Deep Vein Thrombosis (DVT)
Deep vein thrombosis (also known as deep venous thrombosis and usually abbreviated as DVT) is the formation of a blood clot in a deep vein. It is a form of thrombophlebitis (inflammation of a vein with clot formation).
There may be no symptoms referable to the location of the DVT, but the classical symptoms of DVT include pain, swelling and redness of the leg and dilation of the surface veins. In up to 25% of all hospitalized patients, there may be some form of DVT, which often remains clinically inapparent (unless pulmonary embolism develops).
There are several techniques during physical examination to increase the detection of DVT, such as measuring the circumference of the affected and the contralateral limb at a fixed point (to objectivate edema), and palpating the venous tract, which is often tender. Physical examination is unreliable for excluding the diagnosis of deep vein thrombosis.
In phlegmasia alba dolens, the leg is pale and cool with a diminished arterial pulse caused by spasm. It usually results from acute occlusion of the iliac and femoral veins because of DVT.
In phlegmasia cerulea dolens, there is an acute and nearly total venous occlusion of the entire extremity outflow, including the iliac and femoral veins. The leg is usually painful, cyanosed (blue from lack of oxygen) and oedematous (filled with fluid). Venous gangrene may supervene.
It is vital that the possibility of pulmonary embolism be included in the history, as this may warrant further investigation (see pulmonary embolism).
A careful history has to be taken considering risk factors, including the use of estrogen-containing methods of hormonal contraception, recent long-haul flying, intravenous drug use and a history of miscarriage (which is a feature of several disorders that can also cause thrombosis). In the case of long-haul flying, recent studies have shown that risk of DVT is higher in travellers who smoke, are obese, or are currently taking contraceptive pills. A family history can reveal a hereditary factor in the development of DVT. Approximately 35 percent of DVT patients have at least one hereditary thrombophilia, including deficiencies in the anticoagulation factors protein C, protein S, antithrombin, or mutations in the factor V and prothrombin genes.
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CAUSES & RISK FACTORS
Virchow's triad is a group of three factors known to affect clot formation: rate of flow, the consistency (thickness) of the blood, and qualities of the vessel wall. Virchow noted that more deep venous thrombosis occurred in the left leg than in the right and proposed compression of the left common iliac vein by the overlying right common iliac artery as the underlying cause.
The most common risk factors are recent surgery or hospitalization. Forty percent of these patients did not receive heparin prophylaxis. Other risk factors include advanced age, obesity, infection, immobilization, use of combined (estrogen-containing) forms of hormonal contraception, tobacco usage and air travel ("economy class syndrome", a combination of immobility and relative dehydration). Thrombophilia (tendency to develop thrombosis) often expresses itself with recurrent thromboses.
It is recognized that thrombi usually develop first in the calf veins, "growing" in the direction of flow of the vein. DVTs are distinguished as being above or below the popliteal vein. Very extensive DVTs can extend into the iliac veins or the inferior vena cava. The risk of pulmonary embolism is higher in the presence of more extensive clots.
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The gold standard is intravenous venography, which involves injecting a peripheral vein of the affected limb with a contrast agent and taking X-rays, to reveal whether the venous supply has been obstructed. Because of its invasiveness, this test is rarely performed.
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General Medical Patients
Regarding general medical inpatients the guidelines state, "In acutely ill medical patients who have been admitted to the hospital with congestive heart failure or severe respiratory disease, or who are confined to bed and have one or more additional risk factors, including active cancer, previous VTE, sepsis, acute neurologic disease, or inflammatory bowel disease, we recommend prophylaxis with low-dose unfractionated heparin-LDUH (Grade 1A) or LMWH (Grade 1A)." Enoxaparin or unfractionated heparin may be used. LMWH may be more effective than unfractionated heparin (UFH). If UFH is used, 5000 U 3 times daily may be more effective.
Since publication of the ACCP guidelines, an additional randomized controlled trial and meta-analysis including the trial have been published. The meta-analysis concluded " Anticoagulant prophylaxis is effective in preventing symptomatic venous thromboembolism during anticoagulant prophylaxis in at-risk hospitalized medical patients. Additional research is needed to determine the risk for venous thromboembolism in these patients after prophylaxis has been stopped." With regards to which patients are at risk, most studies in the meta-analysis were of patients with New York Heart Association Functional Classification (NYHA) III-IV heart failure. Regarding patients at lesser risk of DVT, the trial above and an earlier trial are relevant yet inconclusive.
Since the ACCP guidelines, compression stockings have been studied for preventing clots in stroke patients. In stroke patients, thigh-length stockings are more effective than knee stockings in the nonblinded CLOTS 2 randomized controlled trial while thigh-length stockings were not better than no stockings in the CLOTS 1 nonblinded randomized controlled trial. It is not clear why these two trials conflict.
Chronic renal dialysis patients may be at increased risk of thromboembolism, but randomized controlled trials have not addressed the risk benefit of prophylaxis.
In patients who have undergone surgery, low molecular weight heparins (LMWH) are routinely administered to prevent thrombosis. LMWH can only currently be administered subcutaneously by injection. Prophylaxis for pregnant women who have a history of thrombosis may be limited to LMWH injections or may not be necessary if their risk factors are mainly temporary.
Early and regular ambulation (walking) is a treatment that predates anticoagulants and is still recognized and used today. Walking activates the body's muscle pumps, increasing venous velocity and preventing stasis. IPC devices have proven protective in bed- or chair-ridden patients at very high risk or with contraindications to heparins. IPC machines use air bladders that are wrapped around the thigh and/or calf. The bladders alternately inflate and deflate, squeezing the muscles and increasing blood velocity by as much as 500%. IPC machines have been proven effective on knee and hip surgery patients (a population with a risk as high as 80% with no prophylactic treatment) of developing DVT and PE.
Pregnancy: Hypercoagulability in pregnancy
The risk of deep vein thrombosis is increased in pregnancy because of a physiologically adaptive mechanism of increased hypercoagulability to prevent postpartum hemorrhage. However, when combined with an additional underlying hypercoagulable states, the risk of thrombosis or embolism may become substantial.
While the general consensus among physicians is that the safety of the mother supersedes the safety of the developing fetus, changes in the anticoagulation regimen during pregnancy can be performed to minimize the risks to the developing fetus while maintaining therapeutic levels of anticoagulation in the mother.
The main issue with anticoagulation in pregnancy is that warfarin, the most commonly used anticoagulant in chronic administration, is known to have teratogenic effects on the fetus if administered in early pregnancy.
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