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PERIPHERAL VASCULAR ULTRASOUND
transducer should be used to image the veins. Starting at the top of the leg, the long saphenous vein should be identified in transverse section at the level of the saphenofemoral junction and fol- lowed distally down the thigh and into the calf. Scanning the vein in transverse section is important, because it is easier to assess its diameter and to identify any large branches dividing from the vein, or duplicated or bifid systems. The diameter of the vein should be recorded at frequent intervals throughout its length. Ideally, the diameter should be greater than 3mm to be suitable as a graft. Veins of less than 2 mm in diameter are regarded as too small to be used for femoral distal bypass grafting. Veins that become excessively large (0.8 cm diameter) or grossly varicose may also be unsuit- able, and this should be drawn to the attention of the surgeon. The common femoral vein, superficial femoral vein and popliteal vein should always be examined when vein mapping to ensure deep venous patency, as the long saphenous vein can act as an important collateral pathway if the deep veins have been obstructed and, in such circumstances, should not be harvested for a graft. In this situa- tion, other sources of vein can be assessed.
Arm vein mapping
It is not uncommon to find that part or all of the long saphenous vein is unsuitable for use as a graft because it is too small, because it is varicose or because the deep veins are obstructed. In addition, the long saphenous vein may have already been removed for coronary artery bypass surgery. The cephalic or basilic veins of the arm can be harvested for bypass grafts provided they are of adequate diameter. The cephalic vein is the vein of choice, as it is longer than the basilic vein, and the anatomy of the basilic vein is more variable in its proximal segment. To image the veins, the arm should be in a comfortable dependent position with the palm facing upward. The cephalic vein can be located in transverse section along the outer aspect of the forearm 2–3 cm above the wrist, lateral to the radial artery and followed proximally. Alternatively, it can be located in the anterior aspect of the upper arm, lying superficial to the biceps muscle and then fol- lowed proximally toward the shoulder and then distally into the forearm. The vein can be difficult
C
AH
B
(B), cephalic vein (C) and brachial artery and veins (A). The arm was positioned with the palm up so that the cephalic vein lies on the anterior aspect of the arm and the basilic vein and brachial vessels on the medial aspect. The humerus is also seen (H).
A transverse B-mode montage of the left upper arm demonstrating the position of the basilic vein
Figure 14.23
to follow as it crosses the antecubital fossa, as there are a number of superficial veins crossing this area. The basilic vein is easiest to locate with the arm extended outward (abducted) and the palm facing upward. The probe is placed on the medial aspect of the arm 2–3 cm above the elbow joint. Imaging in cross-section, the basilic vein should be seen as sep- arate from the brachial artery (Fig. 14.23). The vein can then be followed proximally, where it is usually seen to course toward the proximal brachial vein or the axillary vein, although there can be anatomical variation of the veins in this region. Following the basilic vein distally into the forearm can be confus- ing, as it sometimes joins the cephalic vein in the forearm via the median cubital vein, but it usually runs toward the medial (ulnar) aspect of the wrist. One potential pitfall of mapping the basilic vein is accidentally confusing it with the brachial artery, but use of probe compression to collapse the vein and color flow imaging should avoid this error.
Technique of marking the vein
There are two techniques for marking leg or arm veins (Fig. 14.24). Using the first method, the vein