Heart, Stroke, Women's Health | September 15, 2015 | Author: The Super Pharmacist
Blood circulation begins with the pumping action of the heart. The heart ejects blood into vessels called arteries. Arteries carry oxygen and nutrients to all the body organs and tissues. The arteries become smaller and smaller as they reach their destination. When they arrive at the specific body organ such as the muscle tissue in the legs, for example, they are extremely small and are called capillaries. After oxygen and nutrients are extracted from the blood in the capillaries, the capillaries join back together to form small veins and then, larger veins which travel back to the heart.
The deep veins that lie near the center of the leg are surrounded by powerful leg muscles that contract and force deoxygenated blood back to the lungs and heart. One-way valves in these larger veins prevent the back-flow of blood between the leg muscle contractions. Blood is squeezed up the legs against gravity, and the valves prevent it from flowing back to the feet.
When the circulation of the blood slows down due to illness, injury or inactivity, blood can accumulate or "pool," which provides an ideal setting for clot formation. Deep venous thrombosis (DVT) refers to a blood clot embedded in one of the major deep veins of the lower legs, thighs, or pelvis. Only about 10% of all DVT cases involve the upper extremities.
In DVT, a clot blocks blood circulation through these veins, which carry blood from the lower body back to the heart. The blockage can cause acute pain, swelling, or warmth in the affected leg. Blood clots in the veins can also cause localised inflammation (irritation) called thrombophlebitis. The symptoms can mimic an infection or cellulitis. Under certain conditions, the symptoms of pain and swelling in the leg are inexplicably absent.
More severe complications of DVT occur when a blood clot becomes fragmented and/or dislodges and migrates to a lung artery, causing obstruction of blood flow, leading to severe difficulty in breathing and even death, depending on the degree of blockage. This is called a pulmonary embolus. Compared with DVT, pulmonary embolism is more often fatal, has a higher recurrence rate, and presents with less specific symptoms. Pulmonary embolism is usually a consequence of DVT.
About 40 percent of patients with proximal DVT are found to have an associated pulmonary embolism by lung scan; about 70 percent of patients presenting with pulmonary embolism are found to have DVT in the legs.
'Venous thromboembolism' is the term applied to the occurrence of both deep vein thrombosis (DVT) and pulmonary embolism. It is a common, lethal disorder that affects hospitalised and nonhospitalised patients, recurs frequently, is often overlooked, and results in long-term complications including chronic thromboembolic pulmonary hypertension and the post-thrombotic syndrome. Other than the immediate threat of a pulmonary embolus, the risk of long-term major disability from postthrombotic syndrome is high.
Postthrombotic syndrome is a chronic complication of DVT that manifests months to many years after the initial event. More than 30% of patients who have an acute DVT develop postthrombotic syndrome following the initial episode. Most develop signs and symptoms of this condition within 2 years of the acute event consisting of mild erythema (redness) and localised induration usually exacerbated by standing and relieved by elevation of the extremity. Approximately 5% to 10% will develop severe postthrombotic syndrome with massive extremity swelling and ulceration.11
Over a century ago, Rudolf Virchow described 3 factors that are critically important in the development of venous thrombosis:
These factors have come to be known as the Virchow triad.2 Risk factors include:
Only about half of the people who have DVT have signs and symptoms. These signs and symptoms occur in the leg affected by the deep vein clot. They include:
Some people are not aware of a deep vein clot until they have signs and symptoms of pulmonary embolus. Signs and symptoms of pulmonary embolus include:
As many as 46% with patients with classic symptoms have negative venograms, and as many as 50% of those with image-documented venous thrombosis lack specific symptoms. Thus the clinical examination of DVT is often unreliable; therefore, clinical decision rules (pretest probability scores) based on the patient’s signs, symptoms, and risk factors have been developed to stratify patients into low, moderate, or high clinical probability. Using a clinical decision rule, patients in the low pretest probability category have a 96% negative predictive value for DVT (99% if the d-dimer test is negative as well). This approach helps to improve the effectiveness of diagnosing DVT and to limit the need for additional testing. The American Academy of Family Physicians and the American College of Physicians have developed a joint guideline on the diagnosis and management of venous thromboembolism, and the European Society of Cardiology have developed diagnosis and management guidelines for acute pulmonary embolism.Several pretest probability scoring systems, such as the Hamilton score, the AMUSE (Amsterdam Maastricht Utrecht Study on thromboEmbolism) score, and the Wells clinical prediction rule, are available for DVT assessment. Among them, the Wells rule is perhaps the best known. It divides patients into low-, intermediate-, and high-risk categories. The prevalence of DVT is , and 53 percent for these groups, respectively. The Institute for Clinical Systems Improvement maintains an evidence-based algorithm for the diagnosis of DVT which incorporates the Wells rule, a d-dimer assay, and compression ultrasonography.
A d-dimer test measures a substance in the blood (a fibrin degradation product) that is released when a blood clot dissolves. If the test shows high levels of the substance, a deep vein blood clot may be present. If the test results are normal and the patient has few risk factors, DVT is unlikely.
