The subclavian vein is the continuation of the axillary vein and runs from the outer border of the first rib to the medial border of scalenus anterior where it joins with the internal jugular vein to form the innominate vein (Figure 1). The vein is separated posteriorly from the subclavian artery by the insertion of scalenus anterior and postero-medially from the dome of the pleura by Sibson's fascia (suprapleural membrane). These relationships are illustrated in Figure 2.

Anteriorly, the medial third of the clavicle overlies much of the subclavian vein. Because the clavicle is used as a landmark for locating the vein, an understanding of the relationship between these two structures is crucial for successful venepuncture. In particular, the effect of changes in shoulder position must be understood. If the shoulder is elevated, the acromial end of the clavicle moves cephalad, the vein assumes a more inferior and medial relationship to it and the subclavicular portion of the vein is effectively shortened ¹. It is for this reason that subclavian venepuncture should be performed with the shoulder in the neutral position and in slight retraction. The effects of variation in shoulder position on the relationship between the clavicle and the subclavian vein have recently been elegantly analysed by Tan et al ².

The first rib slopes downwards at an angle of about 45 degrees (Figure 3). The pleura tracks the inner border of the rib, and, as a result, the highest point of the pleural cavity is about 3 cms above the point where the subclavian vein crosses the medial border of the rib. Thus, the risk of inadvertent pleural puncture increases the more the searching needle is allowed to stray posteriorly (Figure 4).

The external jugular vein joins the subclavian vein as it crosses the first rib. The passage of a wire or catheter from the EJV into the subclavian vein can be difficult because entry of the EJV is more or less at right angles to the subclavian vein and a valve is also frequently present at this point.

The phrenic nerve courses downwards on the surface of scalenus anterior to enter the thorax by passing between the subclavian artery and vein. In 45% of cases an accessory branch of this nerve passes anteriorly to the vein ³ and thus may be at risk of damage during attempted venepuncture. However, the risk appears to be largely theoretical, as phrenic nerve paralysis has never been reported as a complication of subclavian cannulation. In the setting of cardiac surgery, phrenic nerve damage is far more likely to be caused by either a cold-induced injury resulting from the myocardial protection technique or possibly mechanical injury complicating internal mammary artery harvesting ⁴.

On the left side, the thoracic duct enters the subclavian vein near its junction with the internal jugular vein (Figure 5). The duct constitutes the entire lymphatic drainage of the body except for that of the right arm, and the right half of the head, neck and thorax. Most importantly, the cisterna chyli, which collects the lymphatic drainage of the gut, drains into the thoracic duct. Consequently, trauma to the duct can lead to a persistent chylothorax ⁵.

The venous anatomy of the thoracic inlet is summarised in Figure 6.

1. Land RE. The relationship of the left subclavian vein to the clavicle: practical considerations pertinent to the percutaneous catheterization of the subclavian vein. J Thorac Cardiovasc Surg. 1972 Apr;63(4):564-8

2. Tan BK, Hong SW, Huang MH, Lee ST Anatomic basis of safe percutaneous subclavian venous catheterization. J Trauma 2000 Jan;48(1):82-6.

3. Talbot RW Anatomical pitfall of subclavian venepuncture. Ann R Coll Surg Engl 1978 Jul;60(4):317-9

4. Tripp HF, Bolton JW Phrenic nerve injury following cardiac surgery: a review. J Card Surg 1998 May;13(3):218-23

5. Ruggiero RP; Caruso G Chylothorax--a complication of subclavian vein catheterization. J Parenter Enteral Nutr, 9:750-3, 1985

Last edited on: 26/12/2000