Pinprick anesthesia to a 23-gauge needle and motor block were checked by an independent observer every 5 min for 30 min in the median, ulnar, radial, and musculocutaneous nerve locations. A successful block was defined as complete sensory and motor block in all regions assessed within 30 min of local anesthetic injection. Anesthetic failure in the surgical area was supplemented with local anesthetic infiltration or general anesthesia if necessary.
Also monitored were the time required for block performance (the time elapsed from probe positioning to the end of local anesthetic injection), the number of needle attempts, the pattern of local anesthetic spread, postblock complications, visual analog pain scores in the postanesthesia care unit (PACU), and patient satisfaction. Continuous data are expressed as mean ± sd.
Forty patients (26 men and 14 women, 45 ± 15 yr old, 170 ± 11 cm, 77 ± 15 kg, with a body mass index of 26 ± 5 kg/m2) completed the study. Surgical time was 77.9 ± 40.4 min for 2 forearm, 9 wrist, and 29 hand and finger procedures. Ultrasound showed in all cases the transverse view of the brachial plexus as hypoechoic nodules in clusters of varying size, consistently lateral, posterior, and often cephalad to the subclavian artery.
Blocks performed by 5 anesthesiologists (1 staff, 1 fellow, and 3 residents) were successful in 95% (38 of 40) of the cases. The block procedure took 9.0 ± 4.4 min after 1 attempt (median; range, 1–2), even though only 2 investigators had prior ultrasound experience (≤5 cases). Contraction was elicited by a stimulating current of 0.46 mA (range, 0.2–0.7 mA) in one or more muscle groups, corresponding to stimulation of the radial, median, musculocutaneous, and ulnar nerves in 55%, 30%, 10%, and 8%, respectively. Sensory and motor block appeared within 5.4 ± 1.8 min, was completed within 16.7 ± 5.5 min, and resolved in 11.4 ± 4.2 h. Postoperative PACU pain scores were low (mean, <0.3 of 10), and patient satisfaction with pain control was high (median, 9 out of 10).
One failure was attributed to subcutaneous injection that we failed to recognize despite an unusual spread pattern observed on ultrasound at the time of injection. The second failure, an incomplete block at 30 min, was attributable to partial intravascular local anesthetic injection but was subsequently found to be complete at the end of surgery. Postoperative complications included one case of Horner’s syndrome and one transient paresthesia (<48 h), but no pneumothorax.
Our preliminary results suggest that ultrasound guidance for supraclavicular brachial plexus block is clinically useful for accurate nerve localization and to minimize the number of needle attempts. Nerve localization was confirmed by two methods in this study: ultrasound and electrical stimulation. Whether ultrasound alone can offer the same success deserves further study. Unlike estimates by conventional techniques, ultrasound can determine the size, depth, and exact location of the brachial plexus and its neighboring structures. Preblock anatomical examination can define the optimal site and depth of needle insertion, avoid vascular and pleural puncture, and impart confidence to anesthesiologists performing the block.
Real-time ultrasound imaging can help guide the block needle to reach target nerves with fewer attempts. Under visual guidance, needle movement is purposeful and based on constant image feedback, thus avoiding nerve localization by trial and error. Our technique of needle insertion is unique and drastically different from those conventionally taught. With one hand holding the probe, the other advances the block needle from the outer end of the probe in a lateral to medial direction (Fig. 2), for two main reasons. First, when positioned in the supraclavicular fossa, the probe leaves limited space on the medial side for needle maneuvering. Second, the brachial plexus is situated lateral to the subclavian artery; thus, the lateral approach is most logical and direct. Although Kapral et al. (5) and Yang et al. (6) both reported block success with ultrasound guidance, the technique of needle placement was not disclosed. Furthermore, the brachial plexus was scanned in the sagittal (longitudinal) plane as opposed to the coronal oblique (transverse) plane in this study.
Real-time observation of needle movement is an important feature of the ultrasound technique we describe. The needle is advanced intentionally in the same plane as the ultrasound beam, i.e., along the along axis of the probe, where the linear array of ultrasound crystals is situated. With proper needle-probe alignment, movement of the needle shaft and tip (a hyperechoic line seen in Fig. 3) can be tracked continuously during the block procedure. When the needle does not trespass the first rib or pleura on ultrasound, the risk of pneumothorax is virtually eliminated. However, without proper alignment, the needle tip cannot be fully visualized, and penetration can be deeper than anticipated, as with the case of unrecognized subclavian artery puncture in this study.
Ultrasound imaging shows nerves as mobile structures that move away from the needle or local anesthetic injection. Two patterns of local anesthetic spread have been observed. In the first pattern, bolus injection within the nerve cluster pushes the nerves to the periphery, suggesting circumferential spread (Fig. 4). Expansion of the nerve-containing compartment is lined by a hyperechoic perimeter, possibly representative of the plexus sheath. In the second, spread is asymmetrical, with local anesthetic in contact with only some part of the nerve cluster without the apparent sheath (Fig. 5). When this happens, we intentionally make a second injection, but it is unclear whether double injection is necessary to guarantee complete anesthesia.
In summary, we found that ultrasound guidance is clinically useful for supraclavicular brachial plexus block. It confers confidence and accuracy of needle placement for nerve localization and examines the pattern of local anesthetic spread.
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© 2003 International Anesthesia Research Society
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