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Preventing venous thromboembolism in medical/surgical patients

Bartley, Marilynn Kyritsis RN, CRNP, MSN

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Abstract

Learn to recognize who's at risk for this potentially fatal complication and how to reduce your patient's risks.

VENOUS THROMBOEMBOLISM (VTE)—a term that covers deep vein thrombosis (DVT) and pulmonary embolism (PE)—is a major killer in the United States. Most hospitalized patients have one or more risk factors for VTE. In this article, I'll describe who's at risk for VTE and steps you can take to reduce your patient's risk of developing a potentially fatal embolism. (For more details on DVT and PE, see Trouble in the pipelines.)

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Cumulative risk factors

Risk factors for VTE are cumulative, so assess your patient carefully to determine his risk category. (For examples of risk factors, see Who's at risk for venous thromboembolism?)

Low-risk patients are under age 40, immobilized for less than 30 minutes for minor surgery, and have no other risk factors.

Moderate-risk patients are ages 40 to 60 with no additional risk factors or patients with additional risk factors who are having minor surgery.

High-risk patients are over age 60 or are ages 40 to 60 with additional risk factors.

Highest-risk patients are those with multiple risk factors (such as age over 40, cancer, or previous VTE), patients undergoing hip or knee arthroplasty or hip-fracture surgery, and patients with major traumatic or spinal cord injuries.

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Preventive measures

Now let's look at interventions to prevent VTE in various patient populations, following the recently revised American College of Chest Physicians guidelines on VTE prevention. Note that the guidelines don't recommend aspirin alone as sufficient VTE prevention for any patient.

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Patients at high risk for bleeding

Although less effective than anticoagulant drugs, mechanical methods of VTE prevention are safer for patients at high risk for bleeding. These include graduated compression stockings, intermittent pneumatic compression devices, and the venous foot pump, all of which increase venous outflow or reduce stasis in leg veins. Mechanical methods also can be used as adjuncts to anticoagulant drugs.

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General surgical patients

Patients undergoing minor procedures and low-risk patients undergoing general, vascular, gynecologic, or urologic surgery need only early and persistent mobilization.

Moderate-risk patients should be given low-dose unfractionated heparin (LDUH) or low-molecular-weight heparin (LMWH).

High- and highest-risk patients should be given LDUH or LMWH combined with the use of graduated compression stockings or intermittent pneumatic compression devices. Some high-risk patients, including those who have undergone major cancer surgery, should continue anticoagulation therapy after hospital discharge.

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Orthopedic surgery patients

Patients undergoing major orthopedic surgery, such as total knee replacement, total hip replacement, or hip-fracture surgery, should be given an LMWH, the synthetic antithrombotic agent fondaparinux, or an adjusted-dose vitamin K antagonist. The guidelines recommend against using aspirin, dextran, LDUH, or a mechanical compression device as the sole method of VTE prophylaxis.

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Trauma patients

Patients recovering from major trauma (including spinal cord injury and burns) have the highest risk of developing VTE; without prophylaxis, more than 50% of these patients will develop DVT. For those who survive beyond the first day, PE is the third leading cause of death for patients who don't get prophylaxis.

Several risk factors are specific to trauma patients—spinal cord injury, lower extremity or pelvic fractures, femoral venous line insertion, major venous injury repair, prolonged immobility, need for surgery, and coma.

The guidelines recommend that all trauma patients with at least one additional risk factor for VTE receive prophylaxis. If the patient has no major contraindication to LMWH therapy, the guidelines strongly recommend this intervention. Patients who can't have an LMWH because of bleeding risks should receive mechanical prophylaxis with a compression device.

Duplex ultrasound screening is recommended for patients who are at high risk for VTE and who can't have early or aggressive prophylaxis before or after a surgical procedure because of a contraindication such as intracranial hemorrhage. The guidelines recommend against using inferior vena cava filters as primary prophylaxis in trauma patients. Prophylaxis with LMWH or vitamin K antagonist should be continued during inpatient rehabilitation and after hospital discharge.

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Patients with acute medical conditions

An LDUH or LMWH is recommended for acutely ill patients admitted to the hospital for a medical condition such as heart failure, severe respiratory disease, or sepsis or those who are bedridden with one or more additional risk factors. Patients who can't have anticoagulation therapy should be treated with mechanical prophylaxis.

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If VTE develops

The most common physical finding of DVT is sudden swelling in one leg. Patients may complain of a dull ache in the calf that may worsen with ambulation, or they may say their legs feel heavy or tight. On examination the limb may be swollen, red, or warm and may be painful when touched.

