Thrombosis prevention or thromboprophylaxis is medical treatment to prevent the development of thrombosis (blood clots inside blood vessels) in those considered at risk for developing thrombosis. Some people are at a higher risk for the formation of blood clots than others, such as those with cancer undergoing a surgical procedure. Prevention measures or interventions are usually begun after surgery as the associated immobility will increase a person's risk.
Blood thinners are used to prevent clots, these blood thinners have different effectiveness and safety profiles. A 2018 systematic review found 20 studies that included 9771 people with cancer. The evidence did not identify any difference between the effects of different blood thinners on death, developing a clot, or bleeding. A 2021 review found that low molecular weight heparin (LMWH) was superior to unfractionated heparin in the initial treatment of venous thromboembolism for people with cancer.
There are medication-based interventions and non-medication-based interventions. The risk of developing blood clots can be lowered by lifestyle modifications, the discontinuation of oral contraceptives, and weight loss. In those at high risk, both interventions are often used. The treatments to prevent the formation of blood clots are balanced against the risk of bleeding.
One of the goals of blood clot prevention is to limit venous stasis as this is a significant risk factor for forming blood clots in the deep veins of the legs. Venous stasis can occur during the long periods of not moving. Thrombosis prevention is also recommended during air travel. Thrombosis prophylaxis is effective in preventing the formation of blood clots, their lodging in the veins, and their developing into thromboemboli that can travel through the circulatory system to cause blockage and subsequent tissue death in other organs. Clarence Crafoord is credited with the first use of thrombosis prophylaxis in the 1930s.
Pathophysiology of blood clot prevention The development of blood clots can be interrupted and prevented by the use of medication, changing risk factors, and other interventions. Some risk factors can be modified. These would be losing weight, increasing exercise, and the cessation of oral contraceptives. Moving during periods of travel is a modifiable behavior. Preventing blood clots includes medications that interrupt the complex clotting cascade and changing the proteins needed for clotting. Antiplatelet drugs also have an effect in preventing the formation of clots.
Medical treatments Thrombosis prophylaxis is not only used for the prevention of deep vein thrombosis but can be initiated for the prevention of the formation of blood clots in other organs and circumstances unrelated to deep vein thrombosis:
cerebral complications abortion ectopic pregnancy molar pregnancy pregnancy childbirth and the puerperium coronary portal vein thrombosis intracranial, nonpyogenic intraspinal, nonpyogenic mesenteric pulmonary
Epidemiology of developing blood clots The risk of developing deep vein thrombosis, or pulmonary embolism is different than the total risk of the formation of blood clots. This is due to the observation that not all blood clots form in the lower legs. Most hospitalized medical patients have at least 1 risk factor for thrombosis that progresses to thromboembolism and this risk persists weeks after discharge. Those who remain undiagnosed and not treated prophylactically have a 26% chance of developing a fatal embolism. Another 26% develop another embolism. Between 5% and 10% of all in-hospital deaths are due to pulmonary embolism (as a consequence of thrombosis). Estimates of the incidence of pulmonary embolism in the US is 0.1% persons/year. Hospital admissions in the US for pulmonary embolism are 200,000 to 300,000 yearly. Thrombosis that develops into DVT will affect 900,000 people and kill up to 100,000 in the US. On average 28,726 hospitalized adults aged 18 and older with a VTE blood clot diagnosis die each year. Risk of thrombosis is related to hospitalization. In 2005 the UK the Parliamentary Health Select Committee determined the annual rate of death due to thrombosis was 25,000 with at least 50% being hospital-acquired.
The type of surgery performed prior to the formation of blood clots influences the risk. Without prophylactic interventions, the calculated incidence of clot formation in the lower leg veins after surgery is: 22% for neurosurgery 26% for abdominal surgery 45% for 60% in orthopedic surgery 14% for gynecologic surgery
As the population of the US ages, the development of blood clots is becoming more common.
General risks and indications for blood clot prevention
Some risk factors for developing blood clots are considered higher than others. One scoring system analyzes the probability of clot formation by assigning a point value system to significant risk factors. The benefit of treating those who are at low risk of developing blood clots may not outweigh the higher risks of significant bleeding.
