Ultrasonographic examination to search out the optimal upper arm position for coracoid approach to infraclavicular brachial plexus block--a volunteer study.

Background: Infraclavicular brachial plexus block has been widely used for surgical procedures below the mid humerus owing to its excellent anesthetic quality and ease of practice. However, what is the optimal upper arm position for carrying out the procedure still lacks consensus of opinion. The primary goal of this study was to determine the optimal upper arm position for coracoid infraclavicular block by ultrasonographic examination.

Methods: High-frequency (5-10 MHz) ultrasonographic examination on the vertical line 2 cm medial to the coracoid process was performed in 40 volunteers. We assessed the influence of four different upper arm positions on the topographic anatomy of the infraclavicular region. Ultrasonography-derived distances and morphometric measurements were applied to evaluate the optimal puncture site. The deviation of coracoid puncture site from the ultrasonographically modified ideal puncture site in distance was also recorded.

Results: When the upper arm was abducted 900, the brachial plexus was much closer to the skin (1.67 cm) and farther from the pleura (1.15 cm) as compared with other positions. In this position, the revealation of anterosuperior plexus relative to artery, identification of all three cords and pleura were 53.8%, 64.1% and 87.2%, respectively. We also found that as the upper arm was drawing from abduction to adduction the ideal puncture site tended to shift more inferiorly.

Conclusions: We recommend the most optimal position for carrying out coracoid infraclavicular brachial plexus block is to abduct the upper arm 90 degrees with external rotation of the shoulder. Though ultrasonographic guidance is suggested for infraclaricular brachial plexus block, an optimal position for puncture site determined by anatomical landmark is also acceptable.