Deep vein thrombosis (DVT) is the formation or presence of a thrombus in the deep veins. DVT occurs mostly in the lower extremities and to a lesser extent in the upper extremities. Pulmonary embolism (PE) is an obstruction of the pulmonary artery or its branches by a thrombus (sometimes due to fat or air). The most likely source of thrombus in pulmonary arteries is an embolization from deep veins of the legs. This occurs in one-third of patients with DVT. Prevention of DVT thereby decreases the incidence of PE, a serious and life-threatening condition.

Venous thromboembolism (VTE) includes DVT and PE. DVT is a major preventable cause of mortality and morbidity worldwide. DVT and PE account for 60,000 to 100,000 deaths annually in the United States.[1]

Normally, there is a balance of procoagulant and anticoagulant factors in the blood that prevents thrombus formation intravascularly. One or more factors of the triad of Virchow can lead to the formation of DVT.

Triad of Virchow

1. Venous stasis (for example, immobility and congestive heart failure [CHF])
2. Endothelial injury (for example, surgery and trauma)
3. Hypercoagulability (for example,  OCP, cancer, thrombophilia) 

Venous stasis is the most the important factor, but the presence of endothelial injury and/or hypercoagulability increases the risk of DVT. Hospitalized patients are at risk of venous stasis and with the presence of other factors, they are at increased risk of DVT when compared to patients in the community.

DVT prophylaxis methods target either venous stasis (mechanical methods) or hypercoagulability (pharmacological prophylaxis).

Hospitalized patients are at increased risk of developing DVT (approximately 50%), and this increases the risk of PE. PE is one of the most common, but preventable, causes of death in hospitalized patients.[2]

Only 50% of the hospitalized patients receive DVT prophylaxis. Prevention of DVT in hospitalized patients decreases the risk of DVT and PE, which in turn decreases mortality and morbidity.

DVT prophylaxis can be primary or secondary. Primary prophylaxis is the preferred method with the use of medications and mechanical methods to prevent DVT. Secondary prophylaxis is a less commonly used method that includes early detection with screening methods and the treatment of subclinical DVT.

Deep Veins of Lower Extremities

• Common femoral vein
• Deep femoral vein
• Superficial femoral vein
• Popliteal vein
• Anterior tibial vein
• Posterior tibial vein
• Peroneal vein 

Deep Veins of Upper Extremities

• Paired radial vein
• Paired ulnar vein
• Interosseous vein
• Brachial vein
• Axillary vein
• Subclavian vein 

DVT Prophylaxis in Medical Patients

Hospitalized patients are at increased risk of VTE when compared to patients in the community. It is very important to consider DVT prophylaxis in every hospitalized patient. Full history and physical examination are warranted to assess the risk of VTE and bleeding.

Patients with Increased Thrombosis Risk[2]

• Elderly (older than 70)
• Immobile patients
• History of DVT/PE
• Critical ill patients admitted to intensive care unit (ICU)
• Stroke with lower extremity paralysis
• Advanced congestive heart failure (CHF)
• Active cancer 
• Acute respiratory failure
• Thrombophilia
• Recent surgery or trauma
• Obesity
• Ongoing hormonal therapy

Based on thrombosis risk, patients classified into low risk, moderate risk, and high risk for VTE. 

1. Low-risk patients: Young patients with no risk factors for VTE. No need for prophylaxis
2. Moderate-risk patients: With at least 1 risk factors, pharmacological prophylaxis preferred with or without mechanical prophylaxis
3. High-risk patients: With multiple risk factors, pharmacological prophylaxis preferred with mechanical prophylaxis

Commonly used pharmacological agents for prophylaxis in medical patients are:

1.  Low-molecular-weight heparins (LMWH)
2.  Unfractionated heparin (UFH)
3.  Fondaparinux

LMWH is preferred to UFH due to ease of administration (once daily versus 2 to 3 times per day) and decreased incidence of DVT.[3] 

UFH is used in patients with low GFR.

Mechanical methods are used in patients with moderate to high risk for DVT with a high risk of bleeding.

