DEEP VEIN THROMBOSIS
(blood clot)
The chapter is under revision
CONTENTS:
One of the major risks facing patients who undergo total joint surgery in the lower extremities is a complication called deep vein thrombosis (DVT) or blood clot in the veins of the leg.
What is it ?
Thrombosis is formation of blood clots - lumps composed of red blood corpuscles, blood platelets, and fibrin fibers - in the deep veins of the thigh and / or the calf.
The formation of blood cloths in the deep veins of lower extremities can have two serious consequences
- If the clot blocks the blood flow through the vein, blood in the vein beneath the cloth begins to pool. Swelling and pain may develop in the leg; these are the signs of the Deep Vein Thrombosis ( DVT).
- A large clot (thrombus) may break free, travel through the vein system and ultimately plug one of the arteries of the lung. This is a dangerous condition called pulmonary embolus, it can be life-threatening if left untreated.
Picture:
Thrombus of the leg veins and pulmonary embolus
Click on the icon for a full size picture.
Upper picture: Formation of the blood clot - thrombus - in the vein.
The blood clot, a thrombus, is a soft, round, jelly-like formation, which partially or totally fills the vein. It may be only some millimeters small, and it may be several centimeters long.
The blood circulates incessantly through our vessels. The motor that propels the blood through the deep veins of the leg in healthy individuals is the contraction of the leg muscles. The rhythmic contractions of calf and thigh muscles "massage" the blood through the deep veins. Circulating blood is protected against formation of blood clots by sophisticated system of "anti-clot" substances that can mix with the blood only when the blood circulates.
Whenever the muscles are put at rest for longer periods, such as when you are sitting long hours on an airplane or your legs are lying motionless after an operation, the blood flow in the deep veins of the legs ceases.
When the blood in the veins ceases to circulate, the "anti-clot" substances cannot mix with the blood and prevent the formation of blood clots. As a results, the blood platelets begin to accumulate together, the fibrinogen solved in the blood begins to form fast fibers that bind the platelets and red blood cells together in a soft lump, a blood clot is formed.
The thrombus may destroy the delicate valves in the deep veins. These valves have an important function: together with the pumping action of the calf and thigh muscles, these valves direct the blood flow towards the heart. When the thrombus destructs these delicate valves, the blood in the vein stagnates which will result in a painful, chronically swollen leg with distended superficial varicose veins. The name for this late complication of deep vein thrombosis is "postphlebitic syndrome".
Lower picture: The place for formation of the thrombus
The thrombus may form in any vein of both lower limbs, not only in the veins of the operated leg. The forming of blood clots in veins of the limbs is not life threatening in itself.
But if the thrombus grows large and then breaks free it can travel through the veins and eventually reach the lungs. The thrombus can then block the lung vessels, a serious, and potentially fatal condition, called pulmonary embolism.
The dangerousness of a pulmonary embolus depends on its size: small cloths do not even cause any inconvenience to the patients because they obstruct only a small pulmonary vessel. After some time these clots are dissolved and the circulation in the obstructed vein is reestablished. The real incidence of these small lung emboli is thus not known.
A large clot, that obstructs a large lung vessel is, however, dangerous.
The large thrombi that are situated in the thigh veins are the possible source of the pulmonary embolus, whereas the small thrombi in the calf veins, that usually stay there are not dangerous.
Excellent information also on www.dvt.net/html/about.html
How often do the clots occur ?
The majority of DVT do not cause any inconvenience and are not detected. This is demonstrated in the following Table. Only about 5 % of all DVT cause symptoms ("Symptomatic DVT" in the Table). In spite of being silent, large thrombus in the calf or thigh vein may still brake free, travel "upwards" and cause pulmonary embolus.
Type of DVT |
Frequency |
Deep vein thrombosis (DVT) |
40 - 80% |
Symptomatic DVT |
2 -5 % |
Diagnosed pulmonary embolus |
1 - 6% |
Lethal pulmonary embolus |
0,1 - 0,2% |
In the very rare cases the clot is so big that it occludes a large pulmonary artery so that the blood flow to the heart is impaired and death may follow. The incidence of such lethal pulmonary embolus after total hip and total knee operation is about one per thousand total hip or knee operations. (Dahl 1998)
The body can take care of the absolute majority of blood clots everywhere during the 6 weeks period after the surgery. The clots are either dissolved or new veins grow through large clots. (Pitto RP 2002).
There are reports published in renowned journals saying "although the prevailing opinion is that patients with proximal venous thrombosis (blood clots in thigh veins) should be treated with anticoagulants (drugs reducing clotting ability of the blood), our study has shown that all clots regardless of their site and size resolve spontaneously without associated pulmonary embolism"(Kim 2003). This observation has been made on South Korean population. Another study, however, demonstrated that Asian people have a gene that protects them against DVT
There are other reports saying that blood clots cause more deaths than cancers and injuries together (Aventis Pharmaceuticals). These observayions demonstrate that the protection against DVT is indeed a difficult issue.
