Definition

Venous thromboembolism (VTE) is a major cause of mortality and morbidity and is manifested by deep venous thrombosis (DVT) and pulmonary embolism. This chapter is limited to the discussion of DVT. DVT occurs when a fibrin clot abnormally occludes a vein in the deep venous system, predominantly in the lower extremities. The prevailing theory explaining the development of DVT is known as Virchow triad, which includes alterations in blood flow (stasis), vascular endothelial injury, and hypercoagulation disorder. The risk for development of DVT varies according to specific characteristics of the patient, the medical condition, or the surgical procedure ( Table 128.1 ). Conditions that may increase the risk for development of DVT are advanced age, morbid obesity, varicose veins, prolonged immobility, pregnancy, malignant disease, stroke, inflammatory bowel disease, congestive heart failure, and previous DVT. Certain hereditary conditions may also predispose to development of DVT, such as deficiencies in protein C and protein S and familial thrombophilia. Acquired deficiencies of the natural anticoagulant system include antibodies directed against antiphospholipid and heterozygous factor V Leiden mutations.

Patients can be categorized according to their risk for development of DVT on the basis of the type of surgical procedure, with orthopedic patients carrying the highest risk ( Table 128.2 ). It is believed that orthopedic procedures carry such a high risk for DVT because the mechanical destruction of bone marrow during most orthopedic procedures causes intravasation of marrow cells and cell fragments and elevations of plasma tissue factor. Plasma tissue factor is a potent trigger of blood clotting. It is found in high concentrations in bone marrow and the adventitia surrounding the major blood vessels and the brain. Surgical trauma to these structures places neurosurgical patients at great risk for development of DVT. Following neurosurgery, the incidence of DVT has been reported to be as high as 50%. Risk factors that increase the rates of DVT in neurosurgery patients include intracranial surgery, malignant tumors, duration of the surgery, and presence of paresis or paralysis of the lower limbs. Patients can remain in a hypercoagulable state up to 5 weeks postoperatively. In addition to surgical patients, victims of orthopedic and neurologic trauma are at great risk for development of DVT, especially if long bone fracture or paralysis is sustained. Patients who suffer injury to the spinal cord are at high risk for DVT because of stasis and hypercoagulability.

Symptoms

Venous thrombosis often occurs asymptomatically. Symptoms of DVT may include ipsilateral lower extremity edema, fever, extremity warmth, and pain. Symptoms do not rule in or rule out DVT, but they can serve as a trigger for further diagnostic inquiry.

Physical Examination

The classic signs of DVT are tenderness, ipsilateral swelling, and warmth. A palpable cord can sometimes be felt, indicative of a thrombosed vein. In the past, emphasis was placed on the presence of Homan’s sign and calf tenderness in making a clinical diagnosis of DVT. However, these physical examination findings have been found to be nonspecific with poor positive predictive values. Significant asymmetric calf edema is an important sign and can be determined by taking the circumferential measurement of the calf 10 cm below the tibial tuberosity. A 3-cm difference in calf girth is considered a significant clinical difference. When it is massive, the swelling can obstruct not only venous outflow but also arterial inflow, leading to phlegmasia cerulea dolens as a result of ischemia. Here, the leg is usually blue and painful.

As with symptoms, physical examination findings are neither sensitive nor specific. In more than 50% of the instances of DVT, physical examination findings are normal.

Functional Limitations

DVT rarely causes functional compromise, except calf pain during walking. Absolute bed rest is generally not indicated, and early walking is safe in patients with acute DVT and may help reduce acute symptoms. However, patients should suspend their lower extremity exercise program until they are fully anticoagulated.

Diagnostic Studies

The Wells clinical prediction rule ( Table 128.3 ) is a score based on a group of clinical characteristics that are useful in estimating the pretest probability of DVT. High-quality evidence exists to support the validity of this rule, and its use is recommended as a practice guideline by the American Academy of Family Physicians and the American College of Physicians. It is easily implemented before more definitive testing is performed on patients.

Table 128.3

Wells Prediction Rules: Clinical Evaluation Table for Predicting Pretest Probability of Deep Venous Thrombosis

Clinical Characteristic	Score
Active cancer (treatment ongoing, within previous 6 months, or palliative)	1
Paralysis, paresis, or recent plaster immobilization of the lower extremities	1
Recently bedridden > 3 days or major surgery within 12 weeks requiring general or regional anesthesia	1
Localized tenderness along the distribution of the deep venous system	1
Entire leg swollen	1
Calf swelling 3 cm larger than asymptomatic side (measured 10 cm below tibial tuberosity)	1
Pitting edema confined to the symptomatic leg	1
Collateral superficial veins (nonvaricose)	1
Alternative diagnosis at least as likely as deep venous thrombosis	−2

 

Clinical probability: low, ≤ 0; intermediate, 1–2; high, ≥ 3. In patients with symptoms in both legs, the more symptomatic side is used.

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