Thromboelastography
Encyclopedia
Thrombelastography is a method of testing the efficiency of coagulation
in the blood
. It was first developed by the German Dr. Hellmut Hartert at University of Heidelberg School of Medicine in 1948. It is especially important in surgery
and anesthesiology.
(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. If there is suspicion that the blood will have difficulty clotting (either through medication or disease) then the blood may be exposed to a thrombosis-inducing agent (such as kaolin) immediately prior to the start of the test.
The patterns of changes in strength and elasticity in the clot provide information about how well the blood can perform hemostasis
(the halting of blood flow), and how well or poorly different factors are contributing to 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 time until the first evidence of a clot is detected. The K value is the time from the end of 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 is 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.
The classical method is used in the TEG (the name is a trademark of Haemoscope Corp. USA) and in the ThromboElastoMeter-Automated (TEM-A).
or ROTEM (the name is a trademark of Tem Innovations GmbH, Munich) is another version in which it is the sensor shaft rather than the cup which rotates.
Blood (300 µl, anticoagulated with citrate
) is placed into the disposable cuvette using an electronic pipette. A disposable pin is attached to a shaft which is connected with a thin spring (the equivalent to Hartert’s torsion wire in thrombelastography) and slowly oscillates back and forth. The signal of the pin suspended in the blood sample is transmitted via an optical detector system. The test is started by adding appropriate reagents. The instrument measures and graphically displays the changes in elasticity at all stages of the developing and resolving clot. The typical test temperature is 37°C, but different temperatures can be selected, e.g. for patients with hypothermia.
In contrast to thrombelastography with its pendulum-like principle, the design of the TEM viscoelastic detection system (figure 1) makes it quite robust and insensitive against mechanical shocks or vibrations, making the transportation and installation of the instrument very simple.
Coagulation
Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
in the blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
. It was first developed by the German Dr. Hellmut Hartert at University of Heidelberg School of Medicine in 1948. It is especially important in surgery
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
and anesthesiology.
The original method
In classical thrombelastography, a small sample of blood (typically 0.36 ml) is placed into a cuvetteCuvette
A cuvette is a small tube of circular or square cross section, sealed at one end, made of plastic, glass, or fused quartz and designed to hold samples for spectroscopic experiments. The best cuvettes are as clear as possible, without impurities that might affect a spectroscopic reading...
(cup) which is rotated gently through 4º 45´ (cycle time 6/min) to imitate sluggish venous flow
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
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
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
coagulation system, platelet
Platelet
Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days...
function, fibrinolysis
Fibrinolysis
Fibrinolysis is a process that prevents blood clots from growing and becoming problematic. This process has two types: primary fibrinolysis and secondary fibrinolysis...
and other factors which can be affected by illness, environment and medications. If there is suspicion that the blood will have difficulty clotting (either through medication or disease) then the blood may be exposed to a thrombosis-inducing agent (such as kaolin) immediately prior to the start of the test.
The patterns of changes in strength and elasticity in the clot provide information about how well the blood can perform hemostasis
Hemostasis
Hemostasis or haemostasis is a process which causes bleeding to stop, meaning to keep blood within a damaged blood vessel . Most of the time this includes blood changing from a liquid to a solid state. Intact blood vessels are central to moderating blood's tendency to clot...
(the halting of blood flow), and how well or poorly different factors are contributing to 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 time until the first evidence of a clot is detected. The K value is the time from the end of 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 is 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.
The classical method is used in the TEG (the name is a trademark of Haemoscope Corp. USA) and in the ThromboElastoMeter-Automated (TEM-A).
Other methods
Rotational thromboelastometryThromboelastometry
Thromboelastometry is an established viscoelastic method for haemostatis testing in whole blood. TEM investigates the interaction of coagulation factors, their inhibitors, anticoagulant drugs, blood cells, specifically platelets, during clotting and subsequent fibrinolysis...
or ROTEM (the name is a trademark of Tem Innovations GmbH, Munich) is another version in which it is the sensor shaft rather than the cup which rotates.
Blood (300 µl, anticoagulated with citrate
Citrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...
) is placed into the disposable cuvette using an electronic pipette. A disposable pin is attached to a shaft which is connected with a thin spring (the equivalent to Hartert’s torsion wire in thrombelastography) and slowly oscillates back and forth. The signal of the pin suspended in the blood sample is transmitted via an optical detector system. The test is started by adding appropriate reagents. The instrument measures and graphically displays the changes in elasticity at all stages of the developing and resolving clot. The typical test temperature is 37°C, but different temperatures can be selected, e.g. for patients with hypothermia.
In contrast to thrombelastography with its pendulum-like principle, the design of the TEM viscoelastic detection system (figure 1) makes it quite robust and insensitive against mechanical shocks or vibrations, making the transportation and installation of the instrument very simple.