DEEP VEIN THROMBOSIS (DVT) is a clot that forms most commonly within the deep veins of the legs, but it can also occur in the pelvis or arms. DVT has been increasingly in the spotlight for the last 15 years due to three factors: the rising cost of health care, an increase in preventive medicine, and our aging population.
In this article, I'll fill you in on DVT, including what you need to know about taking care of a patient who already has it and how to prevent at-risk patients from developing it.
But first, let's review the pathophysiology of DVT.
The veins of the body consist of the superficial veins that run near the surface of the skin, and the deep veins, such as the great saphenous and popliteal veins, that are located underneath the muscles and run parallel to the arteries (see Lower limb veins ). Smaller veins connect the superficial and deep veins and help move blood from the skin to the deep veins. Blood is then moved back to the heart with the aid of valves in the superficial and deep veins that allow unidirectional flow. Various factors influence blood flow through the legs: Valves in the veins prevent backflow, while walking and muscle movement in the legs aid blood flow back to the heart. Since blood flow is already slowed as it's squeezed from the connecting veins into the deep veins, there's a high risk of clot (thrombus) formation if any further slowing of the flow occurs. Any time blood slows or is stationary, as in standing or sitting for long periods, there's the potential for a thrombus to form.
Let's now take a look at blood flow to better understand thrombus formation.
Anything that alters the strength of the blood vessel wall can slow blood flow and cause DVT. Think of the vascular system as an intertwining water hose. Normally, water flows through the hose without any difficulty but if you kink the hose, you reduce the flow of water. Over time, dirt and other impurities build up within the hose and add to the reduced flow. The same principles apply to the vascular system. So every time you sit down, curl your legs, or cross your arms, you reduce blood flow, which can cause small clots to form. Normally, the body immediately breaks down these clots. However, when stasis of blood (venous stasis), vessel wall injury, and hypercoagulability—the three factors known as Virchow's triad—are present, an abnormal thrombus will most likely form (see A closer look at Virchow's triad ).
How does the thrombus form? Let's take a look at that next.
Mechanical or physiologic damage to the vessel wall leads to platelet activation. Examples of mechanical damage include high velocity trauma in which bones are broken and surgery, especially orthopedic or abdominal surgery. Examples of physiologic damage include hypertension, in which the vessel wall weakens over time, and phlebitis, in which a vein is inflamed. The platelets adhere to one another and clump together, forming a thrombus (see Picturing venous thrombosis ). After a thrombus forms, it flows in the body and is either dissolved over time or grows and becomes large enough to occlude a vessel. If the thrombus occludes a vessel, it's known as an embolus.
After an embolus forms, the blood behind the blockage slows and the veins expand to accommodate an increase in volume. This leads to a general pooling of blood that slows the blood further and causes more clots to form. Ultimately, the drainage of the lymphatic system slows, leading to edema of the affected extremity.
So who's at risk for developing DVT? That's up next.
Patients who are most at risk for DVT are those undergoing major surgery, especially orthopedic surgery. Other at-risk patients include those who smoke or have lung disease, diabetes, blood disorders, and peripheral vascular disease. But remember, any hospitalized patient is at risk for DVT, especially those who'll be immobile for an extended period of time or are of advancing age. If your patient has any one of the three factors in Virchow's triad, there's the potential for DVT.
See Which surgical patients are at risk for DVT? for more information.
How do you know if your patient has DVT? And if he does, is he at risk for more complications? Let's now review signs and symptoms to be alert for and then we'll take a look at potential complications.
DVT may be difficult to recognize immediately because many patients don't exhibit signs and symptoms or their symptoms are nonspecific. Signs and symptoms include:
- edema or swelling of the affected extremity
- redness
- pain or tenderness
- an increase in the temperature of the affected extremity compared with the rest of the body
- cyanosis and mottling of the skin due to stagnant blood flow.
Although Homans' sign (pain with dorsiflexion of the foot) has historically been used to assess DVT, it's not a reliable or valid sign; in fact, the literature suggests that up to 50% of patients with DVT don't have a positive Homans' sign.
The most serious complication of DVT is pulmonary embolism (PE), in which the dislodged thrombus obstructs the pulmonary artery bed (see Picturing pulmonary emboli ). PE can be life-threatening and may require mechanical ventilation. If your patient complains of any of these signs and symptoms, notify the health care provider immediately:
Another complication occurring in 40% to 60% of patients with DVT is postthrombotic syndrome. Caused by a combination of factors, such as back flow of blood related to faulty valves and blockage that remains in the vessel, signs and symptoms of this syndrome include pain, increased swelling, skin ulcers, and hyperpigmentation. How long postthrombotic syndrome persists depends on the patient's ability to form collateral circulation around any remaining embolus. Treatment for this condition is palliative, including anticoagulation therapy and elevating the affected extremity to help decrease swelling and pain.
