Surveillance of Deep Vein Thrombosis DVT

Rajan Gupta and Jeffrey Carpenter Introduction

The clinical evaluation of the peripheral venous system can be difficult. History and physical examination have a limited role in the accurate diagnosis of venous disease. Further diagnostic imaging is frequently required. Invasive techniques such as venography have been proven to be reliable and have become the "gold standard" against which all other techniques are measured. However, the expense and potential risks of such invasive studies have led to the development of noninvasive methods. Through recent technological advancements, ultrasound has emerged as a reliable and useful tool in the evaluation of the peripheral venous system. Its accuracy approaches that of venography, and its other benefits including portability and fewer potential risks have made it an attractive alternative to the "gold standard".

One of the most common manifestations of peripheral venous disease in surgical patients is venous thromboembolism. It is a dreaded complication seen in every surgical specialty; however, certain patient populations have been identified that seem to be at greater risk. The morbidity and mortality associated with this disease process have been well described. Intuitively, many of these patients are sicker and often are found in critical care units. Thus, many studies have examined the role of aggressive measures to prevent this serious complication in these potentially critically ill patients. The use of various interventions including pharmaceutical agents, mechanical devices, and early mobilization has been well established. Some studies advocate routine screening in select populations considered to be at extremely high risk for venous thromboembolism. The imaging modality most commonly used for this routine screening has been ultrasound. This chapter will review the role of ultrasound in screening and diagnosing this peripheral venous disease in select surgical patients. It will also review some of the important technical concepts in performing and interpreting an adequate study.

History and Indications

Venous thromboembolism is often clinically silent, and physical examination is an insensitive tool in the diagnosis of this disease. Several studies have demonstrated a relatively high incidence of occult deep venous thrombosis (DVT) and pulmonary embolus (PE) in select patients. This underscores the necessity for prophylaxis in these select patients. The 5th American College of Chest Physicians (ACCP) Consensus Conference on Antithrombotic Therapy report on the prevention of venous thromboembolism identifies risk factors and patient groups considered to be at high risk.1 Any surgical procedure or disease process that exposes the patient to any of the risk factors described by Virchow's triad of stasis, endothelial damage, and hyperco-agulability places that patient in a high risk population. Patients undergoing major surgery to the abdomen, pelvis, and lower extremities, as well as patients with congestive heart failure, myocardial infarction, stroke, and fractures of the pelvis and lower extremities are all at risk for prolonged immobility. Prior venous thrombosis and the presence of indwelling venous catheters result in endothelial damage and increase the risk of further thromboembolism. Many clinical conditions predispose patients to a hypercoaguable state. Among these are the presence of cancer, estrogen use, and several hemostatic abnormalities including lupus anticoagulant, protein C and protein S deficiencies, antithrombin III deficiency, and factor V Leiden mutation. The ACCP Consensus Conference report cites the incidence of DVT in general surgery patients to be as high as 29%, and the incidence of PE to be as high as 1.6% (fatal PE: 0.9%). Current recommendations for prophylaxis include the use of low dose unfractionated heparin (LDUH), low molecular weight heparin (LMWH), or intermittent pneumatic compression devices (IPC). In patients undergoing orthopedic surgery for total hip or knee replacement as well as hip fracture, the incidence of DVT and PE are significantly higher (84% and 24% respectively). Current recommendations for prophylaxis include LMWH or warfarin. The incidence of DVT in patients suffering from myocardial infarction or stroke was noted to be as high as 24% for MI and 63% for stroke. Either full anticoagulation or LDUH is recommended for prophylaxis in patients with MI. For patients with stroke, both LDUH and LMWH are effective.

Patients sustaining multiple traumatic injuries often have a combination of prolonged immobility, endothelial injury, and a hypercoaguable state. This places trauma patients at significant risk for thromboembolic complications. A recent study demonstrated an incidence of 58% for all DVT and 18% for proximal DVT in 349 trauma patients.2 Other studies have cited the incidence of fatal PE to be as high as 2%, and PE is the third most common cause of death in trauma patients who survive beyond the first day. Additionally, thromboembolic complications account for up to 9% of hospital readmissions following trauma. The incidence of post throm-botic syndrome is cited to be as high as 23%. Thus, an aggressive approach to the prevention and detection of DVT and PE in this select population appears to be warranted. A large prospective, randomized study compared the efficacy and safety of LDUH versus LMWH in select adult trauma patients.3 Patients receiving LDUH had a significantly higher incidence of all DVT as well as proximal DVT. There was no significant difference in bleeding complications. Thus current recommendations from the ACCP Consensus Conference report suggest the use of LMWH in trauma patients unless contraindicated. Mechanical (IPC) devices are recommended for patients who cannot be anticoagulated.

Several studies have attempted to identify subsets of trauma patients that are at extremely high risk for venous thromboembolic complications. Patients with spinal cord injury, traumatic brain injury, pelvic and lower extremity fractures, advanced age, and either venous injury or indwelling venous catheters are at significantly increased risk. Many groups have advocated the use of surveillance ultrasound in this population to detect clinically occult DVT. Knudson and colleagues followed 251 trauma patients with serial duplex exams.4 They noted an incidence of 6% for lower extremity DVT, of which the majority were clinically silent. Through risk factor analysis in their own patient cohort as well as a review of the existing literature, they identified the injury patterns listed above as factors that significantly increase the risk of thromboembolism. They concluded that surveillance with serial ultrasound exams in these patients allowed for prompt recognition and treatment of occult

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