Stop that clot


  • Health
  • Sunday, 16 Nov 2003

By PAUL YEO

A new study has revealed that deep venous thrombosis (DVT) can no longer be considered a rarity in Asia following major surgery despite popular opinion, and steps should be taken to prevent it from occurring. 

 

HAVE you ever wondered why we stop bleeding after a while from cuts and wounds? After all, blood is liquid, so what stops us from losing all our life’s blood every time the skin is breached? 

Leave it to something called haemostasis. This is a complex series of cellular events involving the blood vessel wall and several components of blood, principally platelets and coagulation factors in a process called the blood clotting cascade. 

The interactions between the various proteins involved are complex. Essentially, these proteins are designed to prevent clotting and dissolve existing clots. As a result, the fine line between normal clotting and abnormal clotting is very thin, and this is associated with various malfunctioning or over-activity of these proteins. 

When the skin is breached, the injured blood vessel as well as the surrounding blood vessels constrict. There is a purpose to this as constriction will reduce the flow of blood to the area. The damaged vessel also activates various proteins and clotting factors.  

The final clot itself is made of the protein fibrin, although other components, for example platelet cells, will be trapped and incorporated into the final clot. Fibrin comes from fibrinogen. Fibrinogen is acted on by thrombin during the clotting process to form fibrin. The fibrin molecules initially form a mesh-like substance that is known as a soft clot. Then, the blood clotting factor XIII (fibrin-stabilising factor), acts on the soft fibrin clot to form the hard clot. Factor XIII is also activated by thrombin. 

In addition to its clot-forming role, fibrin also acts as a factor in platelet aggregation), recruiting platelet cells to the site of clotting. Among other things the platelet aggregation assures that the clotting remains localised at the site. 

Thus, tissue damage sets the blood clotting cascade in motion. However, the complexity of the clotting cascade means that there are many potential components that can malfunction.  

For example, haemophilia is a disorder occurring from excessive loss of blood in response to a wound or wounds. It can result from the failure of clot formation, or more realistically, the slow response of clot formation. At the other extreme is thrombophilia, a disorder resulting from over-aggressive clot formation, that can lead to the dislodging of sizeable pieces of clot (embolism). These can be primary instigators of heart attacks or strokes, to indicate the more severe consequences of overzealous clotting. 

 

Venous thromboembolism events (VTE) 

VTEs are disorders due to a disturbance in the clotting mechanism. These include conditions such as deep venous thrombosis (DVT) and pulmonary embolism (PE). DVT describes a clot that forms in the deep veins, commonly in the lower leg. The clot can partially or completely obstruct circulation in the leg. 

DVT can develop in situations where there is prolonged immobility, or where there is an inherited tendency to clot, or an increase in clotting factors following surgery, pregnancy, illness or injury. These may set off the clotting cascade at the wrong time and place. 

DVT can lead to discolouration, pain and the formation of chronic ulcers in the area involved. But the main worry is the development of PE. This occurs when the blood clot in the leg breaks off and is carried in the circulation to the pulmonary artery, where it gets stuck. The clot has essentially blocked off the pulmonary artery. This can be life threatening. As a matter of fact, one in six patients diagnosed with PE will die within three months despite treatment. Where this is concerned, prevention is definitely better than cure. 

At the 23rd Asean Orthopaedic Association Congress held recently in Kota Kinabalu, consultant orthopaedic surgeon Dr Wang Ching Jen from Taiwan presented a paper to his peers about the need to protect patients from DVT, especially those who face major surgeries.  

DVT is not just an economy-class syndrome for long haul passengers. While PEs are suffered by one out of 375,000 travellers, up to two patients out of 100 suffer a fatal PE following major orthopaedic surgery.

In his paper, he revealed for the first time the results of a study, AIDA (Assessment of the Incidence of Deep vein Thrombosis in Asia Following Major Orthopaedic Surgery) that looked at the incidence of VTE in patients who were not given drugs to protect against VTE after major orthopaedic surgery. 

A total of 407 patients were recruited in 19 orthopaedic centres from seven countries – Malaysia, China, Indonesia, Korea, the Phillipines, Taiwan and Thailand. The patients were assessed by undergoing bilateral ascending venographies (injecting dye into the leg veins to visualise the vessel). Out of the 407 patients, 278 venographies fulfilled the assessability criteria.  

It was found that 43.2% of the patients had DVT. In almost 60% of the cases with confirmed DVT on venography, the patients did not experience any local symptoms. PE was clinically suspected in seven of the cases and objectively confirmed in two patients. 

Dr Wang said that the AIDA study definitively demonstrates that, in Asia, DVT is a common complication of major orthopaedic surgery of the lower limbs in the absence of medications to prevent them. “Contrary to popular opinion, VTE is common in Asia, and not just in Western populations. Further support for this comes from a recently completed study in Kaohsiung, Taiwan,” he said. “In a group of 150 patients undergoing total knee replacements, the prevalence of DVT as assessed by ascending venography was 71% in the control group (no medication), vs 50% in the group receiving low molecular weight heparin (LMWH) to prevent DVT,” he revealed. 

Dr Wang emphasised that DVT is not just an economy-class syndrome, referring to its occurrence on passengers on long-haul flights. “While PEs are suffered by one out of 375,000 travellers, up to two patients out of 100 suffer a fatal PE following major orthopaedic surgery,” he revealed. According to Dr Wang, the AIDA study indicates that a more proactive approach is required in the use of thromboprophylaxis (prevention of clot formation) in post-operative major orthopaedic surgery, as well as all other major surgeries that result in prolonged immobilisation of patients.  

On the balance of probabilities, a patient undergoing orthopaedic surgery should not expect to suffer life-threatening consequences such as PE, which raises issues of medical liability for non-treatment. In addition, the cost of treating PE is excessive when compared to the cost of pre-emptive treatment. 

Traditionally, the most common treatment for thromboprophylaxis is LMWH. However, there is now a new class of drug that can be used – Fondaparinux sodium. This drug is made entirely by chemical synthesis, unlike LMWH, which comes from animal sources.  

Fondaparinux sodium acts by inhibiting the production of factor Xa in the clotting cascade. According to Dr Wang, it has demonstrated significant reduction in the incidence of symptomatic VTE in a clinical study involving 7,344 patients, one of the largest studies of its kind. Prophylaxis using the drug from one to four weeks after hip fracture surgery significantly reduced delayed symptomatic VTEs from 2.7% to 0.3% 

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