![]() ![]() ![]() As the clot begins to form and becomes increasingly elastic, the blood will try to return to its original shape following shear stress. Prior to clotting, the whole blood responds to the shear stress with permanent deformation and no force is exerted on the pin. Shear stress is generated as the blood rotates around the pin. The test involved rotating the cup through 38, pausing, and then rotating back to its original position over 9 A pin was suspended on a wire within the sample (Figure 1). 3 VHAs are concerned with observing the transition of blood from its viscous, unclotted state to its elastic, clotted state through measuring the shear modulus.ĭr Hartert’s original VHA consisted of a cup containing an activated blood sample. The degree to which a material resists shear stress is referred to as the shear modulus. Once clotting begins, blood becomes increasingly elastic, resisting shear stress to return to its original shape following deformation. The blood will not return to its original shape and can be thought of as viscous. 2 Before clotting, whole blood will respond to shear stress with permanent deformation. Viscoelasticity refers to a material’s tendency to behave in both a viscous and elastic manner. We will discuss the advantages VHA offers over traditional coagulation assays and the current evidence supporting its use in guiding resuscitation and blood product transfusion. This tutorial will introduce the concept of viscoelastic haemostasis and how it is used to generate meaningful measures of coagulation. 2 The 2 most used viscoelastic haemostatic assays (VHAs) today are thromboelastography (TEG, Haemonetics Corporation) and rotational thromboelastography (ROTEM, Werfen). 1Ĭurrent POCCT relies on the principles of viscoelastic haemostasis, a technology first described by Dr Helmut Hartert in 1948. As a result, there is increasing interest in the use of POCCT in a variety of clinical settings including trauma, cardiac surgery, obstetrics, liver disease, and burns. POCCT offers several advantages over traditional coagulation assays. Point-of-care coagulation testing (POCCT) provides clinicians with the ability to rapidly evaluate the coagulation status of a patient in real time. The use of viscoelastic assays may reduce blood product transfusion and improve patient outcomes however, high-quality prospective evidence remains lacking.Viscoelastic assays may be used to guide resuscitation in major haemorrhage and in those situations in which coagulopathy is common.Conventional coagulation tests take longer to perform and do not provide a measure of platelet function or fibrinolysis.TEG and ROTEM provide the clinician with a holistic view of the clotting process from clot initiation and formation to a measure of clot stability and fibrinolysis.The 2 most used viscoelastic haemostatic assays are thromboelastography (TEG) and rotational thromboelastography (ROTEM).As blood clots, it becomes increasingly elastic. ![]() Point-of-care coagulation testing relies on the property of viscoelasticity. ![]()
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