Prevention of venous thrombosis and pulmonary embolism

Deep vein thrombosis (DVT) leads to hospitalization for up to 600,000 persons each year in the United States. Venous thrombosis in itself may be benign, but the condition can lead to dangerous complications and has a high recurrence rate. Strategies to prevent DVT involve prevention of stasis and reversal of changes in blood coagulability that allow thrombi to form. Pharmacologic agents have been effective in reducing the incidence of DVT and pulmonary embolism. Low-dose subcutaneous heparin is considered a nearly ideal DVT preventative for surgically treated patients. The risk of hemorrhage is the main limitation to routine use of subcutaneous anticoagulants for DVT, but careful patient selection can minimize that risk. After anticoagulant therapy with heparin, generally for 7 to 10 days, oral warfarin is the drug of choice for maintenance anticoagulation to prevent DVT recurrence. Therapy for pulmonary embolism is the same as for DVT--immediate anticoagulation with heparin followed by maintenance with warfarin.     

Diagnosis of venous thrombosis and pulmonary embolism

Venous thrombosis and pulmonary embolism are closely related disorders. As many as 70 to 80% of patients with pulmonary embolism have associated proximal deep venous thrombosis. The clinical diagnosis alone of both venous thrombosis and pulmonary embolism is inaccurate because of the insensitivity and nonspecificity of findings, a problem that also occurs with a variety of other disorders. Invasive, objective tests are still the reference standard, but they are not always easy to perform, they cannot be used for a considerable number of very ill patients, and they create some patient discomfort. There is an increasing trend toward using noninvasive methods, either alone or in combination. These methods entail less risk, can be performed more quickly and conveniently, and are usually more cost-effective. Practical approaches to diagnosing venous thrombosis and pulmonary embolism in the clinical setting are discussed.     

Heparin therapy for venous thrombosis and pulmonary embolism

Intravenous heparin is the initial treatment of choice for most patients with acute pulmonary embolism or proximal deep vein thrombosis. The primary objective of initial heparin therapy in such patients is to prevent recurrent venous thromboembolism. The efficacy of intravenous heparin for this purpose has been established by randomized clinical trials in patients with pulmonary embolism, and more recently, in patients with proximal vein thrombosis. Heparin is given as an initial intravenous bolus of 5000 units, followed by a maintenance dose of 30,000-40,000 units per 24 h by continuous intravenous infusion. A recent randomized trial in patients with proximal vein thrombosis indicates that failure to achieve an adequate anticoagulant response (APTT greater than 1.5 times control) is associated with a high risk (25%) of recurrent venous thromboembolism. Intravenous heparin administered in doses that prolong the activated partial thromboplastin time (APTT) to 1.5 or more times the control value is highly effective, and associated with a low frequency (2%) of recurrent venous thromboembolism. Heparin is continued for 7-10 days, overlapped with warfarin sodium during the last 4-5 days. Multiple randomized clinical trials indicate that this approach is highly effective. An alternative approach is to commence heparin and oral anticoagulants together at the time of diagnosis, and to discontinue heparin on the fourth or fifth day. A recent randomized trial in patients with submassive venous thrombosis or pulmonary embolism suggests that 4-5 days of initial heparin therapy is effective and safe, but this approach must be evaluated by further randomized trials before it is recommended for patients with extensive proximal vein thrombosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Incidence of pulmonary embolism in deep venous thrombosis

Abnormal radionuclide phlebograms were found in 65 patients in whom simultaneous-perfusion lung scintigrams and phlebograms were performed. All these patients were on adequate treatment with heparin for deep venous thrombosis. In 28% of the cases, the diagnosis of pulmonary embolism was made because they had abnormal perfusion lung scans with normal chest radiograph and clinical symptoms of pulmonary embolism.     

Deep venous thrombosis and pulmonary embolism in pregnancy.

Deep venous thrombosis and pulmonary embolism are relatively frequent occurrences in pregnancy and the postpartum period. The diagnosis of deep venous thrombosis and pulmonary embolism requires accurate objective tests because clinical diagnosis is unreliable. Procedures that expose the fetus to ionizing radiation must sometimes be performed to make an accurate diagnosis; current evidence suggests that the adverse effects to the fetus associated with such procedures are minimal. Heparin is the anticoagulant of choice during pregnancy and is used for both the treatment and prevention of venous thrombosis and pulmonary embolism. Patients with deficiencies of antithrombin III, protein C, or protein S as well as patients with antiphospholipid antibodies are at increased risk for thrombotic complications and require particular vigilance during pregnancy.     

Heparin kinetics in venous thrombosis and pulmonary embolism.