Let's say you're worried that your overweight patient with diabetes who doesn't want to get out of his bed to ambulate is developing DVT. What do you do? Careful assessment will help detect early signs of a venous disorder of the legs. Assess for:
- limb pain
- a feeling of heaviness
- functional impairment
- ankle engorgement
- edema
- differences in leg circumferences bilaterally from thigh to ankle
- an increase in the surface temperature of the leg, particularly the calf or ankle
- areas of tenderness or superficial thrombosis.
One of the most reliable physical indications of DVT is unilateral edema of the extremity. Measure the extremity and compare your findings with baseline measurements to detect an increase in circumference. Changes should be reported and documented.
Because DVT is often difficult to detect clinically, diagnostic studies may be indicated. If the health care provider suspects DVT, he may order a venous ultrasound of the patient's legs, magnetic resonance imaging (MRI), a venogram, or a D-dimer test.
Duplex venous ultrasonography , which may be performed at the bedside, is one of the simplest diagnostic tests for DVT. Ultrasound imagery can reveal a thrombus in a deep vein; the Doppler ultrasound measures the blood flow velocity in veins and can detect flow abnormalities. Although a duplex study is noninvasive and relatively simple to perform, its accuracy depends on the technician's skill. If the ultrasound is negative for DVT and the health care team still suspects that the patient has DVT, a venogram may be indicated to make a definitive diagnosis.
MRI is another noninvasive study that can be used to detect DVT in the proximal deep veins. Whether to use this test or a venogram depends on the patient's clinical findings; MRI is more useful than venography in patients with suspected DVT of the inferior vena cava or pelvic veins.Although it's being replaced by ultrasound, the venogram is still considered by many health care providers to be the gold standard for diagnosing DVT. During this invasive test, the patient is placed on a fluoroscopic table that's usually tilted 45 degrees, and a contrast medium is injected into a superficial foot vein. A clinician observes the flow of contrast medium by fluoroscopy and takes X-rays; if the contrast medium doesn't fill the veins normally, acute DVT is confirmed. Complications of venography include hypersensitivity reactions to the contrast medium, acute renal failure because of the volume of contrast medium used, and extravasation of the contrast medium (especially in patients with a history of arterial insufficiency because of tissue necrosis and ulceration). The risk of acute renal failure is higher in elderly patients and in patients with diabetes, hyperuricemia, or multiple myeloma.
A D-dimer test is a blood test to measure fibrin degradation fragments generated by fibrinolysis. An elevated D-dimer level indicates a thrombotic process but isn't specific to DVT. This test is useful as an adjunct to noninvasive testing. If the patient has a low clinical probability of DVT and a negative D-dimer test, DVT can be ruled out without an ultrasound.
It turns out your suspicions were correct—your patient has DVT. What's the next step? Let's look at treatment options next.
The treatment goals for DVT are to prevent the thrombus from growing and fragmenting, which increases the risk of PE; to prevent recurring thrombi; and to let the body's own fibrinolytic system work. Anticoagulant therapy, with unfractionated heparin, low-molecular-weight heparin (LMWH), or oral anticoagulants such as warfarin (Coumadin), is the first-line treatment. Thrombolytic therapy or the factor XA inhibitor fondaparinux (Arixtra) may also be used. Depending on the patient's risk factors, anticoagulant therapy may last from 6 months to 1 year if he has idiopathic DVT or indefinitely if he continues to have recurring thrombi. Let's take a closer look.
Unfractionated heparin is administered by intravenous (I.V.) infusion for 5 to 7 days to prevent the growth of a thrombus and the development of new thrombi. An electronic infusion device is used to prevent the inadvertent infusion of large volumes, which can cause hemorrhage. Unfractionated heparin can also be given subcutaneously to prevent the development of DVT. The dosage of unfractionated heparin depends on the patient's activated partial thromboplastin time, international normalized ratio (INR), and platelet count. Heparin is at an effective (therapeutic) level when the patient's partial thromboplastin time is 1.5 times normal. Patients receiving unfractionated heparin for a long period of time (several days to weeks) are at risk for a sudden decrease in platelet count (30%) known as heparin-induced thrombocytopenia (HIT). If HIT develops, heparin must be discontinued.
Associated with fewer bleeding complications and a lower risk of HIT than unfractionated heparin, LMWH , such as enoxaparin (Lovenox), may be used instead to prevent thrombus growth and new thrombi formation. Given in one or two subcutaneous injections per day, doses are adjusted according to the patient's weight and are based on the specific product and facility protocol. LMWH is more expensive than unfractionated heparin, but it can be used safely in pregnant women and patients who take it may be more mobile.
