Deep Venous Thrombosis: The Causes, Treatments, and Preventions

Definition

Deep Venous thrombosis is defined as the presence of a blood clot in a vein, usually a deep vein. This can occur in any vein but usually occurs in the deep veins of the legs.

Prognosis

Mortality from untreated PE (a consequence of DVT) is said to be 26%. This figure comes from a 1960 trial. This is the only study which compared a placebo controlled trial versus the use of anticoagulants (in the treatment of PE). The results of this study were so convincing that the trial has never been repeated. Repeating the trial would be considered unethical. The mortality rate of 26% in the placebo group is probably an overstatement because in the 1960s the technology of the time may only have detected severe PEs.

Patho Physiology

Blood clots can form in deep veins and superficial veins for a variety of reasons. The causes will be discussed later. Inflammation of a vein is called phlebitis. Phlebitis can affect both deep and superficial veins. Superficial thrombophlebitis does not usually cause any serious problems. Home treatments which consist of rest and warmth are generally sufficient. If superficial thrombosis becomes painful then a visit to the General Practitioner is indicated to rule out more serious problems. However, deep vein thrombosis is a very serious condition and requires urgent medical interventions.

The picture below shows the large veins of the leg which thrombose most frequently. These blood clots are dangerous because they can break loose and travel up the venous network into the heart and then the lungs.

Diagram of leg veins showing major veins which are prone to DVT.

When a blood clot in a deep vein becomes dislodged it will be transported by the flowing blood to the narrowest capillary blood network. The patient may not feel that anything is wrong until the blood clot lodges in an organ and causes occlusion of the area. So the blood clot which has formed in the deep vein of the leg will travel upwards through the inferior vena cava into the right atrium of the heart. Contraction of the right atrium will propel it into the right ventricle. The contracting (pumping action) of the right ventricle will push the blood clot to the pulmonary artery’s circulatory network. It will become lodged here because the capillary network is getting progressively smaller. Large clots of blood often cause instant death.

Causes of Deep Vein Thrombosis

Blood normally flows quickly through all major veins of the body. This action prevents it from clotting. Blood from the veins flows towards the heart. The one way flow of blood is facilitated by the squeezing actions of leg muscles, one way valves, osmotic pressures of plasma proteins in the venous capillary network, and the negative pressure in the thorax. In some patients DVT may occur for no apparent reason. However, the presence of any one or combination of the following factors increases the risk of a patient having a DVT.

1. Age: Patients and individuals who are forty years or older have a higher predisposition to DVT.
2. Height: Taller people are more likely to get DVT than shorter people.
3. Immobility is the number one cause of DVT. Immobility causes blood flow in the veins to become slower than usual. Slow flowing blood is more likely to clot than normal flowing blood. This not unlike a pool of stagnant water which becomes stale and infested with micro-organisms. Moving streams of water seldom become infested with micro organisms.
4. Surgical procedures which last more than 30 minutes are the most common causes of a DVT. The patient’s legs become still when he is under anaesthesia. Blood flow in the leg veins can become very slow. Indeed, most surgeries last more than thirty minutes and hence predispose patients to DVT and many other complications. For a full list of post-operative conditions please read:
5. Prolonged illnesses that reduce mobility always result in increasing the risk of the patient developing DVT.
6. Major injuries increase the probability of clot formation in the legs i.e. DVT.
7. Sitting still for prolonged periods of time increases the risk of DVT. Long journeys in boats trains and planes have been shown to cause DVT. Passengers should keep moving their legs even when travelling by these modes of transport.
8. Damage to the inside lining of the vein increases the risk of a blood clot forming. For example, a DVT may damage the lining of the vein. So, if you have a DVT, then you have a higher than average risk of having another one sometime in the future. Some conditions such as vasculitis (inflammation of the vein wall) and some drugs (for example, some chemotherapy drugs) can damage the vein and increase the risk of having a DVT.
9. Clotting Disorders. Blood conditions which cause blood to clot more easily than normal (thrombophilia) increase the risk of having a thrombus forming in veins of the legs. Some medical conditions can cause the blood to become thicker and clot more easily than usual. Two such examples are nephrotic syndrome and antiphospholipid syndromes.
10. Genetic conditions. Some patients with rare genetic inherited conditions can also be predisposed to form clots more easily than normal. One such example is factor V leiden.
11. Contraceptive pills increase the risk to DVT formation.
12. Hormone replacement therapy (HRT) that contains oestrogen causes the blood to clot slightly more easily. Hence patients who are taking “the pill” or “HRT” have a slightly increased risk of DVT.
13. Cancer patients are often dealing with multiple problems. Their problems may include surgery, less activity, changes in clotting times, obesity or wasting. All of these conditions predispose a patient to DVT.
14. Heart failure results in slower circulation and increases the patient’s risk of developing DVT.
15. Older patients are more likely to have a DVT because they have reduced mobility, and serious illnesses.
16. Pregnancy increases the risk. About 1 in 1000 pregnant patients have a greater probability of having a DVT when compared with non-pregnant patients.
17. Obesity slows a patient down and thereby it increases the risk of having the patient having a DVT.
18. Dehydration. Patients who are travelling and are dehydrated are more likely to develop DVT.

