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PERIPHERAL VASCULAR ULTRASOUND
fossa. However, duplex scanning provides good results when compared to contrast venography in areas where compression can be applied, but cau- tion should be used when attempting to diagnose DVT on the basis of Doppler flow patterns (Baarslag et al 2002). Upper limb swelling can also be caused by lymphedema, following mastectomy with removal of lymph nodes in the axilla and the effects of radiotherapy.
TECHNIQUE FOR ASSESSING THE BRACHIAL, AXILLARY AND SUBCLAVIAN VEINS
The patient should lie supine so that the subclavian and axillary veins are distended. The scan normally takes 10–15min for each arm. Remember, it can be useful to compare the scan appearance from both sides in cases of suspected unilateral throm- bosis. It should also be noted that the color flow image of the proximal subclavian vein can look rather confusing and ‘cluttered’ because of the proximity of other vessels and the often pulsatile appearance superimposed on the venous flow pat- tern, due to atrial contractions.
1. The arm should be abducted and placed on a comfortable support. It is easier to start the examination distally in the brachial vein, which will be seen lying adjacent to the brachial artery in the upper arm.
2. The brachial vein is imaged in transverse section and should be compressible with relatively light transducer pressure. Color and spectral Doppler recordings should demonstrate flow augmenta- tion with manual compression of the forearm.
3. The axillary vein can be imaged by using a com- bination of transaxillary and infraclavicular trans- ducer positions (see Ch. 10). The vein will be seen lying adjacent to the artery, but color flow imag- ing can aid identification, particularly if B-mode imaging is poor. A combination of compression and color flow imaging may be needed to confirm patency in this region. The cephalic vein may act as a collateral pathway to the sub- clavian vein in the presence of a distal axillary vein thrombosis.
4. The distal end of the subclavian vein is ini- tially imaged from the infraclavicular fossa in
transverse section, where it will be seen lying i n f e r i o r t o t h e s u b c l a v i a n a r t e r y. T h e m i d - subclavian vein is imaged from the supraclavic- ular fossa. A large acoustic shadow will be seen as the subclavian vein runs under the clavicle. Compression of the subclavian vein is extremely difficult, owing to the contour of the neck and the presence of the clavicle, and color flow imag- ing in transverse and longitudinal planes is used to confirm patency. In addition, spectral Doppler should demonstrate spontaneous phasic flow with respiration if there is no outflow obstruc- tion. It is also usual to observe a pulsatile flow pattern superimposed on the phasic flow pattern due to atrial contractions of the heart (see Ch. 5). It should be noted that it is extremely easy to miss a proximal thrombosis in the subclavian vein, owing to poor visualization of this area, especially if it is a partially occluding thrombus. It is pos- sible to image indwelling catheters, such as Hickman lines, in the subclavian vein. Always state any limitations or doubts about the scan in this region, as other imaging tests, such as venography, may be required.
5. Twobreathingmaneuverscanbeusedforassess- ing flow in the subclavian vein. The first is a Valsalva maneuver, in which there should be cessation of flow or flow reversal during Valsalva. This is followed by an enhancement in flow toward the heart during expiration. The second involves multiple sniffing through the nose. During continued sniffing the subclavian vein will be seen to contract. Neither of these maneu- vers can exclude DVT, as there may be non- occluding thrombus present. However, if an abnormal flow pattern or response is recorded, it may indicate a potential abnormality.
6. Occasionally,athrombosismayinvolvetheinter- nal jugular vein in the neck. This can be imaged in cross section.
7. It is usually impossible to image the brachio- cephalic veins, but a thrombosis may be indi- rectly suggested if there is an abnormality in the subclavian and axillary vein flow patterns.
Other upper limb venous disorders
Phlebitis of the superficial veins can occur due to repeated catheter access or intravenous drug