The signs of DVT
The DVT most commonly occur in just one leg. The symptoms include any or all of the following:
- pain in the calf or in the thigh
- swelling of the lover leg and foot
- the calf and thigh muscles above the clotted veins are painful for palpation
- passive stretching of the calf muscles by pushing the foot cranially ( towards head) provokes severe pain in calf muscles
- discoloration or redness of the calf or thigh area
If you observe any of these signs notice your doctor who decides on further tests and treatment.
The signs of pulmonary embolus
dizziness
shortness of breath
coughing
chest pain.
If you observe some or all of these symptoms notice immediately your doctor because this complication must be treated immediately.
The majority of the thrombi are formed during the operation, but the risk period for development of deep vein thrombosis and pulmonary embolus after total hip or total knee operation extends up to three months after the operation.
Most deep vein thrombi are detected two to five days after the operation when the patient is still in the hospital.
The second period of increased risk for DVT is 10 to 14 days after the surgery, when most patients have already been discharged from the hospital. About 3% of all patients with total hip operations have been readmitted to the hospital during this period because they developed more extensive thrombi in their lower extremities.
Diagnosis
The surgeon uses usually one of the two following methods
- Venography. The radiologist injects contrast material into a vein on the top of the foot. The blood clot appears as a defect in contrast material on the X-ray picture of the veins.
The venography is reasonably accurate, but it is also a costly and painful procedure. Moreover, the irritation of the vein by the contrast material may in itself contribute to the formation of new thrombi.
- Duplex ultrasonography is a method which works with sound waves. The clogged veins are easily distinguished on color pictures produced by this method. This method is painless, no foreign material is injected, and no radiation is required. The method is also cheaper than venography, but it is less sensitive to detect thrombi in lesser veins of the calf.
There are other methods that may confirm the formation of a large thrombus in thigh veins, such as Magnetic Resonance Imaging and plethysmography. Both methods, however, cannot detect the thrombi in calf veins and are used only is specialized cases.
Risk factors
The total hip or knee joint operation itself is the most important risk factor for the development of DVT. There are four different mechanisms that together are responsible for the formation of the thrombi during and after surgery:
- One is the prolonged lameness of lower extremity muscles during and after the operation. The anesthesia impairs the function in calf muscles, which is the motor that maintains the blood circulation in the deep veins of the calf. The blood stagnates and has long contact time with the walls of these veins which encourages formation of a thrombus.
- Second, the reaming and cutting of bone during total joint replacement releases substances that encourage clotting (coagulation) of the blood in the blood system.
This is called a blood clotting cascade system. It is a mechanisms that releases different substances that eventually produce a blood clot in the severed vessel. This is a life saving system, that protects the body from bleeding to death when you cut yourself. Individuals with impairment of this system (hemophiliacs) have life threatening bleeding even after small cuts and traumas.
- Damage of the veins occurs often during total hip or knee replacement as the surgeon retracts, folds, twists or otherwise manipulates soft tissues with included veins. Direct damage of the vein walls always leads to the formation of a thrombus.
- During the total joint replacement, especially during insertion of cemented shafts of total hip prosthesis, the surgeon pushes contents of bone marrow into the circulation. This may be seen on special ultrasound pictures. The contents of bone marrow in the circulating blood trigger the blood clotting cascade system.
Other risk factors that contribute to the formation of thrombi include
previous history of deep vein thrombosis (less that 5 yers ago),
heart disease (congestive , grade II or more),
concomitant malignant disease (cancer),
use of estrogens (and p pills),
haevy smoking and morbid obesity.
Prevention
Prevention of deep vein thrombosis is directed at preventing the stagnation of blood in the veins and to diminish the coagulation tendency of the blood.
- The best prevention of formation of blood clots is an early muscle activity. Most patients with total hip or knee replacement can get out of bed already the day after the operation day and attend physical and occupational therapy sessions. Simple leg lifts and active and passive ankle motions also increase blood flow through the leg veins.
- Mechanical prevention is often used in combination with other devices
Studies demonstrate that the mechanical prevention measures have a well-documented preventive effect on the development of blood clots.
The simplest devices are elastic support stockings (TED's) which compress the soft tissues of the legs and diminish the amount of stagnating blood in the veins.
A more advanced device is a compression stocking sleeve. This is a plastic sleeve put around your leg and connected to a machine which rhythmically increases air pressure in the sleeve. This apparatus simulates the contracting force of your calf muscles and increases the blood flow through veins in the leg. But the rhythmical muscle compression produces also substances that prevent clot forming.
- In most hospitals the surgeons also use pharmacological prophylaxis of deep vein thrombosis in all patients. The patients are given "blood-thinning medicines", in reality so called anticoagulants. These medicines decrease the clotting ability of the blood. Because many clots form already during the operation, the preventive medicines must be given under the operation, which may have unwanted consequences. If given in efficient doses, the blood-thinning medicines would increase bleeding during and after the operation. So here comes the question of the risks and benefits of these medicines.