+Risk factor Notes References Previous episodes of thrombosis also a risk factor for embolism formation Family History of Deep Vein Thrombosis Gender, and race not firmly established increased prevalence in women during childbearing years Smoking modifiable, difficult Diabetes Arteriosclerosis Renal disease"hypercoagulable state" VasoconstrictionMyocardial infarction and other types of heart disease Heart attack, Unstable angina Dysrhythmias Heart failure Slow or turbulent blood flow modifiable with exercise Stroke heparins contraindicated Sedentary lifestyle modifiable with exercise Plaster cast transientDehydration modifiablealso related to athletic activities and sports Acute respiratory failure Dysrhythmias Shock Obesity modifiable Pregnancy and the post-partum period "hypercoagulable state" Varicose veins Surgery length of the surgical procedure type of operationhip or knee surgery related to subsequent state of hypercoagulability Lung disease Traumarelated to immobility Estrogen-based oral contraceptive discontinuation reduces risk related to progestogen and ethinylestradiolHormone replacement therapy discontinuation reduces risk Ovarian hyper-stimulation therapy to treat infertility Compression of a vein or artery by abnormality, tumor, hematoma Pacing wires Local vein damage, incompetent valves Central venous catheters Dialysis catheters Repetitive motion injury Immobility associated with air travel, long travel times, and post-surgical – modifiable risk Spinal cord injury Age Cancers Sepsis Polycythemia heparins contraindicated Genetic deficiencies or autoimmune disorders, Protein C and/or S deficiency congenital; associated with warfarin necrosis, heparins contraindicated Antiphospholipid antibody syndrome altered coagulation; heparins contraindicated Factor V Leiden defect altered coagulation Prothrombin G20210A defect altered coagulation; heparins contraindicated Hyperhomocysteinimia altered coagulation; heparins contraindicated Elevated factors II, VIII, IX, XI altered coagulation; heparins contraindicated Antithrobin III deficiency altered coagulation; heparins contraindicated Falls and hip fracture related to immobility Selective estrogen-receptor modulators Erythropoiesis-stimulating agents Acute medical illness Inflammatory bowel disease Nephrotic syndromeMyeloproliferative disordersParoxysmal nocturnal hemoglobinnuria Thrombophilias heparins contraindicated Post-menopausal hormone replacement therapy discontinuation reduces risk Right heart failure Venous inflammation/phlebitis when a thrombus forms, it is thrombophlebitis Sickle cell diseaseArtificial heart valves
{| class="wikitable" |+ Probability and risk estimation for developing blood clots ! Major risk (=1 point) !! Minor risk (=2 points) |- | Cancer || Family history of deep vein thrombosis |- | Immobility || Hospitalization withinthe past 6 months |- | Calf swelling || superficial vein dilation |- | Recent major surgery || redness of area |- | Edema or swelling of only leg ||Recent traumato leg |- | Tenderness inthe calf and/or thigh ||
+ Scoring of the risks associated with the formation of blood clots Probability determination and scoring
Risk for subsequent blood clots Developing blood clots is more probable after the first episode. Risk assessment and intervention for those with one or more episodes of deep vein thrombosis or blood clots in the veins utilize the Well's test. It has been inconsistently modified by several publishers with the results listed below:
Well's and modified Well's risk scoring
+ Well's and modified Well's scoring Finding points references D-dimer abonormal one month after stopping anticoagulants 2 Age > or = to 50 1male1use of hormone at DVT onset1
Adapted for the emergency department + modified Well's scoring Finding points references Malignancy 1 Age > or = to 50 1cast on lower leg/Paralysis/paresis/1Recent surgery or immobility1tenderness over deep vein1entire leg swollen1difference of 3 cm between legs1pitting edema of the affected leg1Collateral superficial veins1another diagnosis more probable than DVT −2
Scoring: less than 2 points – low risk (3%) 2–6 points moderate risk (17%) > 6 points high risk (75%)
General interventions The Centers for Disease Control and Prevention have issued general guidelines describing the interventions that can be taken to reduce the risk of the formation of blood clots:
Interventions during travel Seat-edge pressure from the seat on an airplane on the popliteal area may contribute to vessel wall damage as well as venous stasis. Coagulation activation may result from an interaction between cabin conditions (such as hypobaric hypoxia) and individual risk factors for the formation of blood clots. Studies of the pathophysiologic mechanisms for the increased risk of venous thromboembolism or VTE after long-distance travel have not produced consistent results, but venous stasis appears to play a major role; other factors specific to air travel may increase coagulation activation, particularly in passengers with individual risk factors for VTE.
Interventions for those hospitalized
Compression devices Mechanical compression devices are used to prevent thrombosis and are beneficial enough to be used by patients at low to moderate risk. The use of fitted intermittent pneumatic compression devices before, during, and after procedures is used in inpatient settings. It consists of an air pump and inflatable auxiliary compartments that sequentially inflate and deflate to provide an external 'pump' that returns venous blood toward the heart. The use of intermittent pneumatic compression is common. These devices are also placed on a surgical patient in the operating room (the intra-surgical period) and remain on the person while recovering from the surgery.
The application of antiembolism stockings can be used to prevent thrombosis. The correct use and properly fitted graded compression stockings can reduce the rate of thrombosis by 50%. Contraindications for the use of antiembolism stockings include the presence of advanced peripheral and obstructive arterial disease, septic phlebitis, heart failure, open wounds, dermatitis and peripheral neuropathy. Differences between the use of thigh-high compression stockings and shorter types to prevent blood clots exist, but remain inconsistent.
Assessment