Ultrasound anatomy of the infraclavicular region. Visibility and features of the brachial plexus and its relationship with the surrounding vascular structures.

Introduction: to check visibility, number, position of the nervous cords forming the brachial plexus in the infraclavicular region; evaluate the relationships with subclavian artery and subclavian vein. Methods: a Mylab 30 Gold (Esaote) Ultrasound machine with a High frequency linear probe (LA 523 7.5 MHz) was employed. The aim of the probe orientation was to acquire an image of the infraclavicular structure by a lateral approach (1). The probe was oriented sagittally and parallel to the anterior wall of the shoulder girdle, beneath the clavicula, and perpendicular to the suspected path of the axillary vessels. The patient was made to lie supine, with arms placed in a neutral position, along the body. The probe was minimally moved, with slight adjustments, in order to obtain a transverse sonogram showing the subclavian artery, seen as a round-pulsating echo-lucent circle; it was firmly maintained centrally (fig. 1). The image was frozen. Two expert anesthesiologists evaluated the appropriate adjustment, depth and focus of the target, number, location and relationships between the plexus cords and the subclavian vein. Data are presented as percentages, mean ± SD or median (range). Fig 2:Anatomic structures of the infraclavicular region and percentage of visualization. Results: 202 patients scheduled to undergo elective major surgery of the upper limb were selected to receive the brachial plexus block by an infraclavicular approach. The number of detected cords was 3 in 72 patients, 2 in 76 and 1 in 51. Posterior cord was visualized in 55% of the patients, lateral cord in 80% and medial cord in 69%. The average orientation of the identified cords respect to the artery was 77° for medial cord, 316° for lateral cord and 179° for posterior cord. The position variability resulted smaller for posterior cord (±18°) and larger for medial and lateral ones (respectively ±57°, ±28°). The subclavian vein was found to be not visible in 20 patients (10%), was 1 in 125 patients (62%), the visible veins were 2 in 33 patients (16%) and more than 2 in 3 patients (1%). It turned out to be larger than the artery in 107 patients and smaller in 45 patients; the average position in respect to artery was of 142° with a high variability: ± 88°, median 120° (range 0-360°). Discussion: the ultrasound- guided anatomic evaluation of the infraclavicular region could furnish important items in order to obtain a higher success rate and fewer complications performing brachial plexus block.