OVERVIEW

What is deep vein thrombosis of the lower limbs?

Deep vein thrombosis (DVT) of the lower limbs, also known as lower extremity deep vein thrombosis, is a common condition in daily life.

Based on the types of blood vessels in the human body, thrombosis can be classified into venous thrombosis, arterial thrombosis, and capillary thrombosis. A well-known example, cerebral thrombosis, falls under arterial thrombosis.

Deep vein thrombosis of the lower limbs occurs when blood clots form in the deep veins of the legs, creating blockages that impede blood flow. DVT can be broadly categorized into acute and chronic types.

DVT cannot be completely cured, so early detection and treatment are crucial. Delayed treatment may lead to life-threatening complications such as pulmonary embolism.

SYMPTOMS

Can deep vein thrombosis in the lower limbs travel to other parts of the body with movement?

As is well known, venous blood returns to the heart and then enters the pulmonary circulation for oxygen exchange and carbon dioxide removal. Venous blood from the deep veins of the lower limbs flows through the inferior vena cava → right atrium → right ventricle → pulmonary artery → pulmonary capillary network → pulmonary veins → left atrium → left ventricle → systemic arterial system.

Thus, if a deep vein thrombus in the lower limbs dislodges, it will travel along the relatively large inferior vena cava, right atrium, and right ventricle into the pulmonary artery. The pulmonary artery branches and narrows progressively, so the dislodged thrombus may become lodged at a certain point, causing pulmonary embolism. The capillaries of the pulmonary circulation are very narrow, preventing the thrombus from passing through. Therefore, under normal circumstances, it does not lead to common arterial embolisms such as cerebral or renal embolism.

What are the symptoms of deep vein thrombosis in the lower limbs?

The symptoms of deep vein thrombosis in the lower limbs vary significantly depending on its location. Thrombosis can occur in any deep vein of the lower limbs (e.g., iliac, femoral, popliteal, anterior tibial, posterior tibial, or intermuscular veins).

The most common clinical manifestation is sudden swelling in one limb, accompanied by localized pain that worsens with walking. In milder cases, patients may only experience a sense of heaviness when standing.

What does the pain caused by deep vein thrombosis in the lower limbs feel like?

If thrombosis occurs in small venous plexuses, the affected area is limited, the symptoms are mild, and the pain is not significant.

For example, thrombosis in the deep veins of the calf—though the most common site post-surgery—may sometimes present with subtle or no symptoms, requiring diagnostic measures like the Homans' sign to elicit pain. In individuals with a low pain response, abnormalities may go unnoticed until the thrombus grows and affects major veins, causing venous return obstruction. This leads to calf pain, tenderness, and mild to moderate swelling.

How do symptoms differ based on the location of deep vein thrombosis in the lower limbs?

• Iliac-femoral vein thrombosis: Most cases develop secondary to calf deep vein thrombosis, meaning severe thrombi typically spread upward from the calf to the thigh. Due to the extensive involvement and prolonged duration, the inflammatory response is more pronounced, causing venous return obstruction. In addition to localized pain and tenderness, patients may experience heaviness and aching throughout the limb.

• Limb swelling: If major veins are affected, rapid and severe swelling occurs. Thrombosis in smaller deep veins results in only mild swelling.

• Superficial vein dilation: This occurs due to deep vein obstruction, impairing superficial venous return. The severity depends on the location and extent of the thrombus.

• Systemic reactions may also occur to varying degrees.

What systemic reactions can deep vein thrombosis in the lower limbs cause?

• Fever and increased pulse rate, leading to phlegmasia cerulea dolens:

  • The most severe form of acute deep vein thrombosis occurs when thrombi extend to most or all of the venous system, particularly the deep femoral vein, causing severe venous return obstruction. This is often accompanied by femoral artery spasm, known as phlegmasia cerulea dolens.
  • Sudden onset, with widespread limb pain, swelling, shiny and tight skin, cyanosis, blistering, and temperature changes. The dorsalis pedis and posterior tibial pulses weaken or disappear. Systemic reactions include fever and shock due to rapid fluid leakage into the limb. Late-stage venous gangrene may occur.

