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David H. Harder, M.D., FRCSC, ABOS
Oyama, BC Is DVT prophylaxis necessary? If so, for whom? It is time to re-examine where we are, how we got here and where we should go.
While prophylaxis for high-risk medical conditions is largely managed by internal medicine specialists, an increasing number of trauma and surgical patients are prophylactically being treated in order to prevent DVT, its complications, and its resulting morbidities.
Who are these patients and are they truly at risk for venous thromboembolism (VTE)? If they are at risk, is that risk greater than that of the unwanted effects of prophylaxis? If the benefit of prophylaxis greatly exceeds that of the undesirable effects of such prophylaxis, are we confident that we are applying the best of the available prophylactic protocols?
Clearly, the first step is to better define patients who are at risk.
Our justification for prophylaxis of certain patient groups, e.g., total hip replacement (THR) and total knee replacement (TKR), flows largely from large cohort studies which include wide varieties of patients of varying ages without exploring individual thrombophlebitic diathesis. These studies have concluded that DVT rates following THR and TKR fall somewhere between 45 and 70%. Many of these are in small calf veins and may not be clinically relevant. The incidence of fatal pulmonary embolus is said to be approximately 2% following THR and is accepted to be considerably less than that following TKR. What has not - and urgently must - be clarified is who those patients are that face a high risk for spontaneous clotting. In the absence of such pre-selection, exposing patients with no compelling predisposing risk factors for VTE to anti-coagulation will continue to result in unwarranted morbidity as a consequence of our interference with normal coagulation and fibrinolytic mechanisms.
Attempts to define DVT risk factors have been made, notably by Tubiana and Duparc who, in 1961, published a number of risk factors that included the following:
- Patients over 40 = 3 points
- A history of spontaneous thrombosis = 6 points
- Varicose veins = 2 points
- Obesity = 2 points
- Hip surgery = 4 points
- Intraoperative clinical shock = 1 point
- Immobilization of the operated part = 2 points
If the total exceeded 9 points, anticoagulation was suggested.
That scale was, to my knowledge, never scientifically validated and did not gain wide acceptance.
The lack of reliable guidelines that define those patients at risk has, however, encouraged surgeons to treat entire patient populations prophylacticly.
In my own orthopaedic practice and having performed large numbers of TKR's over many years before it was fashionable to use VTE prophylaxis, not a single patient died of a proven post-operative pulmonary embolus. Only one of my THR patients suffered a proven fatal pulmonary embolus. When routine prophylaxis for all TKR and THR patients became the norm, this, fuelled by fears of litigation, resulted in the establishment of in-hospital treatment protocols that included such prophylaxis.
Table # 1
VTE Prophylactic Techniques | I. Pharmaceutical VTE Prevention
• ASA
• Dextran
• Unfractionated Heparin – usually low dose
• Low molecular weight heparins (various)
• Coumadin
Variations with reference to dosing schedules, dosages and duration are common.
II. Physical Methods
• Elastic Stockings
• Early Mobilization
• Intermittent pneumatic limb compression
- whole leg
- calf
- plantar foot pump | Various regimens for pharmaceutical prophylaxis have continued, often championed by influential physicians with strong opinions (See Table # 1). Each of these forms of treatment comes with its own particular financial and human costs. It is not only the cost of the drugs but also the cost of required laboratory tests, radiographs, ultrasound, as well as the cost of management of complications resulting from such treatment.
Significant increase in blood loss resulting from heparins, including those with low-molecular weight, is not a frivolous complication. It can and does lead to wound complications that include need for reoperation, infection and tissue loss. It can and does result in blood loss that may trigger the administration of homologous blood. Increased bleeding retards postoperative rehabilitation. Fear of bleeding may interfere with the most desirable regional anaesthetic techniques.
In recent years, the darlings of prophylaxis have been the low molecular weight heparins. Many studies supported by pharmaceutical firms attest to their efficacy, but at what cost?
It is important for physicians involved in the management of thrombophlebitic conditions and events as well as those who oversee laboratory investigations for thrombogenic and fibrinolytic factors to develop risk profiles so that only those patients who are at significant risk for VTE receive pharmaceutical prophylaxis.
Table # 2
Incomplete List of Known or Suggested VTE Risk Factors | I. Inherited Risk Factors
a. Thrombogenic
- Antithrombin III deficiency
- Protein C deficiency
- Protein S deficiency
- Dysfibrinogenemia
- Activated Protein C resistance
(due to Factor V Leiden)
- Prothrombin 20210A (the latter 2 are present in approximately 25% of all thrombotic events in the general population and have been reported in up to 50% of pulmonary emboli occurring in total joint replacement patients)
b. Defects in Clot Removal
Disorders of plasminogen and plasminogen activation (elevations in plasminogen activator inhibitor or decreased plasminogen activator)
II. Acquired Risk Factors - Nephrotic Syndrome
- Paroxysmal Nocturnal Hemoglobinuria
- Malignancy
- Stasis (congestive heart failure, myocardial infarct, cardiomyopathy (constrictive pericarditis, anasarca)
- Advancing age
- Estrogen Therapy (HRT)
- Oral contraceptives
- Pregnancy
- Sepsis
- Immobilization
- Stroke
- Polycythemia Rubra Vera and myeloproliferative disorders
- Inflammatory Bowel Disease
- Obesity
- Prior VTE
- Antiphospholipid Antibodies (Antiphospholipid Syndrome) (Anticardiolipin Antibodies and Lupus anticoagulants)
- Major surgery
- Orthopaedic surgery
Other Potential Risk Factors
- Hyperhomocysteinemia
- High levels of Factor VIII (these are present in approximately 10% of all thrombotic events in the population)
- APC resistance in the absence of Factor V Leiden
| In recent years newly discovered and understood risk factors have been added to this list. These include those that are thrombogenic and those that interfere with fibrinolysis (See Table # 2 for a partial list of known or accepted risk factors).
Even if resulting guidelines cannot be scientifically validated in their entirety, a consensus statement defining the patient at risk would be of great value. Without it, we will continue to unne-cessarily treat many patients and continue to incur unnecessary financial and human costs.
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