Arteries have thin muscles within their walls to be able to withstand the pressure of the heart pumping blood to the far reaches of the body. Veins don't have a significant muscle lining, and there is nothing pumping blood back to the heart except physiology. Blood returns to the heart because the body's large muscles squeeze the veins as they contract in their normal activity of moving the body. The normal activities of moving the body returns the blood back to the heart.
There are two types of veins in the leg; superficial veins and deep veins. Superficial veins lie just below the skin and are easily seen on the surface. Deep veins, as their name implies, are located deep within the muscles of the leg. Blood flows from the superficial veins into the deep venous system through small perforator veins. Superficial and perforator veins have one-way valves within them that allow blood to flow only in the direction of the heart when the veins are squeezed.
A blood clot (thrombus) in the deep venous system of the leg is not dangerous in itself. The situation becomes life-threatening when a piece of the blood clot breaks off (embolus, pleural=emboli), travels downstream through the heart into the pulmonary circulation system, and becomes lodged in the lung. Diagnosis and treatment of a deep venous thrombosis (DVT) is meant to prevent pulmonary embolism.
Clots in the superficial veins do not pose a danger of causing pulmonary emboli because the perforator vein valves act as a sieve to prevent clots from entering the deep venous system. They are usually not at risk of causing pulmonary embolism.
Blood clots in the superficial vein system most often occur due to trauma to the vein which causes a small blood clot to form.
Inflammation of the vein and surrounding skin causes the symptoms of any other type of inflammation including:
Often the affected vein can be palpated (felt) as a firm, thickened cord. There may be inflammation that follows the course of part of the vein.
Although there is inflammation, there is no infection.
Varicosities can predispose to superficial thrombophlebitis. When the valves of the larger veins in the superficial system fail (the greater and lesser saphenous veins), blood can back up and cause the veins to swell and become distorted or tortuous. The valves fail when veins lose their elasticity and stretch. This can be due to age, prolonged standing, obesity, pregnancy, and genetic factors.
Deep Venous Thrombosis
The symptoms of deep vein thrombosis are related to obstruction of blood returning to the heart and causing a backup of blood in the leg.
Classically, they symptoms include:
Not all of these symptoms have to occur; one, all, or none may be present with a deep vein thrombosis. The symptoms may mimic an infection orcellulitis of the leg.
Historically, healthcare providers would try to elicit a couple of clinical findings to make a diagnosis. Dorsiflexion of the foot (pulling the toes towards the nose, or Homans' sign) and Pratt's sign (squeezing the calf to produce pain), have not been found effective in making a diagnosis.
Blood is meant to flow; if it becomes stagnant there is a potential for it to clot. The blood in veins is constantly forming microscopic clots that are routinely broken down by the body.
If the balance of clot formation and resolution is altered, significant clotting can occur.
A thrombus can form if one, or a combination of the following situations is present:
- Prolonged travel and sitting, such as long airplane flights ("economy class syndrome"), car, or train travel.
- Trauma to the lower leg with or without surgery or casting.
- Pregnancy, including 6-8 weeks post partum.
- Hypercoagulability (coagulation of blood faster than usual).
- Medications (for example, birth control pills, estrogen).
- Genetic predisposition.
- Polycythemia (increased number of red blood cells).
- Trauma to the vein.
- Fracture to the leg.
- Bruised leg.
- Complication of an invasive procedure of the vein.
Treatment for superficial blood clots is symptomatic with:
- warm compresses,
- leg compression,
- an anti-inflammatory medications such as ibuprofen.
If the thrombophlebitis occurs near the groin where the superficial and deep systems join together, there is potential that the thrombus could extend into the deep venous system. These patients may require anticoagulation or blood thinning therapy (see below).
Deep venous thromboses
Deep venous thromboses that occur below the knee tend not to embolize (break loose). They may be observed with serial ultrasounds to make certain they are not extending above the knee. At the same time, the cause of the deep vein thrombosis may need to be addressed.
The treatment for deep venous thrombosis above the knee is anticoagulation, unless a contraindication exists. Contraindications include recent major surgery (since anticoagulation would thin all the blood in the body, not just that in the leg, leading to significant bleeding issues), or abnormal reactions when previously exposed to blood thinner medications.
Anticoagulation prevents further growth of the blood clot and prevents it from forming an embolus that can travel to the lung.
Anticoagulation is a two step process. Warfarin (Coumadin) is the drug of choice for anti-coagulation. It is begun immediately, but unfortunately it may take a week or more for the blood to be appropriately thinned. Therefore, low molecular weight heparin [enoxaparin (Lovenox)] is administered at the same time. It thins the blood via a different mechanism and is used as a bridge therapy until the warfarin has reached its therapeutic level. Enoxaparin injections can be given on an outpatient basis.
For those patients who have contraindications to the use of enoxaparin (for example, kidney failure does not allow the drug to be metabolized), intravenous heparin can be used as the first step. This requires admission to the hospital.
The dosage of warfarin is monitored by blood tests measuring the prothrombin time or INR (international normalized ratio). For an uncomplicated deep vein thrombosis, the recommended length of therapy with warfarin is three to six months.
Some patients may have contraindications for warfarin therapy, for example a patient with bleeding in the brain, major trauma, or recent significant surgery. An alternative may be to place a filter in the inferior vena cava (the major vein that collects blood from both legs) to prevent emboli from reaching the heart and lungs. These filters may be effective but also may be the source of new clot formation.
Surgery is a rare option in treating large deep venous thrombosis of the leg in patients who cannot take blood thinners or who have developed recurrent blood clots while on anti-coagulant medications. The surgery is usually accompanied by placing an IVC (inferior vena cava) filter to prevent future clots from embolizing to the lung.
Phlegmasia Cerulea Dolens describes a situation in which a blood clot forms in the iliac vein of the pelvis and the femoral vein of the leg, obstructing almost all blood return and compromising blood supply to the leg. In this case surgery may be considered to remove the clot, but the patient will also require anti-coagulant medications.