Thrombosis in the veins as described above is caused by three underlying mechanisms (venostasis, vessel wall inflammation and hypercoagulability) called as Virchows's triad. DVT can occur at several places. DVT in lower limbs always starts in calf veins and propagates above knees in majority of symptomatic patients even before the diagnosis is suspected. It has been shown that practically every patient with DVT in upper thigh will develop PE. The popliteal segment of the femoral vein is culprit in 80 per cent of cases. DVT can occur in pelvic veins in post partum females.It can also occur in upper arm (axillary or subclavian) veins due to indwelling catheters and central venous lines inserted for treating sick patients.
The diagnosis of DVT is missed many a times and patient can directly present with PE. The clinical diagnosis of DVT is possible if a strong suspicion is kept in mind in all patients predisposed to it (Table ). Swelling of one or both legs, calf pains (tenderness), pain in legs on walking or fever can be presenting symptoms. D - dimer blood assay can be helpful in diagnosis as discussed subsequently.The detection of DVT has been facilitated in recent years due to availability of several diagnostic modalities e.g.: venous ultrasound, plethysmography, computed tomographic (CT) venography, conventioilal venography and magnetic resonance venography (MRV) and D-dimer blood test.
Duplex ultrasound including both gray scale and Doppler imaging examination of lower extremity venous system has become the most widely utilized modality for diagnosis and exclusion of DVT. This technique is-widely available, inexpensive, canbe performed at bed side, is safe and rapidly provides an accurate diagnosis of proximal vein DVT in 90 per cent of patients. Duplex ultrasound has replaced impedance plethysmography and considerably reduced the need for contrast venography. The techrical quality of examillation depends on operator skill. The other limitation of ultrasound is that it allows only a limited assessment of pelvic and calf veins.
Computed tomographic venography (CTV) is a new modality. In advanced centers, a single examination capable of evaluating both the pulmonary arterial system, pelvic and lower extremity venous system is utilized for diagnosing VTE. It offers distinct advantages over other tests. First CT angiography of pulmonary arteries is performed and then venous angiography is carried out. CTV provides direct imaging of the inferior vena cava, pelvic and lower extremity veins. This is an expensive test. Similarity, M1CV is another new and expensive modality which is available in some advanced centers. MRV also shares with CTV the advantages of better delineation of
the venous anatomy.Catheter based contrast venography still remains a useful test for patients in whom ultrasound imaging is of poor quality. It is also req;ired in those patients where catheter directed thrombolysis or iilterve~ltions or a surgical procedure is necessary.
Prevention
The best way to treat DVT is to prevent it. The prevention of DVT can be accomplished by early mobilization following any illness, surgical procedure, by promoting early physiotherapy, use of compression stockings and by administering prophylactic low molecular weight heparin. Table 3.3 lists the situations where VTE prophylaxis using heparin is indicated. Table 3.4 shows"t11e dosage schedule of low molecular weight hepain recommended for prevention of DVT.
The diagnosis of DVT is missed many a times and patient can directly present with PE. The clinical diagnosis of DVT is possible if a strong suspicion is kept in mind in all patients predisposed to it (Table ). Swelling of one or both legs, calf pains (tenderness), pain in legs on walking or fever can be presenting symptoms. D - dimer blood assay can be helpful in diagnosis as discussed subsequently.The detection of DVT has been facilitated in recent years due to availability of several diagnostic modalities e.g.: venous ultrasound, plethysmography, computed tomographic (CT) venography, conventioilal venography and magnetic resonance venography (MRV) and D-dimer blood test.
Duplex ultrasound including both gray scale and Doppler imaging examination of lower extremity venous system has become the most widely utilized modality for diagnosis and exclusion of DVT. This technique is-widely available, inexpensive, canbe performed at bed side, is safe and rapidly provides an accurate diagnosis of proximal vein DVT in 90 per cent of patients. Duplex ultrasound has replaced impedance plethysmography and considerably reduced the need for contrast venography. The techrical quality of examillation depends on operator skill. The other limitation of ultrasound is that it allows only a limited assessment of pelvic and calf veins.
