BALTIMORE — Methods for determining how and when to use pharmacologic and mechanical interventions to prevent venous thromboembolism in surgical patients may remain open to debate, but the need for prophylaxis should not, Dr. Morey A. Blinder said at the annual meeting of the American Society of Plastic Surgeons.
Prophylaxis is underused because many physicians believe that the incidence of deep venous thrombosis (DVT) in hospitalized patients is "too low" to warrant its consideration, said Dr. Blinder of the division of hematology and the department of pathology and immunology at Washington University, St. Louis.
Other physicians voice concerns about bleeding complications—particularly in surgical patients—and about heparin-induced thrombocytopenia, which occurs in 1%–2% of patients on heparin.
"Many clinicians have the sense that venous thrombosis is not a particular problem in their practice," because they have not seen a DVT in one of their patients for several years or may have not known that a patient had a DVT diagnosed a week after surgery by an internist or at the emergency department, Dr. Blinder said.
In the absence of prophylaxis, studies have found a DVT prevalence of 10%–20% in medical patients, 15%–40% in general surgery patients, and about 20%–50% of stroke and orthopedic surgery patients. Even though most patients did not have symptomatic thrombosis in those studies, each patient underwent venography or a fibrinogen uptake procedure. Most series of major procedures in plastic surgery have found a risk of 1%–2% for DVT and/or pulmonary embolism, generally without prophylaxis, he said.
Deficiencies in any of the body's natural anticoagulants, such as antithrombin, protein C, and protein S, lead to a substantial risk of thrombosis. About 5% of people with European heritage carry a mutation in the blood-clotting factor V Leiden, which increases the risk of thrombosis. In fact, 20%–30% of people who have DVT without an identified cause turn out to be positive for the factor V Leiden mutation.
"We've seen many, many patients who have [a factor V Leiden mutation] as an inherited risk factor, and then you add on a second risk factor like surgery or like an estrogen-containing hormone, and that is enough to trigger a blood clot," Dr. Blinder said.
The American College of Chest Physicians' evidence-based guidelines for preventing venous thromboembolism stratify patients undergoing general surgery as low, moderate, high, or highest risk, according to their age, the type of operation, and underlying risk factors (Chest 2004;126:338S-400S).
The guidelines advise early and frequent mobilization for low-risk patients and low-dose unfractionated heparin (LDUH) or low-molecular weight heparin (LMWH) for moderate-risk patients. High-risk patients generally should receive LDUH every 8 hours, or a LMWH such as enoxaparin (Lovenox).
Patients at highest risk for DVT need a full dose of a LMWH such as enoxaparin or the factor Xa inhibitor fondaparinux (Arixtra) in combination with intermittent pneumatic compression (IPC) or graduated compression stockings, said Dr. Blinder, who is on the speakers bureau for GlaxoSmithKline Inc., which manufactures fondaparinux.
Other guidelines that have been issued by the American Society of Plastic Surgeons largely follow these recommendations but instead divide surgical patients into low-, moderate-, and high-risk groups (Plast. Reconstr. Surg. 2002;110:1337–42).
Dr. Blinder suggested that IPC devices may see rising use because newer, fanny pack-size devices are much smaller than previous ones that had to sit at the side of a bed. Graduated compression stockings are thought to increase blood circulation by restricting the venous diameter. IPC devices also restrict venous diameter and are known to more than double the velocity of blood and increase fibrinolytic activity.
A meta-analysis of 15 randomized, controlled trials using IPC to prevent DVT in surgical patients found that the devices could drop the risk of DVT by 60%, compared with no prophylaxis (Thromb. Haemost. 2005;94:1181–5).
Investigators have not resolved the appropriate time to start or stop prophylaxis, but some type of pharmacologic prophylaxis should be included along with mechanical methods, he advised.