| Homepage | Imprint |
|
||
 |
Deep vein thrombosis
Deep-vein thrombosis, also known as deep-venous thrombosis or DVT, is the formation of a blood clot("thrombus") in a deep vein. It commonly affects the legveins, such as the femoral veinor the popliteal veinor the deep veins of the pelvis. Occasionally the veins of the armare affected (known as Paget-Schrötter disease). Thrombophlebitisis the more general class of pathologies of this kind.
Signs and symptomsThere may be no symptoms referrable to the location of the DVT, but the classical symptoms of DVT include pain, swellingand redness of the legand dilatation of the surface veins. In up to 25% of all hospitalised patients, there may be some form of DVT, which often remains clinically inapparent (unless pulmonary embolismdevelops). There are several techniques during physical examination to increase the detection of DVT. These include measuring the circumference of the affected and the contralateral limb at a fixed point (to objectivate edema), and palpating the venoustract, which is often tender. Physical examination is unreliable for excluding the diagnosis of deep vein thrombosis. A careful history has to be taken considering risk factors (see below), including the use of the oral contraceptive pill, recent long-haul flying, a history of miscarriage(which is a feature of several disorders that can also cause thrombosis). A family history can reveal a hereditaryfactor in the development of DVT. It is vital that the possibility of pulmonary embolismis included in the history, as this may warrant further investigation (see pulmonary embolism). DiagnosisIn a low-probability situation, current practice is to commence investigations by testing for D-dimerlevels. This fibrin degradation productis an indication that thrombosisis occurring, and that the blood clotis being dissolved by plasmin. A low D dimer level should prompt other possible diagnoses (such as a ruptured Baker's cyst, if this has not been considered as part of the history). Other blood tests usually performed at this point are:
Compression ultrasoundscanning of the leg veins, combined with duplex measurements (to determine blood flow), can reveal a blood clotand the extent of it (i.e. whether it is below or above the knee) is often used to complement the above tests. The gold standardis intravenous venography, which involves injecting a peripheral veinof the affected limb with a contrast agentand taking X-rays, to reveal whether the venoussupply has been obstructed. Because of its invasiveness, this test is rarely performed. Impedance plethysmographycan also be used as a non-invasive alternative. TherapyAnticoagulationis the usual treatment for DVT. Thrombolysisis generally reserved for extensive clot, e.g. an iliofemoral thrombosis. In general, patients are initiated on a brief course (i.e., less than a week) of heparintreatment, while they start on a 3- to 6-month course of warfarin(or related vitamin Kinhibitors). Low-molecular-weight heparin(LMWH) is the type of heparin generally used, though unfractionated heparinis given in patients who have a contraindication to LMWH (e.g., renal failure or imminent need for invasive procedure). In patients who have had recurrent DVTs (two or more), anticoagulation is generally "life-long." In patients who cannot have anticoagulant treatment (e.g., cerebral hemorrhage) or those who have recurrent PEs while on anticoagulation, an inferior vena cava filter(also referred to as a Greenfield filter) may prevent pulmonary embolisation of the leg clot. However these filters are themselves potential foci of thrombosis, IVC filters are viewed as a temporizing measure for preventing life threatening pulmonary embolism. ProphylaxisIn 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. Intermittent pneumatic compression(IPC) machines 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 arternately 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. Pathogenesis
Thrombosis is a multifactorial process, caused by the nature of blood flow, the consistency of the blood, and qualities of the vessel wall (Virchow's triad). Among the plethora of risk factors, immobilisation, female gender, use of oral contraceptivesand air travel("economy class syndrome") are some of the better-known causes. Thrombophilia(tendency to develop thrombosis) often expresses itself with recurrent thromboses. It is recognised 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 poplitealvein. Very extensive DVTs can extend into the iliac veinsor the inferior vena cava. The risk of pulmonary embolism is higher in more extensive clots. EpidemiologyDVT's occur in about 1 per 1000 persons per year. About 1-5% will die from the complications (i.e. pulmonary embolism). External links
nl:Diep-veneuze trombose
| ||||||||||||||||||||||||||
