Thromboelastography

Excerpt

Maintaining blood in a liquid state is essential for homeostasis, as it ensures the delivery of sufficient oxygen and nutrients to tissues while removing carbon dioxide and other waste products. Conversely, the ability of blood to convert from a liquid to a solid state—that is coagulate—underlies the mechanism that protects the body from life-threatening exsanguination. This process of thrombosis is normally a localized event at the site of vascular injury while the remaining circulating blood remains in a liquid state. Thrombosis is a dynamic process that includes associated thrombolysis to maintain or restore blood flow through vessels once an injury has been sealed. These unique properties of blood are largely determined by a complex and active balance between pro-coagulation factors, anticoagulants, and fibrinolysis. Two major pathological conditions are commonly associated with the disequilibrium of this intricate system—bleeding and vessel thrombosis.

Major bleeding is a serious medical complication that may be caused by external trauma, surgery, invasive procedures, or an underlying medical condition such as aneurysm rupture or peptic ulcer disease. According to the World Health Organization, injuries are responsible for 5.8 million deaths per year worldwide, with the associated bleeding responsible for about 30% to 40% of these deaths. Several congenital disorders, such as Von Willebrand disease and hemophilia A or B, associated with coagulation factor deficiencies may cause significant bleeding even from minor injuries. In addition, prescribed anticoagulants and antiplatelet agents can induce a coagulopathic state, potentially leading to excessive bleeding associated with trauma or medical procedures. Acute blood loss can lead to coagulopathy due to the depletion of coagulation factors. Predictably, trauma-related coagulopathy has been associated with significantly higher mortality. Patients with ongoing or expected major bleeding benefit from an accurate assessment of the functional state of the hemostatic system to provide optimal care, providing cost-effective replacement of only the necessary blood components.

Venous thromboembolism is another common and serious condition associated with abnormal blood coagulation. In these cases, systemic hypercoagulability shifts the body's homeostatic mechanisms toward a prothrombotic state. However, in many cases, a definitive cause for venous thromboembolism may be unclear. Routine coagulation testing has not been shown to predict such events, and even a detailed hypercoagulability investigation fails to identify an underlying disorder. Many individuals take anticoagulants and antiplatelet agents regularly, which impacts the accuracy of the results of many laboratory coagulation studies. An accurate and cost-effective method to monitor antithrombotic activity could help maintain an acceptable risk-benefit ratio in such patients. Inadequate anticoagulation or antiplatelet therapy can lead to devastating thromboembolic conditions.

Several commonly used blood tests assess blood coagulation. These tests include prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (aPTT), platelet count, fibrinogen concentration, D-dimer levels, activated clotting time, and whole blood bleeding time. These tests are typically used to diagnose coagulopathy and a possible prothrombotic state, monitor anticoagulation therapy, and assist in treating bleeding episodes. More specific factor analyses, such as Factor V, proteins C and S, anti-thrombin III, anticardiolipin antibodies, and prothrombin gene mutation, are useful but not as readily available in emergency clinical situations. Despite their effectiveness for specific clinical applications, such as anticoagulation monitoring, traditional diagnostic tests have notable limitations. One of the primary drawbacks in the context of acute major bleeding is their prolonged turnaround time. Moreover, these tests fail to provide a comprehensive assessment of hemostasis, as they do not evaluate certain factors, such as Factor XIII; platelet function; or fibrinolytic activity. Platelet concentration, easily measured as part of a complete blood count, does not necessarily reflect their function, especially in the presence of elements known to affect platelet reactivity, such as nonsteroidal anti-inflammatory drugs, antiplatelet agents, uremia, malignancy, or alcohol intake. Bleeding time has a low sensitivity and high inconsistency in detecting platelet disorders. Delayed or inadequate diagnosis of coagulopathy in a bleeding patient may lead to an excessive and improperly balanced transfusion of scarce blood components with increased morbidity, treatment costs, and mortality.

Thromboelastography (TEG) is a promising diagnostic modality that offers several advantages compared to other tests mentioned above. TEG was developed in 1948 by Dr Hellmut Hartert at the University of Heidelberg. The first reported clinical application of the test occurred during the Vietnam War in an attempt to guide transfusions of blood components in injured soldiers. In the 1980s, TEG was found to be beneficial in liver transplant patients, and in the 1990s, it was demonstrated to be useful in cardiac surgery. Since then, TEG has become increasingly used as growing evidence supports its clinical efficacy. A PubMed search using the keywords TEG and thromboelastometry results in approximately 6000 publications, highlighting its expanding role in medical practice.

This article outlines the general principles of TEG, including its methodology, normal values, current evidence, clinical applications, limitations, and future research directions.