The response to a standard dose of heparin was studied in 20 patients with venous thromboembolism. The heparin regimen consisted of intravenous injection of 70 units per kg, followed after 90 minutes by a maintenance dose of 400 units per kg per 24 hours given by continuous infusion. Plasma heparin activity and the activated partial thromboplastin time (APTT) were measured at intervals to determine clearance of the initial injection and the response to maintenance dose. Large inter-individual variations were found in the anticoagulant effect and these were due in part to differences in heparin clearance and in part to differences in the APTT response to given amounts of heparin (heparin effect index). The heparin half-life was 63 +/- 15 minutes when plasma heparin activities were used for this calculation and 84 +/- 71.5 minutes when the APTT was used. These results are similar to values previously reported in normal volunteers. Four of the 20 patients had pulmonary embolism and in these heparin half-life was significantly shortened (P less than 0.005).     

Deep venous thrombosis and pulmonary embolism following cardiac catheterization

We report 4 cases of deep venous thrombosis and/or pulmonary embolism after diagnostic cardiac catheterization. Two of these cases followed left heart catheterization alone.© 1993 Wlley-Liss, Inc     

Right atrial thrombosis and severe pulmonary embolism]

Two cases of severe pulmonary embolism associated with right atrial thrombosis are reported. In the first case, fibrinolytic therapy was administered and was thought to be a causative factor in the death of the patient due to massive pulmonary embolism. In the second case, the patient was referred for surgery and two enormous thrombi were extracted. Unfortunately, the outcome was fatal. These two cases were confronted with the results of the literature. They strongly suggest that echocardiography should be a first-line investigation in severe pulmonary embolism. The detection of right atrial thrombosis modifies the clinical strategy and orientates treatment towards surgical referral when the patient's condition allows it.     

Prevention of venous thrombosis and pulmonary embolism following orthopedic surgery

This is a literature review on prevention of deep vein thrombosis and pulmonary embolism. Criteria for clinical trials are listed, diagnostic techniques are discussed, and nine approaches for preventing venous thromboembolism are outlined. Choices for primary prophylaxis in hip surgery and major knee surgery are presented.     

Diagnosis of deep venous thrombosis and pulmonary embolism in pregnancy.

Accurate diagnosis of deep venous thrombosis and pulmonary embolism is required because treatment can be lifesaving, although inappropriate anticoagulation exposes the mother and fetus to hemorrhage and other hazards. Clinicians must be aware of which patients are at risk, as deep venous thrombosis is frequently asymptomatic. Clinical diagnosis is unreliable for deep venous thrombosis and pulmonary thromboembolism; therefore, objective tests are required. Venography is the gold standard test for deep venous thrombosis but is invasive. It has been superseded by less invasive tests such as compression ultrasound. This test, although not yet rigorously scrutinized in pregnancy, is now the first-line investigation. Where doubt remains, venography, CT, and magnetic resonance imaging have a role. Ventilation-perfusion scanning is the pivotal test for pulmonary thromboembolism for pregnancy, and it need not expose the fetus to excess radiation. If the results of this test are unclear, deep venous ultrasound can guide management of suspected pulmonary thromboembolism, thus avoiding pulmonary angiography.     

Upper-extremity deep venous thrombosis and pulmonary embolism. A prospective study

We prospectively evaluated the prevalence of pulmonary embolism (PE) in 30 consecutive patients with proved deep venous thrombosis (DVT) of the upper extremity. Ten patients (seven male and three female; mean age, 43 years) had primary DVT, and 20 patients (14 male and six female; mean age, 52 years) had catheter-related DVT. Ventilation-perfusion lung scans were routinely performed at the time of hospital admission to all but one patient (one patient was critically ill, and he died four days after DVT diagnosis because of massive PE). Lung scan findings were normal in nine of ten patients with primary DVT, and they were indetermine in the remaining patient. By contrast, perfusion defects were considered highly suggestive of PE in four patients with catheter-related DVT; two patients had indeterminate lung scans, and 13 patients had normal scans. We conclude that PE is not a rare complication in upper extremity DVT, and that patients with catheter-related DVT seem to be at a higher risk.     

Approaches to deep venous thrombosis and pulmonary embolism in aging patients

Deep venous thrombosis and its complication, pulmonary embolism, are common clinical problems in the elderly and are responsible for significant morbidity and mortality. Diagnosis on clinical grounds alone is notoriously unreliable, and objective tests are necessary to avoid overtreatment or undertreatment. Etiology, clinical evaluation and testing, diagnostic strategies, and prophylaxis are reviewed to present a current perspective on this serious problem.     

Prevention of deep venous thrombosis and pulmonary embolism in general surgery

Among the various methods to diagnose deep venous thrombosis in the lower limbs, the radiofibrinogen uptake test has been mainly used in clinical studies. Physical means to accelerate venous return are of limited use and only in patients at a low thrombotic risk. Antivitamins K are efficient, but surgeons hesitate to use them because of the postoperative hemorrhagic risk. Dextran infusions are quite effective and without real risk of bleeding. The same holds for low dose heparin administered subcutaneously, particularly when combined with dihydroergotamine. Among the various anti-aggregating agents only aspirin may be effective in the prevention of venous thrombosis.