- The question of the utility of pharmacological prophylaxis against DVT is not clearly decided and the appropriate use of pharmacological prophylaxis is still discussed among surgeons.
On the positive side, several studies showed that pharmacological prophylaxis reduces the formation of blood clots in leg veins by 20 to 50%..
On the negative side, blood-thinning medicines may cause serious bleeding in the operation wound if given during surgery, and they may cause serious bleeding both in the operative wound and elsewhere in the body when given continually after the operation.
There are some important facts you should remember:
- If you are on whatever blood-thinning medicine, you may still get a deep vein thrombosis and pulmonary embolism. Thus, be attentive to the signs of DVT and pulmonary embolism and contact your doctor immediately if you observe any.
- You may get DVT up to three months after the operation, when the blood thinners already have been stopped.
- You should also be aware that as long as you are on blood-thinning medicines you may get a sudden bleeding in the operation wound. If you note a sudden pain and increased swelling of the operation area notice immediately your doctor
- As long as you are on blood-thinning medicines you may get serious bleeding in other organs. You must contact your doctor immediately
If you notice blood in the urine ( may be pink or dark),
bleeding from nose and mouth,
pooling of blood under the skin
coughing or vomiting blood
unusual menstrual bleeding
unusual bruising marks on your skin
pain or swelling in any part of your lower limb
- If you have an epidural catheter or spinal anesthesia, you may get bleeding inside spinal canal when on blood thinning medicines. The bleeding may cause nerve damage. The signs are dizziness, numbness, or tingling in the legs. Thus, if you notice such signs notice immediately your doctor. (In most hospitals the blood thinning medicines are started 6 - 8 hours after removal of the catheter in epidural space)
- If you are on blood thinning medicines, notice your doctor if you have had
a serious fall or if you hit your head
if you become pregnant
if you have rashes, fever, severe diarrhea, vomiting, or nausea
confusion or
rapid heart beat
- While on blood thinning medicines, be very careful with all other medicines, especially with pain medicines that contain aspirin or NSAIDs. These medicines are as a rule forbidden when you are on blood thinning medicines.
Ask always your doctor whether you can continue with your other medicines while you are on the blood thinning regime.
The drugs used for prophylaxis of DVT
The most common anticoagulants (drugs to prevent prevent coagulation of blood) are dextran, aspirin, warfarin, and heparin.
The use of these drugs varies among the surgeons, anesthesiologists, hospitals, and countries
- Dextran is a sugar-like substance given intravenously during and up to two weeks after the operation. There are rare cases of allergy against this substance.
- Aspirin is easy to take by mouth, it is a low- cost drug, its effect needs not to be monitored, and it has few bleeding complications. Its prophylactic efficiency is established in several studies. But it is not tolerated by many patients, some patients even developed dangerous allergies against this drug. Its effect is nowadays questionned by many surgeons.
- Warfarin (dicumarin) acts by blocking the formation of clotting factors in the liver. It takes at least two days before warfarin begins to work, and four to five days before it reaches its maximum effectiveness. Therefore, the drug is often started before the surgery. It is easy to take as pills. The response to warfarin is difficult to predict, its application needs close follow-up with repeated laboratory tests. In spite of these precautions the drug may cause profuse and even dangerous bleeding. The effect of this drug is documented, but the side effects are many.
- Heparin is a naturally occurring substance that inhibits the clotting of blood platelets and erythrocytes.
- A substance called Low Molecular Weight (LMW) heparin is being used recently because it has fewer bleeding complications and its effect is more predictable. LMW Heparin still may cause bleeding, and must be administered by subcutaneous injections.
- Pentasaccharide (Fondaparinux TM) is a new, very effective substance that inhibits the factor Xa which is a key component of coagulation. It can, however, induce some increased bleeding
It is very important that you follow closely all prescriptions and ordinations prescribed by your doctor. You should follow not only the number of pills or injections but also the time (morning, evening, e.g.) when you should take them.
It is important to know that some food substances (vegetables,e.g.) may influence the effect of blood thinners. Ask always your doctor
Treatment of an established deep vein thrombosis.
The goal of the treatment is to stop the growth of the clot and to achieve the lysis of the clot that had already formed. A clot in the calf vein is usually treated on outpatient basis.
If the clot is situated in the thigh vein, the patient needs readmission to the hospital for some five days for treatment with the anticoagulant drugs.
References:
Dahl , Acta Orthop Scand, 1998, 339
Dorr LD et al: Multimodal prophylaxis...J Bone Joint Surg -Am, 2007, 89-A, 2648-57
Kim Y-H et al. J Bone Joint Surg-Br 2003; 85-B: 661-5
Murray et al : J Bone Joint Surg-Br 1996-Br; 78-B: 863- 70
Pitto RP J Bone Joint Surg-Am, 2002, 84-A, 39-48
Warwick D: J Bone Joint Surg-Br 2004; 86-B: 788- 92
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