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PART 4 — PERIPHERAL VENOUS
However, venous duplex imaging is extremely ex- aminer-dependent. Studies done improperly will be inaccurate. A patient who has been misdiagnosed with a venous thrombosis may be subjected to lengthy an- ticoagulant therapy with the risks and expenses that go with it. Conversely, a patient with an undiagnosed venous thrombosis due to an improperly performed ultrasound examination may have a life-threatening problem go undetected. This is a common tale due to the lack of standardization of qualifications for those performing venous ultrasound examinations.
The solution to this problem is to have those per- forming venous exams follow proper protocols and to have adequate supervised experience. The protocol in this chapter will ensure the best likelihood of perform- ing the venous duplex ultrasound examination, using techniques that will produce accurate results.
When performing venous duplex ultrasound im- aging, the examiner is trying to assess three things:
1. The presence or absence of thrombus
2. The relative risk of the thrombus dislodging
and traveling to the lungs
3. The competence of the contained valves
Venous duplex ultrasound is a great tool for deter- mining each of the items previously listed. The so- nographer performing venous examinations must understand the venous anatomy.5–8 Additionally, it is helpful to understand the pathophysiology, risk factors, and symptoms associated with DVT. This chapter will provide a comprehensive review of information pertaining to the venous duplex ultra- sound examination and DVT.
ANATOMY
Chapter 1 of this text provided an anatomy review and diagrams of the vascular system. Continuing this discussion, a vascular technologist or sonographer needs to clearly understand the three main catego- ries of veins that can be imaged:
1. The deep veins
2. The superficial veins 3. Perforators
DEEP VEINS
The deep veins are the freeways of the venous sys- tem. They are the main conduit for blood returning to the heart and are surrounded by muscle. They ac- company an artery of the same name. A thrombus within the deep veins is likely to be dislodged because the muscle squeezes the deep veins with each step taken. This squeezing action is the main force that propels blood out of the leg and back to the heart, but it can also be the mechanism for dislodging a con- tained thrombus into the venous system, producing
a pulmonary embolism (PE). A thrombus found in a deep vein is usually larger than a thrombus found in a superficial vein. This makes the thrombus from a deep vein more likely to cause a life-threatening PE because the thrombus has the potential to become lodged in a larger caliper pulmonary artery branch.
SUPERFICIAL VEINS
Unlike the deep veins, the superficial veins travel close to the skin, superficial to the muscle. These veins are usually smaller than their deeper counterparts and travel without an accompanying artery. They have an entirely different function than the deep veins. Their purpose is to get blood near the skin so as to help reg- ulate body temperature. If the body needs to get rid of heat, the superficial veins engorge and heat from the blood-filled veins escapes into the air. If the body needs to conserve heat, the superficial veins contract and shunt blood away from the skin so the heat from the contained blood is not lost.
The traditional wisdom is that thrombi in the su- perficial veins do not embolize so there is often less concern about a thrombus in the superficial system. This is not true. Thrombi from the superficial venous system do embolize and travel to the lungs. However, thrombi are generally less likely to embolize from the superficial veins because they are not surrounded by muscle similar to the deep veins. Thrombi in the su- perficial veins are usually smaller in caliber than a thrombus in the deep veins, but their size can vary. If a thrombus is located in a superficial vein near the junction with a deep vein (the saphenofemoral or sa- phenopopliteal junctions), it has a greater potential to propagate into the deep veins. A thrombus in the superficial veins must be evaluated carefully to judge its potential risk to the patient.
PERFORATORS
Perforators are small bridges that connect the deep veins with the superficial veins. Their role is to keep blood from spending too much time near the skin surface by moving blood from the superficial veins to the deep veins. They have one-way valves that en- sure blood is moving in the proper direction. When these valves do not function, blood can pool as the patient sits or stands too long. Over time, this can lead to chronic stasis changes and the possibility of venous ulcerations.
EPIDEMIOLOGY
Venous thromboembolism (VTE) consists of ve- nous thrombosis (superficial or deep) and/or PE. PE is primarily a complication of DVT and a leading