Signs and Symptoms of DVT

Most patients present to the ED or the GP’s clinic with a swollen leg which may be painful. Some will present in the early stages with minimal pain. Others will have delayed seeking help until the affected limb is both swollen and painful. Men are more likely to delay seeking help than women.

The affected leg may feel warmer to touch and look “more Pink” in fair skinned patients. In darker skinned patients the colour changes will be hard to distinguish. As the disease progresses, particularly in the latter stages, the calf or thigh will ache and feel extremely tender to touch. Mobility too will be impaired.

The patient may not be able to walk or may walk with a slight limp. If treatment has been delayed then pain will become disabling as the swelling gets worse.

Positive Homann’s Sign. This test should only be performed by a trained individual. This test can cause the blood clot to dislodge and cause a pulmonary embolus. As stated previously, if the embolus is large death may occur almost instantly.

If the blood clot is very small, it may not cause symptoms. In some cases, pulmonary embolism may be the first sign that the patient has had a DVT.

Diagnosis of DVT

The diagnosis of DVT is based on clinical presentation and laboratory tests. Patients often present with a history of “slowed circulation” due to other diseases or disabilities and will usually have one other complicating factor. Complicating factors may include surgery, blood transfusions, resting in bed, infections and clotting disorders.

In the hospital setting, when an inpatient complains of pain in the calf muscle the doctor should be notified. If the patient’s doctor suspects that the patient has DVT then an ultrasound test will be ordered. This measures blood flow through the veins and helps locate the presence of clot(s) which might be slowing venous return.

Another test that is used frequently is the venogram. A venogram is a more refined test and is often ordered when the ultrasound is not clear. A venogram is a radiograph of the flow of blood through the veins. In this test a radio opaque dye is injected into the vein and an x-ray taken. The x-ray will show the clots below the knee, if any.

D-Dimer: This is another blood test. If it is negative then the patient may not have had a DVT.

Treatment and Management of DVT

Treatment of DVT must begin immediately to reduce the chance of the blood clot enlarging and / or dislodging. A dislodged blood clot will flow and through the venous system and lodge in the lungs. This will interfere with oxygenation of blood in the lungs. The ill-effects felt by the patient will be directly proportional to the size of the blood clot.

Nursing Interventions

Upon receiving the patient the nurse must do the primary survey. The primary survey consists of assessing the patient’s airway, breathing and circulation. Then she should proceed and do the secondary survey. The secondary survey consists of assessing the (a) signs & symptoms (b) Allergies (c) Medications (d) Previous Medical history (e) Last meal (f) Events which surrounding the injury / presentation. Finally, the nurse must do the head to toe assessment.

The Primary survey can be remembered with the mnemonic ABC and the secondary survey can be remembered with the mnemonic SAMPLE.

It is recommended the leg be elevated on a pillow to control pain and reduce swelling. This is best done by placing a pillow under the leg when the patient is on bed rest.

Heating pads may reduce the pain and increase comfort. When the patient is ambulatory he may be advised to take short walks.

Patients must be encouraged to wear TEDS (Thrombo elastic deterrent stockings) which work by increasing the blood flow to the heart and by preventing venous pooling (stasis of blood – causes DVT PE. The patient may need to wear these stockings for two years or more after having a DVT.

Patients and persons travelling on long haul flights can also benefit from the use of these stockings.

Medical Interventions

After a patient has been diagnosed with DVT appropriate treatment must be commenced immediately. Obviously this will depend upon the location, size and co morbidities. This is the treating doctor’s area of responsibility.

