The subclavian vein is the major vein of the arm, shoulder and neck. Its name means ‘under the clavicle’, due to the course it takes when entering the thorax.
We will discuss the detailed anatomy of this vein in order to give a three dimensional understanding. The vein has a great deal of clinical relevance, which will also be addressed in this article.
Course and important relations
The subclavian vein is a paired large vein, one on either side of the body, and runs under the clavicle and anterior to the artery of the same name.
The diameter is approximately to that of the little finger. Each subclavian vein is a direct continuation of the axillary vein, which passes under the pectoralis minor muscle, and is renamed as the subclavian vein once it passed the lateral border of the first rib. At this point, the superficial vein known as the ‘cephalic vein’ has joined the axillary vein.
The vein now ascends to the medial border of anterior scalene muscle. From here it joins with the internal jugular vein to form the brachiocephalic vein. The brachiocephalic veins exist on both sides, however the brachiocephalic trunk (artery) only exists on the right hand side i.e. the subclavian and common carotid arteries arise directly from the arch of the aorta on the left side. The angle of union of internal jugular and subclavian vein is termed the ‘venous angle’ and is present on both sides.
The subclavian vein follows the subclavian artery and is separated from the subclavian artery by the insertion of the anterior scalene. Thus, the subclavian vein lies anterior to the anterior scalene while the subclavian artery lies posterior to the anterior scalene (and anterior to the middle scalene). The Subclavius muscle lies below the clavicle and joint the first rib inferiorly.
The phrenic nerve runs obliquely with the internal jugular vein and anterior to the anterior scalene muscle. Here it runs posterior to the subclavian vein on both sides and anterior to the root of the lung in the thorax.
There are pairs of valves at the end of the subclavian vein.
The subclavian vein receives venous blood from the internal and external jugular veins of the lateral cervical region, as well as the dorsal scapular vein which drains the region of the same name, as well as the anterior jugular vein, which lies on the front of the neck.
Near the junction of the left subclavian vein and the left internal jugular vein, is where the thoracic duct drains.
Within the lympatic system, is lymph, which consists mainly of solutes and water, in addition to chylimocrins which are the bodies transporters of lipids from the intestines.
In a similar fashion, the right thoracic duct drains into the junction between the right subclavian vein and right internal jugular vein.
Central venous access
If a patient has lost a great deal of blood, or is very difficult to cannulate, central venous access is sometimes required through major veins of the neck. Subclavian vein is one of them. The main purposes behind the catheterization are long term venous access with minimal infections and central venous pressure monitoring. This involves piercing the subclavian vein with a large bore cannula like Swan-Ganz catheter in order to administer fluid and medication.
The commonest site of clavicular fracture is the middle third. When the bone fractures, the medial segment is pulled upward by the sternocleidomastoid, and the lateral segment is pulled downward by the pectoral muscles and weight of the upper limb. The medial fractured segment therefore may cause compression of the subclavian vessels in the clavicular region, including the vein, which lies anterior to the scalenus anterior.
Subclavian Vein thrombosis
This complication is associated with indwelling catheters left in situ for long periods. The catheters induce turbulent blood flow and hence promote abnormal clotting.