• If the condition progresses, intense arterial spasm may lead to phlegmasia alba dolens:

  • This results from rapid and extensive thrombosis, causing severe lower limb swelling within hours. Symptoms include pale skin and a网状扩张 of subcutaneous veins, termed painful phlegmasia alba dolens.
  • Limb necrosis indicates severely compromised circulation.

• The most serious complication is pulmonary embolism, causing intractable dyspnea and potentially life-threatening cardiac effects.

Where are the deep veins located in the lower limbs?

These deep veins are large veins situated beneath the muscles of the lower limbs, distinct from superficial veins.

Deep veins are the primary pathways for venous return, receiving blood from superficial veins.

During catheter-directed thrombolysis, the catheter is inserted into the deep vein (often the popliteal vein behind the knee) to deliver thrombolytic drugs directly to the thrombus.

What diseases can deep vein thrombosis in the lower limbs cause?

First, it’s important to understand complications—a complex clinical concept referring to secondary conditions arising from a primary disease.

• Pulmonary embolism: The most severe complication, occurring when a large thrombus dislodges and blocks the pulmonary artery.

• Inferior vena cava obstruction syndrome: Results from iliac vein thrombosis extending upward.

• Post-thrombotic syndrome: After treatment, symptoms may improve, but standing or activity can cause recurrent swelling. Over time, superficial varicose veins, skin pigmentation, hardening, and chronic ulcers may develop, resembling late-stage chronic venous insufficiency.

CAUSES

What Causes Deep Vein Thrombosis in the Lower Limbs?

There are many causes of deep vein thrombosis (DVT) in the lower limbs, with most cases resulting from three main factors: slow blood flow in the veins, vein wall injury, and hypercoagulability of the blood.

What Causes Slow Blood Flow in Patients with Lower Limb Venous Thrombosis?

• Prolonged immobilization of the lower limbs (lack of movement), such as long-term bed rest due to illness, prolonged sitting or squatting, or severe varicose veins.

• In surgical patients, spinal or general anesthesia can cause peripheral vein dilation, slowing venous return.

• Anesthesia during surgery paralyzes the lower limb muscles, eliminating their contraction function and impairing the muscle pump effect (which helps venous blood return to the heart through muscle movement).

• Postoperative bed rest due to incision pain or other reasons reduces patient mobility, further diminishing the muscle pump effect, slowing blood flow, and increasing the risk of DVT.

What Causes Vein Wall Injury in Deep Vein Thrombosis?

• Chemical Injury: Intravenous injection of irritating or hypertonic solutions, such as antibiotics, organic iodine solutions, or concentrated glucose, can damage the vein lining, leading to phlebitis and thrombosis.

• Mechanical Injury: Local vein bruising, tearing, or trauma from bone fractures (e.g., femoral neck fractures damaging the femoral vein or pelvic fractures injuring the iliac vein) can cause thrombosis.

• Infectious Injury: Septic thrombophlebitis, caused by nearby infections, is relatively rare.

What Causes Hypercoagulability in Deep Vein Thrombosis?

The first category is congenital hypercoagulability, mainly due to deficiencies in thrombotic inhibitors, abnormal fibrinogen, or impaired fibrinolysis.

The second category is acquired hypercoagulability, caused by trauma, shock, surgery, cancer, long-term estrogen use, pregnancy, etc.:

• Major surgeries increase platelet aggregation and reduce fibrinolysis due to elevated inhibitors of plasminogen activators and plasmin. Excessive use of hemostatic drugs can also induce hypercoagulability.

• Splenectomy in general surgery suddenly raises platelet counts, increasing blood coagulability. Severe burns or dehydration can also thicken the blood.

• Another often overlooked cause is advanced cancer (e.g., lung or pancreatic cancer), where tumor cells disrupt tissues, leading to hypercoagulability.

Who Is at Higher Risk for Lower Limb Deep Vein Thrombosis?

Based on the causes mentioned above, individuals with the following risk factors are more prone to DVT:

• Prolonged immobilization, long-term bed rest, extended sitting during travel (e.g., long flights or car rides), or severe varicose veins from prolonged sitting or squatting.

• Long-term IV administration of irritating or hypertonic solutions, or conditions like lower limb fractures, trauma, shock, surgery, cancer, estrogen use, oral contraceptives, or pregnancy.

