Chapter 26

Duplex ultrasound examination of the peripheral arterial and venous systems has been refined to the point where it has become the initial modality of choice for vascular diagnosis. Technical advances have improved diagnostic accuracy such that treatment decisions previously based on angiographic studies can now be based solely on noninvasive studies. This is most evident in the noninvasive diagnosis of deep venous thrombosis (DVT),1 and is becoming more prevalent in the management of carotid occlusive disease and atherosclerotic peripheral vascular disease.

Risk factors associated with the development of DVT are common in the critical care setting. Virchow's triad of stasis, endothelial injury, and altered coagulation are readily seen in today's intensive care unit (ICU). Clinical factors such as major trauma, which include neurological injury, pelvic and long bone fractures2,3; prolonged immobilization due to altered mental status, paralysis, morbid obesity; multiple sites for venous access and central monitoring; and advancing age, all contribute to this increased risk.4

The true prevalence of acute DVT in the ICU setting is unknown. Reported incidence varies widely (4–60%) due to patient population, detection methods, and the application of surveillance programs.57 Despite increased awareness and aggressive application of protocols for the prevention of DVT, postmortem studies indicate that subclinical, undetected DVT and pulmonary embolism (PE) continue to exist.8 In addition, many ICU patients are at risk for rebleeding and are not candidates for anticoagulation.

Invasive hemodynamic monitoring or prolonged central venous access is common in the critical care environment. Catheter-associated thrombosis occurs in response to endothelial injury and the alterations in normal venous flow patterns caused by the catheter. This may be more significant in children, where small diameter veins can be functionally occluded by catheterization.9

Although the most common sequelae of DVT are the late problems of venous insufficiency and stasis ulceration, PE is the primary concern in the acute care setting. The present emphasis on DVT prophylaxis arises from the recognition that PE is one of the most preventable causes of death and major morbidity in hospitalized patients. Because most clinically significant PE arises from deep veins of the lower extremities, some centers have advocated routine duplex ultrasound surveillance of patients during their ICU stay.

Continuous-wave Doppler ultrasound technology was introduced to clinical practice in the 1970s. Although no images were possible, these devices allowed the examiner to assess venous flow patterns by auditory waveform analysis. The combination of ultrasound imaging and Doppler spectral analysis provided the basis for current duplex ultrasound technology. By the early 1990s, the venous duplex ultrasound examination replaced contrast venography as the gold standard for the diagnosis of DVT.

Standard practice requires a trained sonographer to transport the ultrasound machine (portable but bulky) to the ICU, where a full lower extremity examination is performed and recorded on videotape or digital media. The study is reviewed by the ...

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