An oral anticoagulant , such as warfarin (a vitamin K antagonist), is typically administered with heparin therapy. Once the therapeutic level is reached, heparin can be discontinued. If the patient requires long-term therapy, warfarin is frequently used. The dosage of warfarin depends on the patient's prothrombin time and INR; the therapeutic level is reached when the patient's prothrombin time is 1.5 to 2 times normal or the INR is 2 to 3. For more information on warfarin, prothrombin time, and INR, see “Going with the flow: Warfarin” from our July/ August 2004 issue and “Is this on the level?” from our July/August 2006 issue.
Thrombolytic therapy dissolves thrombi in 50% of patients. A thrombolytic, such as activase (Alteplase) or reteplase (Retavase), is given within the first 3 days after acute thrombosis. Thrombolytics cause less long-term damage to the venous valves and reduce the incidence of postthrombotic syndrome; however, they have a higher risk of bleeding than heparin. If bleeding can't be stopped, thrombolytic therapy must be discontinued.
Unlike LMWH, which acts on thrombin and factor Xa, fondaparinux only inhibits factor Xa. Because it doesn't affect platelets, fondaparinux doesn't cause HIT. Fondaparinux is given subcutaneously at a fixed dose once a day and is excreted unchanged by the kidneys; therefore, it must be used with caution in patients with renal insufficiency and it's contraindicated in patients with renal failure.
Surgery may be necessary if anticoagulant or thrombolytic therapy is contraindicated, the patient is at high risk for PE, or his venous drainage is so compromised that permanent damage is likely (see When anticoagulant therapy is a no-no ). Thrombectomy, or removal of the thrombus, is the procedure of choice under these circumstances. During this procedure, a catheter is used to deliver a thrombolytic directly into the clot to dissolve it. A vena cava filter may also be placed through the catheter into the groin, just below the junction of the inferior vena cava and the lowest renal veins, to trap large emboli and prevent PE. About the size of a quarter, this filter made of wire mesh catches any clots that break off the DVT and head for the lungs via the inferior vena cava. A vena cava filter for short-term use has recently been introduced, designed to be removed once the increased risk of PE subsides.
So what can you do to help your patient who's receiving anticoagulant therapy? Let's delve into the care of a patient with DVT next.
When caring for a patient with DVT, you must:
But how about steps you can take to prevent your at-risk patients from developing DVT? Let's take a minute to review prevention strategies.
Elastic compression stockings, which exert sustained, evenly distributed pressure over the calves to help increase blood flow in the deep veins, are usually ordered for patients with venous insufficiency to prevent DVT. They may be knee-high, thigh-high, or like pantyhose. The health care provider may order short-stretch elastic wraps instead, which are applied from the toes to the knee in an overlapping spiral pattern using a one- or two-layer system. Intermittent pneumatic compression devices may also be used with elastic compression stockings to prevent DVT. These devices consist of plastic knee- or thigh-high leg sleeves attached to air hoses and an electric controller. The leg sleeves fill with air to apply pressure to the ankle, calf, and thigh.
If your patient is receiving compression therapy, inspect his skin for signs of irritation and his calves for tenderness whenever you remove the stockings or wraps. Report any skin changes or tenderness to the health care provider immediately.
DVT is a serious, but preventable, condition. With diligent care, your patient with DVT will not only recover, but avoid recurrence as well. And with an eye on prevention, your at-risk patients will be less likely to develop DVT. Now that's good news!
Anticoagulant therapy is contraindicated if your patient has:
Want to beef up your practice when it comes to DVT prevention? Check out the American Association of Critical-Care Nurses' Practice Alert for Deep Vein Thrombosis Prevention at http://www.aacn.org/AACN/practiceAlert.nsf/Files/dvt/$file/DVT%20Prevention%2012–2005.pdf .
Teach your patient who has been prescribed an anticoagulant the following:
- Avoid alcohol because it may change your body's response to the anticoagulant.
- Avoid food fads, crash diets, or marked changes in eating habits.
- Avoid injury that can cause bleeding.
- If you experience faintness, dizziness, increased weakness, severe headaches or abdominal pain, reddish or brown urine, red or black stool, any unusual bleeding, nosebleeds, bruises that enlarge, or rash, contact your health care provider immediately.
- Contact your health care provider before having dental work or elective surgery and inform the dentist or surgeon that you're taking an anticoagulant.
- For women, contact your health care provider if you suspect you're pregnant.
- Wear or carry identification indicating the anticoagulant you're taking.
- Keep all appointments for blood tests