• Postpartum women are also at higher risk for DVT.

• Anatomical factors, such as compression of the left iliac vein by the right iliac artery, slowing venous return compared to the right side.

• Previous history of DVT, especially when combined with other risk factors, increases recurrence risk.

Is Deep Vein Thrombosis Hereditary?

DVT is not generally considered hereditary, but some underlying causes may have a genetic component.

For example, deficiencies in protein C (a vitamin K-dependent glycoprotein synthesized in the liver) can disrupt coagulation and fibrinolysis, leading to thrombotic disorders like DVT or disseminated intravascular coagulation. Elevated levels of α₂-globulin or α₁-antitrypsin can also increase recurrence risk.

Genetic mutations causing deficiencies or dysfunction in regulatory proteins can lead to primary hypercoagulability, an autosomal dominant disorder characterized by unexplained thrombotic tendencies.

DIAGNOSIS

How is the Homans' sign test performed during physical examination for patients with deep vein thrombosis of the lower extremities?

Also known as the straight-leg dorsiflexion test. During the examination, the patient is instructed to keep the lower limb straight. When the ankle is dorsiflexed, the passive stretching of the gastrocnemius and soleus muscles irritates the affected veins in the calf muscles, causing deep pain in the calf. A positive result suggests deep vein thrombosis in the calf.

How to differentiate limb swelling caused by deep vein thrombosis of the lower extremities from swelling caused by other conditions?

Swelling of the lower limbs caused by deep vein thrombosis often needs to be distinguished from swelling due to congestive heart failure, chronic renal insufficiency, anemia, hypoproteinemia, pelvic malignancies compressing the iliac vein, or inferior vena cava obstruction caused by Budd-Chiari syndrome.

In most cases, these conditions cause bilateral, symmetrical edema, which can be distinguished from deep vein thrombosis by other symptoms of the primary disease:

• For example, heart failure-related edema is not limited to the lower limbs but often systemic, accompanied by orthopnea, pitting edema without tenderness.
• Chronic renal insufficiency may present with morning eyelid edema, ammonia-like breath odor, and often features such as anemia, bleeding tendency, and hypertension.
• Swelling due to anemia or hypoproteinemia is usually milder, progresses more slowly than deep vein thrombosis, lacks tenderness, and shows no significant change in skin temperature.
• Unilateral lower limb symptoms caused by pelvic malignancies or Budd-Chiari syndrome are similar to deep vein thrombosis but can be clearly differentiated by venography or ultrasound.

What tests are needed for diagnosing deep vein thrombosis of the lower extremities?

Initial screening and early diagnosis primarily rely on key clinical symptoms, as mentioned above. Further confirmation and localization of the thrombus require diagnostic imaging.

Main tests include:

• Laboratory tests: Mild elevation of white blood cells and neutrophils.
• Venography: The gold standard for diagnosis, offering the highest accuracy. However, it is invasive and requires contrast agents, so indications must be strictly controlled. Caution is advised for patients allergic to contrast agents or with renal impairment.
• Doppler ultrasound: The most commonly used clinical method, effective for thrombus screening. It detects venous blood flow sounds or waveforms via a surface probe but may miss small or early-stage thrombi.
• Magnetic resonance venography: Rarely used in clinical practice.

Is anesthesia required for venography in patients with lower extremity venous thrombosis?

No. Lower extremity venography for deep vein thrombosis typically uses anterograde contrast injection, following the physiological blood flow to visualize the veins and detect thrombi.

Before the procedure, an iodine allergy test is essential. If no allergy is found, the examination proceeds. The patient lies supine on an X-ray table at a 30-degree head-up tilt. A tourniquet is applied above the ankle to block superficial venous flow. A 9-gauge scalp needle is inserted into the dorsal foot vein, and 40–80 ml of 38%–45.6% meglumine diatrizoate is injected over 5–10 minutes. As the procedure involves only superficial vein puncture, anesthesia is unnecessary, and no significant sequelae occur.

TREATMENT

Which department should be consulted for deep vein thrombosis in the lower limbs?

General Surgery, Vascular Surgery.

How is deep vein thrombosis in the lower limbs treated without surgery?

