Ultrasound examination for the optimal head position for interscalene brachial plexus block.

Background: Surface anatomic landmarks have traditionally been used to locate the brachial plexus in the interscalene groove. Head rotation can affect the orientation of neck vessels and may possibly affect the brachial plexus. The optimal degree of head rotation has been specified for better internal jugular vein cannulation but not for interscalene brachial plexus block. The purpose of this study was to evaluate the influence of head rotation on interscalene brachial plexus block.

Methods: We simulated the needle insertion in interscalene approach to brachial plexus with the ultrasound probe to mimic the needle in the manner of actual block in 53 volunteers. Ultrasound-derived measurements were recorded to evaluate the influence of head rotation on the approach including deviation from the imitative needle path to plexus center, depth of brachial plexus and vessel intersection.

Results: Medial deviation of the imitative needle path to the center of brachial plexus was found from all angles of head rotation. Increased head rotation angle of 0 degree, 15 degrees, 30 degrees, 45 degrees and 60 degrees from the midline was associated with increasing medial deviation. The brachial plexus became more superficial if head rotation was over 30 degrees than within the realm of 15 degrees. The likelihood of the stimulated needle path intersecting the internal jugular vein was lower than 5% for head rotation within 30 degrees and would become significantly higher for head rotation over 45 degrees.

Conclusions: Whenever we perform interscalene brachial plexus block, the head rotation angle should not exceed 30 degrees. The measured medial deviation of surface landmark should be considered when it is used to approach interscalene brachial plexus.