Compression ultrasound is a variation of the commonly used medical ultrasound technique (which itself is a variation of sonar), in which sound waves are applied to tissue by means of a probe, and an image of the tissue is constructed from the returning sound waves. With compression ultrasound, the ultrasound probe is placed over the suspect vein, and an ultrasound image of the vein is produced, as is typically done with ultrasound techniques. The operator then attempts to compress the vein by pushing on it with the ultrasound probe. Veins are typically highly compressible -- in other words, veins can be collapsed temporarily by applying pressure to them. But if DVT is present, it is relatively difficult to collapse the vein because of the presence of a blood clot, so its compressibility is reduced. When a vein is non-compressible, that is a reliable indicator that DVT is present.
If ultrasound does not provide a clear diagnosis, contrast venography (where a dye is injected into the vein making the vein visible on x-ray) is still the definitive test to rule out the diagnosis of DVT. However, it is not recommended in the initial evaluation because of its invasiveness, technical difficulties, and risks (e.g., hematoma, pain, vessel damage, allergic reaction to contrast media). Venography is reserved for certain scenarios, such as when clinical suspicion is high and noninvasive tests are discordant or equivocal, or when noninvasive tests cannot be performed.
The following guideline20 summarises the current approach for the diagnosis of DVT and venous thromboembolism. The importance of early diagnosis to prevent mortality and morbidity associated with venous thromboembolism cannot be overstressed.
Recommendation 1: Validated clinical prediction rules should be used to estimate pretest probability of venous thromboembolism (both DVT and pulmonary embolism), and for the basis of interpretation of subsequent tests. The Wells prediction rule for DVT and for pulmonary embolism have been validated and are frequently used to estimate the probability of venous thromboembolism before performing more definitive testing on patients. The Wells prediction rule performs better in younger patients without comorbidities or a history of venous thromboembolism than it does in other patients. Physicians should use their clinical judgment in cases where a patient is older or presents with comorbidities. Thromboses in the deep veins proximal to the knee are associated with an increased risk for pulmonary embolism. Those that involve only the calf veins are not associated with an increased risk for pulmonary embolism, but are associated with development of postthrombotic syndrome.
Recommendation 2: In appropriately selected patients with low pretest probability of DVT, obtaining a high-sensitivity d-dimer test is the most reasonable option, and if negative, indicates a low likelihood of venous thromboembolism. However, the d-dimer assay is useful only for ruling out venous thromboembolism if results are negative; positive results are not diagnostic because many conditions, such as impaired renal function, ongoing blood loss, pregnancy, and atrial fibrillation, can cause d-dimer levels to rise. A negative d-dimer assay result combined with a low pretest probability determined by a well-validated clinical prediction rule suffices to rule out venous thromboembolism; no further workup is necessary in such cases, even in patients who have had a prior venous thromboembolism.
Recommendation 3: In patients with intermediate to high pretest probability of DVT in the lower extremities, compression ultrasonography should be the initial test. Ultrasound is less sensitive in patients who have DVT limited to the calf; therefore, a negative ultrasound does not rule out DVT in these patients. Repeat ultrasound or venography may be required for patients who have suspected calf-vein DVT and a negative ultrasound and for patients who have suspected proximal DVT and an ultrasound that is technically inadequate or equivocal.
Recommendation 4: Patients with intermediate or high pretest probability of pulmonary embolism require diagnostic imaging studies. For patients who have intermediate or high pretest probability of pulmonary embolism, imaging is essential. Possible tests include a lung ventilation–perfusion (V/Q) scan (which shows how well oxygen and blood are flowing to all areas of the lungs), multidetector helical computer axial tomography (CT), and pulmonary angiography.
Blood thinners (anticoagulants) are the main treatment for DVT and venous thromboembolism. Several options are available
Fractionated heparin must be given through a small tube placed into a vein (intravenous catheter) and requires blood tests and dosage adjustments at least daily.
Warfarin is an anticoagulant that comes in pill form, but it requires testing and dose changes every few days to weeks.
Low-molecular-weight heparins (LMWHs) are given by injection under the skin and do not require testing and dosage adjustments. These same drugs also treat pulmonary embolism.
Compression or support stockings may help prevent chronic leg pain and swelling (postthrombotic syndrome) after DVT.
According to the American College of Physicians and the American Academy of Family Physicians guidelines,31 low-molecular-weight heparins for DVT result in better outcomes and fewer bleeding complications than unfractionated heparin.
For pulmonary embolism, low-molecular-weight heparin is at least as good as unfractionated heparin. Using low-molecular-weight heparin in patients' homes saves money and is at least as safe as hospital treatment for patients with appropriate support at home. According to one randomised controlled trial, post-thrombotic sequelae were observed in almost half of patients with proximal DVT. Below-knee compression elastic stockings reduced this rate by approximately 50%. Although pregnancy is an important risk factor for DVT, careful comparisons of different treatments in pregnant women are unavailable. For the first episode of DVT, patients should be treated for 3-6 months. Recurrent episodes should be treated for at least 1 year. For a first episode of venous thromboembolism, 3- to 6-month treatment is sufficient. Studies suggest that treatment after 2 or more episodes of venous thromboembolism should continue for at least 12 months, perhaps longer.
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