Bed rest and elevation of the affected limb:

• Elevating the leg and initial bed rest can relieve pain in patients with acute leg swelling due to deep vein thrombosis. Bed rest for 1–2 weeks is recommended to prevent pulmonary embolism.
• After the placement of an inferior vena cava filter, patients can be encouraged to move early, which may lead to faster improvement in pain and swelling.

Anticoagulation therapy:

• This is one of the primary modern treatments for deep vein thrombosis.
• Proper use of anticoagulants can reduce the incidence of pulmonary embolism and complications from deep vein thrombosis. Their role is to prevent the growth of existing clots and the formation of new clots elsewhere, while promoting faster recanalization of thrombosed veins.
• Heparin or low-molecular-weight heparin is typically used in the acute phase, followed by oral anticoagulants such as warfarin.
• Due to warfarin's complex interactions with drugs and food, significant individual dosage variations, and bleeding risks requiring monitoring, many new oral anticoagulants, such as rivaroxaban, have been developed in recent years.

Intravenous thrombolysis:

• Medication is administered through superficial veins in the hand or leg, allowing the drug to distribute evenly in the bloodstream to achieve thrombolysis.
• Commonly used drugs include urokinase.

Interventional thrombolytic therapy:

• Thrombolytic drugs are delivered directly to the site of thrombosis via a catheter for precise treatment.

What should patients with deep vein thrombosis in the lower limbs pay attention to when taking warfarin orally?

Oral warfarin requires regular coagulation function tests, with the primary monitored indicator being the International Normalized Ratio (INR).

• For deep vein thrombosis treatment with warfarin, the drug usually takes 3–4 days to take effect. The INR value measured on the third day should generally be less than 2, ideally around 1.5. If it exceeds 2, the dosage should be reduced.
• After one week, a follow-up test is needed. For young and middle-aged patients, the INR should be maintained between 2–3, while for elderly patients, it should be around 1.6–2.5, indicating effective and safe anticoagulation. Compared to aspirin, adjusted-dose warfarin (INR 2.0–3.0) significantly reduces the incidence of thromboembolic events but requires close monitoring to avoid INR > 3.0.
• The anticoagulation intensity of warfarin (INR) should not be below 1.5. When INR > 3, the risk of bleeding complications increases significantly, while INR < 1.5 raises the risk of embolism.

How soon can patients with deep vein thrombosis in the lower limbs resume normal activities after surgery?

After lower limb venous thrombosis surgery, once the patient's vital signs stabilize, they should be encouraged to move their legs appropriately. Compression stockings or bandages can be used, and early mobilization is recommended to avoid prolonged bed rest and recurrent thrombosis.

Can deep vein thrombosis in the lower limbs be completely cured?

Like most medical conditions, deep vein thrombosis in the lower limbs cannot be completely cured but can be managed to the greatest extent possible.

If thrombolytic therapy is administered within the first 3 hours of the acute phase, newly formed clots can be largely dissolved. However, as the condition progresses, the thrombus contracts and adheres to the venous wall due to inflammation, making complete dissolution unlikely even with thrombolytic drugs.

Surgical thrombectomy may also damage the blood vessel walls, increasing the risk of recurrence. Therefore, early detection and treatment are crucial for better outcomes.

Under what circumstances must patients with deep vein thrombosis in the lower limbs undergo surgery?

The need for surgery depends on the severity of the condition. In the acute phase, systemic or local thrombolytic therapy can be administered.

With the widespread use of interventional therapy, early-stage acute thrombosis treated with interventional thrombolysis has a high cure rate. For late-stage chronic deep vein thrombosis, if the thrombus becomes organized and completely blocks the vessel, surgery is the only option.

Is hospitalization necessary for deep vein thrombosis in the lower limbs?

Due to the high risk of complications and the specialized nature of treatment, deep vein thrombosis in the lower limbs is best managed in a hospital setting.

In the hospital, patients receive comprehensive care under medical supervision, with 24/7 access to emergency treatment. Outside the hospital, there are no professional medical staff or necessary emergency equipment and medications.

What should patients with deep vein thrombosis in the lower limbs pay attention to during hospitalization?

Hospitalization for deep vein thrombosis is primarily for treatment, so most emergencies during this period are treatment-related complications. Below is an overview of common situations, indicating which can be self-managed and which require immediate medical attention.