Treatment of DVT involves testing the blood for clotting time. The Internationalised Normalised Ratio (INR) is used in most countries. The normal INR is 0.9 to 1.2. The treating doctor may decide what INR is best for the patient and he will state this on the patients records so that the nurse and other physicians will know what to do if the INR is not within the level set for the patient. Based on the patient’s INR the patient may be prescribed anticoagulants. Anticoagulants are blood thinners which are only available on prescription. The patient’s INR is checked frequently and the anticoagulant adjusted to within the therapeutic level. Examples of anticoagulants are heparin and warfarin (Coumadin is the trade name for warfarin).

PT/INR and PTT/APTT Management

In the management of DVT the management of clotting factors is essential.

These abbreviations are short forms for terms which follow. The international norms are given but these may be different for different patients.

1. PT is Prothrombin Time. Normal Range is 10 – 12 seconds.
2. PTT is Partial Prothrombin time. Normal is 25 to 38 seconds.
3. Partial thromboplastin time (PTT) or activated thromboplastin (APTT) measure the activity of the intrinsic and common clotting pathways
4. The normal INR is 0.9-1.2 seconds. The normal INR was developed to standardize the different preparations of thromboplastin, universally.
5. Partial thromboplastin time or activated partial thromboplastin time (PTT/APTT) measures the activity of the intrinsic and common pathways
6. The PT/INR and PTT/APTT tests checks factors XII to I (fibrin). Prothrombin time/ International Normalized Ratio, (PT/INR) measures the extrinsic and the common path-ways.
7. PT/INR check factors VII to I (fibrin)
8. The PT test has been replaced by the more sophisticated test

Facts to Remember

1. INR: 2.0 – 3.0 is the normal therapeutic range which must be maintained with warfarin sodium.
2. INR under 2.0 is associated with minimal bleeding.
3. INR of 3 – 4.5: Is associated with excessive bleeding.
4. INR is checked every 4-6 weeks

It must be noted that all clotting factors are produced in the liver except factor VIII which is produced in the endothelial cells of blood vessels. It is for this reason that we see a prolonged PT/INR and PTT/APTT in patients with cirrhosis of the liver (liver failure). This is said to occur when the clotting factor pool has dropped below 50% of normal.

• Factors II, VII, IX, and X are vitamin K dependent clotting factors. Hence vit. K deficiencies will result in clotting disorders.
• In the absence or deficiency of vitamin K, prolonged PT/INR and PTT/APTT values will be seen
• Bile is needed to help with the absorption of Vitamin K which is a fat soluble. Bile is produced in the liver and stored in the gall bladder.
• Low bile production, inadequate vitamin K intake, and chronic small intestinal disease can all result in chronic vitamin K deficiency and prolonged PT/INR and PTT/APTT values
• When compared with other factors, Factor VII has the shortest half-life

In the Acute stage Heparin will be given through a vein (intravenously) or as an IV push. When an IV push is given the dose is much smaller. When the patient is stable then he can be started on Warfarin. Warfarin usually takes about 72 hours to be effective and can be given as a pill. Complete treatment usually involves taking blood thinners for about 3 months. The aim of treatment is to prevent existing clots from growing and dislodging. As stated earlier, dislodged clots may be fatal.

Patient education is a serious issue for patients who have had DVT. The patient needs to be informed to the consequences of not following through with treatment. Regular blood tests and adjustment of medications are important parts of the treatment and management of DVT. These medications are chemicals which are given to the patient to stop clots from forming “so easily”. These medications are only administered after carefully assessing the “risk to benefit ratio”. The treatment team will take several precautions before prescribing anticoagulants. Pregnant patients should not be prescribed heparin as this medication will harm the baby in the uterus. Warfarin and Heparin are also contraindicated for patients planning on having an operation.

The patient should not eat or drink cranberry products while on warfarin as it interferes with the way in which warfarin and heparin work. While on warfarin, patients should not do activities which are likely to cause bleeding or bruising as these medications promote bleeding and bruising.

Use of Thrombolytic Agents in the treatment of DVT

Thrombolytic agents are also called clot busters, clot-dissolving medications, and fibrinolytic agents.

