Incidence. DVT affects >2.5 million people each year in the United States. This is likely an underestimate as many cases go unrecognized by patient and physician. Series have shown the incidence of DVT to be as high as 65% in the untreated major trauma patient.

Risk factors. In general, these include age >75, immobilization, acute infectious disease, cancer, general anesthesia, major surgery, estrogen therapy, pregnancy, prior DVT, congestive heart failure, malignancy, hypercoagulable state, and tissue trauma. Specific to trauma, risk factors include advanced age, lower extremity fracture, spinal cord injury, head injury (AIS >3), ventilator days >3, shock, multiple blood transfusions, surgery, fracture of the femur or tibia, complex pelvic fracture, venous injury, immobility, and spinal cord injury. Scoring systems have been developed to assess risk factors and better estimate the risk of DVT or pulmonary embolism (PE) (Table 16-1).

Location. DVT can occur in any deep venous system.

Local complications. Although rare, local ramifications of DVT include phlegmasia cerulea dolens (edematous, bluish extremity) or phlegmasia alba dolens
(blanching “milk leg”) with potential ulceration, loss of arterial flow, and/or resultant venous gangrene.

Pulmonary embolism. Incidence of pulmonary embolism after trauma varies with population, injury pattern, use of prophylaxis, and method of detection. Overall, 1% to 2% of patients with DVT after trauma will have a pulmonary embolism which carries a 30% to 50% mortality risk.

Postphlebitic syndrome. Venous valves in the lower extremities are destroyed by clot formation when DVT occurs. After the clot dissolves, valvular competence is permanently lost in the affected segment of vein. As a result, nonpitting edema, swelling, discoloration, and pain frequently occur, which can progress to venous hypertension and venous stasis ulceration. The incidence of postphlebitic changes at 12 years post-DVT approximates 28%. Severe sequelae occur in less than 6%.

Clinical manifestation. Subjective complaints of pain or swelling of the affected extremity are rare. In fact, only 40% of patients have any clinical signs or symptoms. The classic syndrome of calf discomfort, edema, venous distension, and pain on dorsiflexion of the foot (Homans’ sign) is seen in less than 30% of patients.

D-dimer. D-dimers are a breakdown product of fibrin and should be elevated when venous thrombosis is present. Fibrin degradation products are elevated in

the first 48 hours after traumatic injury. Therefore, there is little utility in using admission d-dimer to diagnose DVT in the trauma patient.

Compression ultrasound. Duplex ultrasound (DUS) combines real-time B-mode ultrasound with pulsed Doppler capability. In symptomatic patients, the sensitivity and specificity are greater than 95%; thus, DUS is the most commonly performed test for the detection of infrainguinal DVT. The addition of color flow imaging reveals physiologic flow characteristics and may be useful in technically challenging examinations. Whether ultrasound is performed with flow assessment or not, compression of the vein along its length is the key aspect in evaluation for DVT. Noncompressibility of the vein is the primary diagnostic criterion for acute DVT. Other DUS findings include an echogenic thrombus within the vein lumen, venous distension, complete absence of spectral or color Doppler signal from the vein lumen, or loss of flow phasicity, response to Valsalva, or augmentation. Limitations of DUS include patient characteristics (obesity, edema, or tenderness), inability to ultrasound through various devices (casts, etc.) or compression of a vein by perivenous pathology (tumor, hematoma). In addition, DUS is unreliable in evaluating iliac veins.

Contrast venography. While contrast venography (CV) remains the gold standard for diagnosis of DVT, it is rarely used due to the accuracy of noninvasive testing. CV is invasive and requires intravenous injection of contrast dye with the risks associated; however, it is considered to be 100% sensitive and specific. Diagnosis requires a constant intraluminal filling defect in two views or an abrupt cutoff of a deep vein.

CT venography (CTV). CTV uses venous phase contrast to directly visualize the inferior vena cava, pelvic veins, and lower extremity veins. It can be timed immediately after a CT pulmonary angiogram (CTPA) or used alone; however, when combined with CTPA, many series report a higher IV contrast dose is necessary for accurate visualization of the vessels. CTV can be plagued by artifact, such as from orthopedic hardware, or poor venous enhancement. The sensitivity and specificity are 89% to 100% and 94% to 100%, respectively. Some advantages of CTV are the readily available of CT scan in most hospitals at off-hours and the ability of a single study to diagnose both PE and DVT.