin entry and the patients ear. If the first rib is encountered without elicitation of a paresthesia, the needle can be systematically walked anteriorly and posteriorly along the rib until the plexus or the subclavian artery is located (Fig. 434 and Plate 3). Location of the artery provides a useful landmark; the needle can be withdrawn and reinserted in a more posterolateral direction that will usually result in a paresthesia. When a paresthesia has been obtained, aspiration for blood should be performed prior to incremental injections of a total volume of 20 to 30 mL of solution. A nerve stimulator can also be used to identify the brachial plexus.
|FIGURE 434 (A) Supraclavicular block. The needle is systematically walked anteriorly and posteriorly along the rib until the plexus is located. (B) The three trunks are compactly arranged at the level of the first rib.|
|Plate 3. Supraclavicular block. The three trunks are compactly arranged at the level of the first rib. The needle is systematically walked anteriorly and posteriorly along the rib until the plexus is located.|
Usually, the rib is contacted at a needle depth of 3 to 4 cm; however, in an obese patient or in the presence of tissue distortion resulting from hematoma or injection of solution, the depth may exceed the needle length. Nonetheless, gentle probing in the anterior and posterior directions should be done at the 2- to 3-cm depth if paresthesias are not obtained before the needle is advanced farther. Multiple injections may improve the quality or may shorten the onset of blockade.
The modified, plumb-bob approach uses similar patient positioning, although the needle entry site is at the point at which the lateral border of the sternocleidomastoid muscle inserts into the clavicle. After preparation and injection of a skin wheal, a 22-gauge, 4-cm short-bevel needle is inserted while mimicking a plumb bob suspended over the needle entry site. Often, a paresthesia is elicited prior to contacting the first rib or artery. If no paresthesia is elicited, the needle is reinserted while angling the tip of the needle cephalad. If still no paresthesias are obtained, the needle tip is angled caudad in small steps until the first rib is contacted (Fig. 435).
|FIGURE 435 Supraclavicular block. Plumb-bob approach.|
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