Thrombolytic agents are medications which can dissolve existing blood clots. The main difference between thrombolytic agents and anticoagulants is the anticoagulants prevent a clot from getting larger but do not break down an existing clot. Thrombolytic agents breakdown existing clots by dissolving them. When a clot is dissolved the affected vein reopens. Thrombolytic agents are used to treat coronary Artery Obstructions (Myocardial Infarction) Strokes (Occlusive Cerebrovascular accidents, Deep Venous Thrombosis and Pulmonary Embolus. The active ingredient of thrombolytic medication is cserine proteases. This enzyme digests the protein component of the thrombus and converts the plasminogen to plasmin which then breaks down the fibrinogen and fibrin to dissolve the clot. Some commonly used thrombolytic agents include reteplase (r-PA also known as Retavase), alteplase (t-PA or Activase), urokinase (Abbokinase), prourokinase, anisoylated purified streptokinase activator complex (APSAC), and streptokinase.

Why are thrombolytic agents used? These medications dissolve the blood clot and restore blood flow to the occluded artery or vein.

Directions on how to use: Always follow the manufacturer’s instructions for mixing, dilution, and administration.Never shake this medication vigorously as the drug may become denatured. This simply means that the drugs chemical nature (chemical makeup) alters and may not be suitable for the purpose for which it is prescribed. Most thrombolytic agents are given intravenously under strict medical and nursing supervision. Most frequently the initial dose is followed by a second dose about thirty minutes later.

Before administration nurses should inspect this medication visually for particles or discoloration. If either is present this medication should be discarded as it is not suitable for administration. Needles should be disposed in the sharps container immediately after use.

Thrombolytic agents should only be used under strict medical supervision and should be stopped if there is any evidence of internal or external bleeding. They are most frequently used by specifically trained ambulance crew during myocardial infarction to aid coronary artery perfusion. Thrombolytic agents are never administered in the home situation because they cause bleeding. More detailed information can be obtained from the treating doctor or pharmacist.

Use of Vena Cava Filter in DVT Management

A vena cava filter is a medical device which looks like an umbrella, without the cloth covering. A picture of the device is shown below. This device is inserted into the saphenous vein to prevent blood clots from travelling into the lungs.

This device is used for patients who cannot be treated with blood thinner and are high risk for developing a DVT and PE. In some instances, some patients who are on blood thinners may still be high risk for DVT. This device may be used for them too.

The vena cava filter is an umbrella-shaped stainless-steel devise that causes minimal reduction in venous return. It was designed by Greenfield and Michna. It can be inserted under local or general anaesthesia through the femoral or jugular vein. This filter stays in place because there are hooks which grasp the wall of the inferior vena cava.

The insertion of a Vena Cava filter is a surgical procedure and most often takes place in the operating theatre. This procedure carries all the risks of an operation. Check here for more details on postoperative complications.

Prevention of Deep Venous Thrombosis

Deep venous thrombosis is a serious condition which can result in death. As stated the mortality of 26 % is probably low. There are many things that travellers, patients and persons at high risk can do to prevent deep vein thrombosis.

It is recommended that travellers wear compression stockings during long journeys. The definition of a long journey is any journey which lasts longer than 8 hours.

Passenger on long flights should walk up and down the aisle hourly, flex and point feet every 20 minutes while sitting.

Passengers on long journeys should drink plenty of water but avoid alcohol and beverages with caffeine. Alcohol and beverages with caffeine are dehydrating.

Hospitals realise that all patients at high risk for DVT because most of the patients are less active than usual and have other complicating factors. Patients who are undergoing surgery are at higher risk than other patients.

DVT Prevention in the Surgical Patient

Prevention of deep venous thrombosis is the most effective approach to the problem of pulmonary embolism. Elevation of the lower extremities to facilitate drainage by gravity of venous return prevents venous pooling. It has been shown to reduce the incidence of DVT. It must be note that elevation of the legs with flexion of the knee causes rapid runoff of venous blood in the veins of the leg to the Inferior vena cava.

Sequential compression of the legs by pneumatic pressurizing devices have been able to reduce DVT. In many hospitals most patients will come back from the operating theatre with foot pumps.

Prophylactic anticoagulation therapy has also helped in reducing DVT. Patients who experienced trauma or orthopaedic disorders, including fractures of the hip have benefitted most from this intervention..

LMWHs (Low-molecular-weight heparins) are refined fragments of commercial-grade heparin which are produced by enzymatic or chemical depolarization. These have been shown to reduce the incidence of DVT.

Early mobilization is essential in preventing DVT and chest infections.

The direct removal of venous thrombi used to be recommended. Currently it is not recommended because of the high incidence of recurrent thrombosis postoperatively.

The usage of sleep inducing medications is discouraged as these medications reduce the movements of legs during sleep. Hence they increase the probability of a patient developing DVT.