What is Venous Ultrasound
Ultrasound waves are high frequency sound waves that can render a visible image of solid structures due to their differences in tissue density and can determine blood flow using Doppler technology that reflects waves back from things in motion, such as red blood cells. This makes it ideal for non-invasive investigation into blood vessels, both arterial and venous.
Veins and Arteries–Similarities and Differences
The arterial system is a high-pressure flow of oxygenated blood to tissues throughout the body; the venous system is a low pressure return of the deoxygenated blood back to the heart. Their similarity in carrying blood sees them sharing similar conditions, but their the differences also provide them opportunities to develop abnormalities unique to each.
Veins have thin walls compared to arteries. The low pressure within veins aids in the blood return to the heart, especially with the aid of the legs acting as a compression/decompression pump during movement and ambulation. This low pressure can also fall victim to obstruction more easily than in their arterial counterparts. Failed valves (venous insufficiency) that would normally keep blood from flowing back in reverse interfere with venous function, and blood can pool as venous stasis.
Venous stasis interferes with the physiologic dynamic of gas exchange at the tissues. When the venous circulation is stalled, there is resistance to flow at the more minuscule depths of tissue and the oxygen-carbon dioxide exchange is compromised. This interference with oxygenation and nutrition can cause tissues to become ischemic, break down, become infected, and undergo gangrenous necrosis (die). In this way venous stasis contributes to ulcerations commonly seen in immobilized persons, especially at pressure points where tissue trapped between bony points and hard surfaces halt blood flow altogether.
Veins that cannot overcome the increased pressure from obstructed flow will swell as varicose veins, ranging from the small spider veins (telangiectasias) to large varicosities which can become infected or burst, which is much more serious than the mere cosmetic concerns a patient may fear.
Blood can also clot, which can cause obstruction to flow as well as pose the hazard of clot separation and migration toward the heart where they can be propelled into the lung circulation as pulmonary emboli.
Ultrasound allows a non-invasive way to investigate these medical conditions. It also allows venous access for intravenous medication and fluids when veins are difficult to find, as well as aids in placing central lines into the larger veins of the body. Almost 8% of hospitalized patients need such central access to jugular, subclavian, and femoral veins and ultrasound is important in locating access points, visualizing the progress of placement in real time, and for their maintenance.
Venous Ultrasound Diagnosis
A venous ultrasound test is painless, simple, and readily available. A transducer (ultrasound broadcaster and receiver) is placed on the area under surveillance and the reflected waves are computed digitally to construct an image.
The venous ultrasound tests are important in that they offer the following advantages:
- Easier and less traumatic central line placement into the internal jugular vein or femoral vein when compared with the use of landmarks alone. Many professional organizations, including cardiovascular anesthesiologists, now recommend it as the initial step in placing central lines.
- Placement of peripherally inserted central catheters (PICCs), another way to gain central access, but through the easier-to-place veins of the upper extremity, e.g., brachial and basilic veins. This type of a line eliminates much of the frequent discomfort that comes from drawing frequent blood samples from patients who are being followed closely via serial blood tests.
- Maintenance of central lines to identify and remedy any line migration or improper positioning.
- Peripheral IV placement in patients who are obese or scarred from previous IV therapy, chemotherapy, IV drug abuse, previous surgery, or radiation. Also, as surgical patients require IVs and with most of them asked to fast from the night before, dehydration will collapse normally visible veins and render them impossible to identify.
- Map out veins for donation in autologous bypass grafting, such as in coronary artery bypass grafting.
- Confirm correct intraosseous (marrow) needle placement.
Diagnosis of the following are made possible by non-invasive ultrasound testing:
- Diagnosis of lower extremity conditions such as venous stasis and life-threatening conditions such as thrombophlebitis, deep vein thrombosis, or pulmonary emboli
- Identify tumors of vascular origin
- Identify congenital malformations, such as arteriovenous fistulas
- Post-traumatic appraisal of circulation in a traumatized limb
- Identify clues to infection, such as a greater-than-normal blood flow
Management of Disease Found by an Ultrasound
Duplex ultrasonography (combined B-mode and Doppler) has replaced catheter-based contrast venography. When chronic venous disease is diagnosed, its management and treatment can be followed via ultrasound as interval evaluations for efficacy of treatment.
Advanced Venous Disease
Advanced venous disease includes edema, skin changes, and ulcerations. If initial conservative medical management fails (compression, elevation, ulcer care), more aggressive treatments can be implemented, such as endovenous interventions:
- Ablating (destroying) venous areas of insufficiency (reflux)
- Removing veins or ablation. Such interventions reduce the amount of blood in the venous circulation of a limb, thereby lessening the venous hypertension in the tissues
- Surgical control of bleeding varicose veins, followed by ultrasound to identify any remaining venous reflux
- Management of recurrent vein thrombosis
- Venous stenting or reconstruction, to recanalize previously obstructed veins
The destruction of veins can be done in two ways:
- Surgical excision: This is the mechanical removal of problematic veins.
- Sclerotherapy: Ablation is via chemical or thermal destruction.
Medical Management of Thrombotic Disease
Anticoagulation is the preferred treatment for deep vein thrombosis (DVT), as soon as possible, since the longer the clot remains, the more likely it will break off and migrate as an embolus. The duration of treatment is individualized, but is usually prolonged, at least three months.
Follow-up is via serial ultrasound surveillance for clot resolution and to rule out clot extension.
Other Treatment Using Ultrasound
- Tendinopathy: Ultrasound can generate a deep heat in inflamed tissues, which stimulates blood flow that hastens healing and delivers anti-inflammatory cytokines to the inflamed areas. Ultrasound is used to deliver this therapy in cases of tendinitis and muscle strain from overexertion or repetitive strain injuries. Some patients have found it helpful while others have not seen improvement. The advantage of ultrasound, in spite of its varying results on a patient-by-patient basis, is that there is no disadvantage to use it, nor any complications from it, so it is often included in strategies for a combined approach to tendonitis and myositis.
Prevention of Venous Disease Using Ultrasound
Prevention of venous disease using ultrasound is based on two strategies:
- Prevention of initial diseases by screening
- Prevention of disease progression
Prevention of Initial Disease: Screening
Those at risk for venous disease such as venous stasis, venous insufficiency, and thrombosis and embolic potential can be identified via an in depth history and a thorough physical exam. As such, screening of patients at risk for the initial onset of venous disease is indicated in the following groups:
- Obese patients
- Immobilized patients
- Patients with a family history of coagulation conditions
- Patients with a history of trauma to the extremities
Prevention of Disease Progression
Once diagnosed, those with venous disease, especially those suffering from thrombosis or ulceration should have treatment immediately. Whatever therapy is implemented, from conservative medical management (compression, elevation, and ulcer care) to anticoagulation to vein ablation or removal, ultrasound can be used to judge the efficacy of therapy and when indicated, direct a change in treatment protocols after previous therapy has failed.