General conditions:

• Abdominal bloating during hospitalization is usually due to reduced gastrointestinal motility from prolonged bed rest. Drinking more water, eating easily digestible foods and vegetables, and moderate activity can help.
• Dizziness upon standing is often due to postural hypotension and is not usually a cause for alarm. Since patients have been bedridden, sudden movement or standing up quickly can lead to low blood pressure. Advise the patient to move slowly. If fainting occurs, a doctor should be called to rule out other conditions.
• Fever, if not accompanied by other discomfort, may be due to thrombus dissolution and absorption and is generally not a concern.

Special conditions:

• Oral or skin mucosal bleeding, subcutaneous bruising, etc., may indicate excessive anticoagulant or thrombolytic dosage, requiring immediate medical attention.
• Side effects such as rash, fever, or leukopenia may occur due to medication.
• Allergic reactions, fever, or chills may indicate an allergy to thrombolytic drugs, requiring urgent medical treatment.
• Swelling or pain at the vascular puncture site for thrombolysis may indicate hematoma formation and requires immediate intervention.

DIET & LIFESTYLE

What should patients with deep vein thrombosis (DVT) in the lower limbs pay attention to after treatment?

After systematic treatment, the symptoms in the lower limbs can generally be relieved to varying degrees. If thrombolytic therapy is administered within 72 hours of DVT onset, lower limb symptoms may return to their original state, but the course of recovery is prolonged. For patients with severe symptoms, even after comprehensive treatment, old thrombi in the veins may not dissolve completely, and the recurrence rate remains high.

Therefore, in daily life, patients are advised to:

• Engage in moderate lower limb activity. When resting in bed, elevate the affected limb by 10–15 degrees (approximately the height of two pillows) to promote blood circulation.

• Wear medical compression stockings during activity. After treatment, patients may experience symptoms like lower limb swelling due to damaged venous valves or residual organized thrombi narrowing the blood vessels, which affects venous return.

• Most DVT patients require continued oral medication for some time after discharge. It is essential to follow the doctor's instructions strictly.

• In daily life, keep the lower limbs active and avoid prolonged standing, squatting, etc.

What should DVT patients pay attention to in daily life?

• Increased physical activity or abdominal pressure may dislodge thrombi, leading to pulmonary embolism. Therefore, DVT patients should consume high-fiber foods to maintain smooth bowel movements and avoid straining, which could suddenly increase abdominal pressure and cause thrombi to dislodge.

• Maintain a light, easily digestible diet rich in vitamins and fiber, such as fresh vegetables (e.g., tomatoes) and fruits (e.g., pears, apples, black fungus), to ensure regular bowel movements.

• Drink plenty of water to reduce blood viscosity and prevent worsening the condition.

• During hospitalization, opt for liquid or semi-liquid bland diets, avoiding hard, salty, or spicy foods that may irritate oral mucosa. Before sleep, avoid stimulants like coffee or strong tea; instead, drink warm milk or listen to soft music to relax and improve sleep quality.

• In daily life, wear compression stockings and engage in moderate exercise. Minimize prolonged standing, squatting, or sitting, which hinder venous return. Elevate the lower limbs appropriately after activity.

• Patients with chronic cough or habitual constipation should seek timely treatment for these underlying conditions.

PREVENTION

How to Prevent Deep Vein Thrombosis in the Lower Limbs?

• For high-risk patients, comprehensive preventive measures should be taken. For example, surgical patients should receive necessary pharmacological prophylaxis before and after surgery.
• Avoid placing pillows under the calves after surgery, as this may hinder venous return in the lower legs.
• Patients should frequently move their feet and toes actively and perform deep breathing and coughing exercises.
• Get out of bed and move as early as possible, and wear medical compression stockings if necessary.
• Elderly individuals, cancer or heart disease patients undergoing major thoracic, abdominal, or pelvic surgeries, those with femoral fractures, and postpartum women should pay extra attention to prevention. In daily life, they should:
  • Reduce intake of greasy and spicy foods and consume more vitamin-rich foods.
  • Consider taking oral medications to promote blood circulation.
• For the general population, prolonged standing, squatting, or sitting should be minimized to avoid slowing blood flow. Moderate physical exercise is recommended.