Ultrasound imaging of the axillary vein - anatomical basis for central venous access

Background. The central veins that are usually cannulated are the jugular, subclavian, femoral and brachial. If subclavian catheterization is difficult using surface landmark techniques, we now use ultrasound to catheterize the infraclavicular axillary vein. This approach is not widely used and the ultrasound appearance has not been formally described. We examined the anatomical relationships of the axillary vessels to guide safe cannulation of the axillary vein. Method. In 50 subjects, we used ultrasound to examine the infraclavicular regions from below the mid-clavicular point and at 2 cm and 4 cm further laterally (described as the middle and lateral points) with the arms at 0degrees, 45degrees and at 90degrees abduction. We took measurements at each point, with the artery and vein seen in cross-section. The depth from the skin, vessel diameters and the distance between the vessels was measured. The amount of overlap was scaled from 0 (no overlap) to 3 (complete overlap). We also recorded (if visible) the distance between the rib cage and axillary vein. A longitudinal image of the vein was also obtained. Angle of ascent (in relation to the skin), length and depth of the vein was measured. Results. Axillary vessels were seen in 93% of images. The mean depth from skin to vein increased from 1.9 cm (range 0.7-3.7 cm) medially to 3.1 cm (1.1-5.6 cm) laterally. The venous diameter decreased from 1.2 cm (0.3-2.1 cm) medially to 0.9 cm (0.4-1.6 cm) laterally. The arterio-venous distance increased from 0.3 cm to 0.8 cm. Median arterio-venous overlap decreased from 2/3 (mode 3/3) to 0 (0). The distance from rib cage to vein increased from 1.0 cm to 2.0 cm. Conclusion. The axillary vein is an alternative for central venous cannulation and we present an anatomical rationale for its safe use. Less arterio-venous overlap and a greater distance between artery and vein and from vein to rib cage should provide an increased margin of safety for central venous cannulation.