Decision Making in Venous Thromboembolism

The first step in treatment is identification of patients who are at high risk of

In standard cases of DVT and PE without hemodynamic compromise, the current standard of care is to initiate parenteral anticoagulation. The immediate goal of therapy is to treat rapidly with anticoagulants to prevent the thrombus from propagating further and to prevent DVT from embolization to the lungs or other vascular beds. The initial treatment of VTE has been extensively discussed and guidelines have been established with recommendations for initiation of anticoagulation; the American College of Chest Physicians (ACCP) released the 9th edition of their guidelines in 2012 based on consensus agreements derived from primary data [51].

Heparin-based drugs are the mainstay of initial treatment. These drugs act by potentiating antithrombin and therefore inactivating thrombin and other coagulation factors such as Xa. Unfractionated heparin (UFH) can be administered as an initial bolus followed by a continuous infusion with dosing being based on weight and titrated to activated partial thromboplastin time (aPTT) or the anti-factor Xa level. Alternatively, patients may be treated with a low molecular weight heparin (LMWH) administered subcutaneously in fixed weight-adjusted doses, which obviates the need for monitoring in most cases [52].LMWHs work in a similar manner to UFH but have more anti-Xa activity in comparison to anti-thrombin activity. LMWH appears to be more effective than UFH for initial treatment of VTE and has been associated with lower risk of major hemorrhage [53].The options for treatment of VTE have expanded in recent years with the approval of fondparinux, a pentasaccharide specifically targeted to inhibit factor Xa. Fondaparinux has been shown to have similar efficacy to LMWH in patients with DVT [54],and while it has not been evaluated directly against LMWH for initial treatment of PE it has been shown to be at least as effective and safe as UFH [55].

Both LMWH and fondaparinux are cleared renally and therefore have increased bleeding risk in patients with renal impairment. In patients with creatinine clearance of less than 30 mL/min, dose reduction or lengthening of dosing interval may be appropriate. Anti-factor Xa activity can be used as a functional assay to monitor and titrate the level of anticoagulation in patients treated with UFH, LMWH, and fondaparinux. Monitoring is useful in the setting of impaired renal function (as above) in addition to extremes of body weight and pregnancy. When used for monitoring of UFH, the anti-factor Xa activity can be measured at any time during administration with a therapeutic goal range of 0.3–0.7 international units (IU)/mL. When used for LMWH, a “peak” anti-factor Xa should be measured approximately 4 hours after dosing, with therapeutic goals depending on preparation and schedule of treatment but generally between 0.6 to 1.0 IU/mL for twice daily and around 1.0 -2.0 IU/mL for once-daily [56].For patients on dialysis, we generally use intravenous UFH for acute treatment of VTE, though recent work has shown that enoxaparin (doses of 0.4 to 1 mg/kg/day) was as safe as UFH with respect to bleeding and was associated with shorter hospital length of stay [57].For long-term treatment of VTE, warfarin is generally preferred based on clinical experience with this agent, though small studies have suggested that parenteral agents may be useful alternatives to warfarin [58].