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PRECISION NEUROCRITICAL CARE : THROMBOELASTOGRAPHY By Fawaz Al-Mufti, MD & Christopher Zammit, MD The authors have no actual or potential conflict of interest in relation to the topics discussed in this column. This article may discuss non-FDA approved devices and “off-label” uses. The NCS and Currents do not endorse any particular device. Thromboelastography (TEG®) and rotational thromboelastogram (ROTEM®) are commercially available viscoelastic hemostatic assays (VHAs) that provides insight into the global visco-elastic properties of whole blood clot formation under low shear stress. Since VHAs are performed on whole blood samples, they measure many components of hemostasis (cellular, humoral, and fibrinolytic), thus identifying both hypocoagulable and hypercoagulable states and have been/ are being used to facilitate targeted transfusion strategies in trauma resuscitation, cardiothoracic surgery, and peri-liver transplant. As opposed to the traditional tests of coagulation, such as the prothrombin time (PT) and partial thromboplastin time (PTT) which are performed on platelet-poor serum, VHAs provide insight into Fawaz Al-Mufti, MD the interaction of platelets with the coagulation cascade (aggregation, clot strengthening, fibrin cross linking and fibrinolysis) are numerous time points during clot formation and dissolution. The VHA quantify and illustrate the mechanical resistance between whole blood clotting in a small cup and a pin that is suspended in the cup while either the cup (TEG®) or pin (ROTEM®) twists back and forth. The greater the torque or resistance on the pin, the greater the strength of the clot. As opposed to the PT and PTT, the test is not concluded when the clot has formed; the assay continues to run, demonstrating the inherent fibrinolytic characteristics of the sample. VHAs are largely point of care tests, and thus provide actionably information within 10 minutes of initiation. The entire assay takes 60-120 minutes to run. The tracing that is generated can be observed in real time remotely with the (TEG®) system. Drawbacks to the VHA include the need for calibration 2-3 times daily by trained personnel less making it susceptible to technical variations, the need for pipetting of reagents, and the sensitivity of the machines to motion and vibration. Newer generations of VHAs are in development that hope to overcome these limitations. As a functional test of clot formation and lysis, it is conceptually well-suited to monitor the progress or resolution of coagulopathy after injury hence TEG has been used to predict the need for as well as guidance of transfusion strategies (see tables for examples). Studies show cost-effectiveness and reduction in blood products in liver transplantation and cardiac surgery but it may also be useful in trauma (to reduce blood product use) and in the early detection of dilutional coagulopathy and injury induced hyperfibrinolysis. Results may be difficult to interpret in patients receiving LMWH, aspirin, anemia, following the use of fibrinolytics as well as those who are hypercoagulable or are post cardiac bypass. Christopher Zammit, MD NORMAL TEG PHASE AND TERMINOLOGY R value Reaction time(s) Time of latency from start of test to initial fibrin formation (amplitude of 2mm); i.e. initiation K Kinetics(s) Time taken to achieve a certain level of clot strength (amplitude of 20mm); i.e. amplification Alpha angle (Slope Between R and K) Measures the speed at which fibrin build up and cross linking takes place, hence assesses the rate of clot formation; i.e. thrombin burst TMA Time to maximum amplitude(s) MA Maximum Amplitude(mm) Represents the ultimate strength of the fibrin clot; i.e. overall stability of the clot A30 or LY30 Amplitude at 30 minutes; percentage decrease in amplitude at 30 minutes post-MA and gives measure of degree of fibrinolysis CLT Clot lysis time (s) 27


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