Although calf pain on dorsiflexion of the foot (Homans' sign) is the classic assessment finding for DVT, don't rely heavily on this sign; nearly half of all patients with DVT have no physical symptoms or obvious clinical signs. In some cases, the first manifestation of VTE is a fatal PE.

The gold standard for diagnosing VTE is contrast venography, an imaging technique that shows filling deficits in the vein lumen. Unfortunately, contrast venography is invasive, expensive, and uncomfortable, and it may cause phlebitis. Duplex ultrasound screening is now universally accepted because it's accurate for symptomatic DVT, noninvasive, widely available, and easy to repeat.

Treatment for VTE is essentially the same as prevention: anticoagulation therapy including subcutaneous LMWH, intravenous unfractionated heparin, or subcutaneous unfractionated heparin. Patients who can't take anticoagulants, who have complications from anticoagulation therapy, or who have recurrent thromboembolism despite adequate anticoagulation may need an inferior vena cava filter.

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What a patient needs to know

A patient who's had one VTE is at risk for another and must learn to protect himself. For example, he needs to know how to reduce his risk of developing a DVT during long-distance travel. If he'll be flying for more than 6 hours, he should avoid constrictive clothing around the legs and waist and drink plenty of fluids. Because movement protects against VTE, he should stretch his calf muscles frequently and walk around the cabin periodically. Any long-distance traveler with additional risk factors for VTE also should wear properly fitted, below-the-knee graduated compression stockings that provide 15 to 30 mm Hg of pressure at the ankle or be given a single dose of LMWH before the trip. These recommendations also apply to patients making long-distance car trips.

By knowing when to suspect VTE, which factors put patients at risk, and the recommended prevention strategies, you may be able to help your patient avoid a life-threatening complication.

Marilynn Kyritsis Bartley is a trauma nurse practitioner at Christiana Care Health System in Newark, Del.

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Who's at risk for venous thromboembolism?

The following factors raise a patient's risk:

* advanced age

* surgery

* trauma

* immobility or paresis

* malignancy

* cancer therapy (hormonal, chemotherapy, or radiotherapy)

* previous venous thromboembolism

* pregnancy or recent childbirth

* estrogen-containing oral contraceptives or hormone replacement therapy

* selective estrogen receptor modulators

* acute medical illness

* heart or respiratory failure

* inflammatory bowel disease

* nephrotic syndrome

* myeloproliferative disorders

* obesity

* smoking

* varicose veins

* central venous catheterization

* inherited or acquired thrombophilia

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Trouble in the pipelines

A deep vein thrombosis (DVT) develops when the same clotting cascade that stops external bleeding begins in the deep veins, usually in the legs. Normal hemostasis is an intricate interaction of substances that maintain blood in a fluid, clot-free state. If this balance changes, excessive bleeding or inappropriate clotting occurs.

Three factors, known collectively as Virchow's triad, are the primary mechanisms that cause venous thrombosis.

* Vascular wall injury is the single most influential factor leading to thrombosis. Causes include surgery, trauma, indwelling I.V. catheters, injection of irritating substances, I.V. drug abuse, and previous DVT.

* Blood flow abnormalities such as turbulence and venous stasis, which occurs when normal venous flow is impeded. Potential causes of venous stasis include immobilization, vein obstruction or compression, heart failure, shock, and varicose veins.

* Hypercoagulability can be primary or acquired. Primary causes include sickle-cell disease, inherited coagulopathies, and antithrombin III deficiency. Secondary causes include pregnancy, malignancy, and postoperative state.

A pulmonary embolism (PE) is a thrombus that breaks loose from the vein and travels to the lung, causing potentially fatal blood flow obstruction.

A thrombus that doesn't break away from the vein wall can obstruct venous flow and damage the limb, a condition known as postthrombotic syndrome. This syndrome results in scarred veins, damaged venous valves, and malfunction of the normal muscular pump used to return blood to the heart.

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SELECTED REFERENCES

Crowther M, McCourt K. Venous thromboembolism: A guide to prevention and treatment. The Nurse Practitioner. 30(8):26–43, August 2005.
Geerts WH, et al. Prevention of venous thromboembolism. The seventh ACCP conference on antithrombotic and thrombolytic therapy. Chest. 126(3):338S–400S, September 2004.

© 2005 Lippincott Williams & Wilkins, Inc.

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