Current Concepts With DVT Prophylaxis
Another article from 2009 analyzed 7,264 patients who underwent podiatric surgery and identified a 0.3 percent rate of VTE (DVT and pulmonary embolism).8 The authors identified three statistically significant risk factors in this study: prior history of VTE, use of hormone replacement therapy or oral contraceptives, and obesity. The authors of this study concluded that routine prophylaxis is not warranted with the possible exception of patients with two or more risk factors. These authors underscore the need for further prospective studies. At this time, there is no evidence-based consensus as to when a patient does or does not require DVT prophylaxis after foot and ankle surgery.
Weighing The Options For Prophylaxis
Options for DVT prophylaxis include both mechanical and pharmaceutical means. The simplest method of prophylaxis is early active range of motion of both the ankle and the toes. This allows the muscles of the gastroc-soleus complex as well as the deep posterior compartment of the leg to function as a musculovenous pump to minimize stasis within the deep veins of the lower extremity.
Sequential compression devices serve to mimic the action of the muscles to stimulate blood flow through the vasculature of the leg.9 These devices have comparable rates of efficacy to heparin and low molecular weight heparin while incurring very little risk to the patient. However, adherence with these devices is very difficult outside of the hospital setting. Accordingly, compression devices are largely relegated to inpatient use.
Physicians have also had patients take aspirin for the prevention of DVT after surgery although its efficacy is under debate.10 It works by irreversibly inhibiting cyclooxygenase, which, in turn, affects the production of prostaglandins and thromboxane, thus irreversibly inhibiting platelet function. While aspirin is a relatively potent antiplatelet drug, it does not affect the coagulation cascade. Aspirin may also have side effects not related to bleeding. These side effects may include erosion of the gastric lining and exacerbation of asthma in some patients with reactive airway disease. Despite these disadvantages, aspirin has the advantage of PO dosing, minimal cost and ease of availability.9,10
The heparins work by affecting the coagulation cascade directly. Heparin inhibits the action of thrombin and other clotting factors by binding to antithrombin III. Heparin (unfractionated heparin) is available in both subcutaneous and IV administrations. Intravenous dosing is usually reserved for treatment of existing thrombosis while one may use subcutaneous dosing for VTE prophylaxis. Unfractionated heparin has a higher risk of causing heparin-induced thrombocytopenia in comparison with the low molecular weight heparins. The low molecular weight heparins are in more common use than unfractionated heparin for outpatient prevention of DVT due to ease of dosing, the lack of need for monitoring and the availability of pre-packaged self-administration kits.
While heparins can reduce the occurrence of DVT and PE, they also have their own set of disadvantages. The low-molecular weight heparins will require patients to give themselves subcutaneous injections, which may be unacceptable to some patients. There is also potential for the formation of hematomas and bruising at the injection sites.2
Warfarin therapy (Coumadin, Bristol-Myers Squibb) is another form of prophylaxis, which physicians frequently employ if long-term anticoagulation is required. Warfarin is a vitamin K analogue which, when ingested, inhibits the production of the vitamin K dependent factors (II, VII, IX and X) as well as protein C and protein S.