Basic principles of viscoelastic testing

Abstract

BackgroundViscoelastic testing is a method of hemostatic analysis that provides a real‐time, holistic view of ex vivo clotting. It allows for examination of both cellular and plasma protein contributions to clotting including platelet number and function, fibrin(ogen) function, and coagulation factor function. The method assesses physical clot properties during the transition of blood from a liquid to a gel state, either by measurement of clot shear modulus using physical force transduction or by measurement of clot resonance frequency using sonometric interrogation. Results are reported in a live trace, with different trace parameters reflecting different contributors to hemostasis. These reported parameters vary between testing platforms.ResultsIn the United States, there are several commonly used Food and Drug Administration (FDA)‐approved viscoelastic instruments available on the market. Those instruments that use sonometric clot assessment are more recently available and allow for improved portability for use near the patient's bedside. These instruments generally feature different reagent kits that allow more specific interrogation of different hemostatic pathways.Viscoelastic testing can predict the results of traditional plasma‐based coagulation assays and has the added benefit of detecting hypercoagulability and severe hyperfibrinolysis. Implementation of viscoelastic testing in many clinical settings is becoming widespread and has proven to be efficacious in reducing blood transfusion rates in many settings. An impact on overall mortality and morbidity has not yet been demonstrated.ConclusionThis article provides a narrative review of the basic principles of viscoelastic testing, including the science and technology behind the method, as well as currently available testing platforms and reagents.

Same Same but Different: Viscoelastic Hemostatic Assays in Cardiac Surgery

“…Increasing clot stiffness during transition from liquid to gel phase is directly assessed by reduced movement of the oscillating pin or cup. 3,11 Changes over time are reported as multiple parameters and are displayed as a live track.…”

“…With this technique, a focused ultrasound pulse is transmitted into the blood sample creating a shear wave, which causes the blood sample to resonate. 10,11,17 The frequency of harmonic resonance is directly related to the shear modulus and, therefore, allows for detection of clot formation and changes in clot composition. 10,11,17 Different parameters reflect different contributors to hemostasis, and dynamic changes over time are used to form a signature curve.…”

“…MA) and rotational thromboelastometry (ROTEM ® ; TEM Systems Inc, Research Triangle Park, NC) are most commonly used, but novel VHA are emerging in clinical practice. 10,11 In this issue of the Journal of Cardiothoracic and Vascular Anesthesia, DeAnda and colleagues studied 28 patients undergoing elective on-pump cardiac surgery. 12 Results from the Quantra ® Q-plus ® system (HemoSonics LCC, Charlottesville, VA)…”

The quantra hemostasis analyzer compared to thromboelastography (TEG) in the surgical oncologic population: A prospective observational trial

“…Viscoelastic tests, when used as point of care devices, provide real‐time information about the rate of clot formation, clot stiffness, and the rate of clot dissolution 9 . Some studies suggest the use of viscoelastic testing in massively bleeding patients may be associated with improved survival 10,11 .…”

Thrombosis: Grand Challenges Ahead!

“…A third example of where laboratory guided therapeutic management could become relevant is in the use of integral laboratory assays like thrombin generation ( 38 ), viscoelastic assays like Rotem, TEG, or other methods for studying fibrin clot formation and lysis, preferably in a point of care (POC) application ( 39 ). Although viscoelastic assays are increasingly applied in peri-operative and other high risk bleeding settings to guide transfusion management ( 40 ), such assays in conjunction with platelet function assays may help to guide prohemostatic dosing [e.g., the use of antidotes in patients bleeding on oral anticoagulants ( 41 )] but also to optimize anticoagulant therapy.…”