Patients with active cancer but no additional thrombosis risk factors does not need DVT prophylaxis in the out-patient settings. If they have additional risk factors (do not have a chronic indwelling central venous catheter), then either LMWH or UFH are used.

Long-distance travelers with risk factors for VTE can use properly fitted below-knee graduated compressive devices at 15 to 30 mm Hg of pressure along with frequent ambulation and calf muscle exercises. Pharmacological prophylaxis not recommended.

DVT Prophylaxis in Patients Undergoing Orthopedic Surgeries

Risk of VTE (DVT and PE) is high in patients undergoing major orthopedic surgeries like a knee or hip surgeries.

In patients undergoing total hip arthroplasty and total knee arthroplasty, LMWH, apixaban, and rivaroxaban are used. Fondaparinux, UFH, and warfarin are used if above agents cannot be used or contraindicated.

In patients undergoing hip fracture surgery, LMWH, UFH, and fondaparinux are used for DVT prophylaxis.

Duration

At least 10 to 14 days, preferably 35 days from the day of surgery (especially pts undergoing total hip arthroplasty) in the absence of risk factors for bleeding

LMWH typically started 12 hours before and/or 12 hours after surgery. Rest of the medications are typically started 12 hours postoperatively.

Aspirin alone is not generally recommended for DVT prophylaxis. Aspirin is efficacious when compared to placebo in preventing DVT, but there are no comparison studies done with either UFH or LMWH.[4] Aspirin can be used in hybrid therapy, where other agents are used initially while in the hospital and switched to aspirin at discharge.

Patients with a high risk of bleeding are placed on mechanical prophylaxis unless contraindicated.

Patients undergoing an arthroscopic procedure without a prior history of DVT/PE rarely need DVT prophylaxis.

Patients undergoing isolated lower extremity orthopedic surgery requiring immobilization do not require DVT prophylaxis as long as they can ambulate early and adequately.

DVT Prophylaxis in Patients Undergoing Non-Orthopedic Surgeries

VTE risk is based on the type of surgery and underlying patient's risk factors. Major surgeries are categorized as moderate to high risk for VTE and need DVT prophylaxis. When in doubt about the risk of VTE, modified Caprini risk assessment score can be used. This tool scores risk factors from 1 to 5. Based on this assessment score, a patient undergoing surgery can be categorized as below.

Very low-risk patients: No DVT prophylaxis needed

Low risk: Mechanical methods preferred

Moderate to high-risk patients: Pharmacological agents used with or without mechanical methods

LMWH is preferred but UFH used in patients with renal insufficiency. Fondaparinux is used in patients with heparin-induced thrombocytopenia. Other agents are typically not used for DVT prophylaxis.

Duration of DVT prophylaxis is typically for a few days or until patients can ambulate or discharge from the hospital. Prolonged duration of prophylaxis even after discharge from the hospital is not typically recommended.

In patients undergoing abdominal or pelvic surgery for cancer and with a low risk of bleeding, pharmacological prophylaxis is extended to a total of 4 weeks.

Pharmacological Agents

• Low-molecular-weight heparin: Enoxaparin, 40 mg subcutaneously once daily or dalteparin, 5000 units subcutaneously once daily
• Unfractionated heparin: 5000 units subcutaneously every 8 to 12 hours
• Fondaparinux: 2.5 mg subcutaneously daily
• Direct oral anticoagulants: Betrixaban or rivaroxaban
• Warfarin

Mechanical Agents

• Intermittent pneumatic compressions (IPC),
• Graduated compression stockings (GCS) and
• Venous foot pump.

Contraindications for pharmacological DVT prophylaxis include:

• Active bleeding or recent bleeding or high risk for bleeding (active PUD)
• Patients with coagulopathy (INR greater than 1.5)
• Planned surgical procedure in the next 6 to 12 hours
• Thrombocytopenia (Less than 50,000 sometimes less than 100,000).
• Bleeding disorders

 Contraindications for mechanical prophylaxis include:

• Limb ischemia due to peripheral vascular disease
• Skin breakdown