Computed tomographic venography (CTV) is a new modality. In advanced centers, a single examination capable of evaluating both the pulmonary arterial system, pelvic and lower extremity venous system is utilized for diagnosing VTE. It offers distinct advantages over other tests. First CT angiography of pulmonary arteries is performed and then venous angiography is carried out. CTV provides direct imaging of the inferior vena cava, pelvic and lower extremity veins. This is an expensive test. Similarity, M1CV is another new and expensive modality which is available in some advanced centers. MRV also shares with CTV the advantages of better delineation of
the venous anatomy.Catheter based contrast venography still remains a useful test for patients in whom ultrasound imaging is of poor quality. It is also req;ired in those patients where catheter directed thrombolysis or iilterve~ltions or a surgical procedure is necessary.
Prevention
The best way to treat DVT is to prevent it. The prevention of DVT can be accomplished by early mobilization following any illness, surgical procedure, by promoting early physiotherapy, use of compression stockings and by administering prophylactic low molecular weight heparin. Table 3.3 lists the situations where VTE prophylaxis using heparin is indicated. Table 3.4 shows"t11e dosage schedule of low molecular weight hepain recommended for prevention of DVT.
Treatment of DVT
There are four major goals of therapy for DVT, each of which is directed at the clinical sequale of the disease. Therapy is undertaken to: diminish the severity and duration of lower extremity symptoms, prevent PE, minimize the risk of recurrent venous thrombosis and prevent the post thrombotic syndrome.The treatment consists of symptomatic treatment during acute stage, canticoagulation(short term and long term) and rarely thrombolytic therapy or surgery. There is ample data in the literature to support that anticoagulation provides symptomatic relief,reduces the incidence of PE, recurrent VTE and also reduces long term sequale.
During the active stage of DVT elevation and rest of an acutely swollen leg may provide initial symptomatic relief. Analgesics, anti-inflammatory drugs and antibiotics may be required. The role of absolute bed rest is debatable as it is shown to be associated with increased throinbus propagation and does not appear to reduce the rate of PE. Early mobilization also may lead to resolution of pain and swelling.Therefore routine bed rest should not be recommended as part of standard care for patients with DVT. The advice should be individualized depending on the patient's condition.
The main stay of treatment of VTE (both DVT and PE) remains anticoagulation using either unfiactionated heycarin (UFH) or low molecular weight heparin (LMWH). The protocols for treatment by heparin for DVT and VTE are similar and will be discussed subsequently in details under trealment of PE (also see Table ).Thrombolytic therapy has been shown to provide faster clot dissolution but is associated with higher incidence of bleeding as compared to heparin. This therapy is advocaled only in some cases presellting with either life threatening limb ischemia or severe proximal DVT. Surgical thrombeclomy is also indicated rarely in those patients with contraindication to thrombolysis or in presence of life threatening limb ischemia.
Clinical Features
PE is a common and potentially lethal condition which often remains undetected. A strong clinical suspicion is essential particularly in patients with risk factors to make a correct diagnosis. Clinical suspicion of PE is of paramount importance in guiding diagnostic testing. Dyspnea is the most frequent symptom, and tachypnea is the most frequent sign of PE. In general, severe dyspnea, syncope, shock or cyanosis portends a major life-threatening PE. Rarely, the presentation can be with sudden death.
PE is a common and potentially lethal condition which often remains undetected. A strong clinical suspicion is essential particularly in patients with risk factors to make a correct diagnosis. Clinical suspicion of PE is of paramount importance in guiding diagnostic testing. Dyspnea is the most frequent symptom, and tachypnea is the most frequent sign of PE. In general, severe dyspnea, syncope, shock or cyanosis portends a major life-threatening PE. Rarely, the presentation can be with sudden death.
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