- Thromboelastography
Thromboelastography (TEG) is a method of testing the efficiency of
coagulation in theblood . It was first developed by the GermanDr. Hellmut Hartert at Medical University of Heidelberg. in 1948. It is especially important insurgery andanesthesiology .The original method
In classical thromboelastography, a small sample of blood (typically 0.36 ml) is placed into a
cuvette (cup) which is rotated gently through 4º 45´ (cycle time 6/min) to imitate sluggish venous flow and activate coagulation. When a sensor shaft is inserted into the sample a clot forms between the cup and the sensor. The speed and strength of clot formation is measured in various ways (now usually by computer), and depends on the activity of the plasmatic coagulation system,platelet function,fibrinolysis and other factors which can be affected by illness, environment and medications.The patterns of changes in strength and elasticity in the clot provides information about how well the blood can perform
hemostasis (the halting of blood flow), and how well or poorly different factors are contributing clot formation.Four values that represent clot formation are determined by this test: the R value (or reaction time), the K value, the angle and the MA (maximum amplitude). The R value represents the speed of clot formation (time until the first evidence of a clot is detected). The K value is the time from the end or R until the clot reaches 20mm and this represents the speed of clot formation. The angle is the tangent of the curve made as the K is reached and offers similar information to K. The MA a reflection of clot strength. A mathematical formula determined by the manufacturer can be used to determine a Coagulation Index (CI) (or overall assessment of coagulability) which takes into account the relative contribution of each of these 4 values into 1 equation. [Donahue SM, Otto CM, Thromboelastography: a tool for measuring hypercoagulability, hypocoagulability, and fibrinolysis, Journal of Veterinary Emergency and Critical Care:15(1), March 2005, Pages: 9-16]
Other methods
Rotation thromboelastometry or ROTEM (the name is a trademark of
Pentapharm ) is another version in which it is the sensor shaft rather than the cup which rotates. The shaft typically rotates back and forth 4º 45´ (cycle time 10/min). It is connected with a spring to measure elasticity. As the blood in the cuvette begins to clot there is a loss of elasticity in the spring causing changes in the rotation of the shaft. These changes are detected by the light reflected by the small mirror on the shaft and are converted by a transducer to electrical signals which are then measured by a computer.Pentapharm claims this opto-mechanical detection method makes this method more precise and less vulnerable to vibration and mechanical shocks than the classical method making the transportation and installation of the instrument very simple.
References
* Wenker, Olivier C.; Wojciechowski, Zbigniew; Sheinbaum, Roy; Zisman, Eli. [http://www.ispub.com/ostia/index.php?xmlFilePath=journals/ija/vol1n3/teg.xml "Thrombelastography"] . "The Internet Journal of Anesthesiology". 2000. Volume 1 Number 3.
* Whitten, Charles W. M.D.; Greilich, Philip E. M.D. [http://www.anesthesiology.org/pt/re/anes/fulltext.00000542-200005000-00008.htm;jsessionid=DXjpM23YXtXn5AtNCP0uY1Ln52P3vxF611MSsEekkmXVAAGrg2gl!-287926661!-949856145!9001!-1 "Thromboelastography: Past, Present, and Future"] . "Anesthesiology". 92(5):1226, May 2000.
* [http://www.rotem.de/index.php?id=50&L= Pentapharm GMBH: Thromboelastography]
* [http://vam.anest.ufl.edu/simulations/simulationportfolio.php Free simulation of a thromboelastograph (Requires Registration)]
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