The Thromboelastograph and the Thromboelastograph Technique

The thromboelastograph was originally described in 1948 by Hartert. I Work by Hartert and others in the 1950s evaluated the effect of clotting factor deficiencies, anticoagulants, thrombocytopenia, and fibrinolysis on the thromboelastograph and demonstrated that it could be used as a rapid empirical screen of overall hemostatic function. 2 The thromboelastograph has been used extensively in Europe for a number of years. Its availability was limited in the United States until the 1980s, when it underwent somewhat of a rebirth with its use during liver transplantation procedures.,4 The blood clot has both viscous and elastic properties. The thromboelastograph measures the elastic shear modulus or storage modulus of clotting blood. As originally described by Hartert, it is independent of sample viscosity over a wide range.s Figure 1 shows a diagram of the sample mechanism of the thromboelastograph and a typical thromboelastograph tracing. Whole blood is placed in the sample cup. A pin suspended by a calibrated torsion wire is lowered into the sample. To measure the elastic shear modulus of the sample, the cup is oscillated through an angle of 4° 45' over a 10-second interval, including 1 second rest periods at the end of the rotation in each direction to prevent viscosity errors. The torque of the cup is transmitted to the pin through the sample in the cup. The width of the tracing is proportional to the magnitude of elastic shear modulus of the sample. Liquid whole blood transmits little or no torque from cup to pin, producing no deflection on the tracing even when the whole blood viscosity is high (such as in polycythemia or macroglobulinemia). As the blood clots, fibers composed of platelets and fibrin form between the cup and pin, transmitting a portion of the cup's motion to the