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°, 15°, 30°, 45° and 60° from the midline was associated with increasingmedial deviation. The brachial plexus becamemore superficial if head rotation was over 30° than within the realm of 15°. The likelihood of the stimulated needle path intersecting the internal jugular vein was lower than 5% for head rotation within 30° and would become significantly higher for head rotation over 45°. Conclusions: Whenever we perform interscalene brachial plexus block, the head rotation angle should not exceed 30°. The measured medial deviation of surface landmark should be considered when it is used to approach interscalene brachial plexus.