Principles and Practice of Thromboelastography in Clinical Coagulation Management and Transfusion Practice

Working principle of TEG (panel A) and ROTEM (panel B). In TEG, the cup with the blood sample is rotating, whereas the torsion wire is fixed. In ROTEM, the cup is fixed, whereas the pin is rotating. Changes in torque are detected electromechanically in TEG and optically in ROTEM. The computer-processed signal is finally presented as a tracing. Panel C shows typical tracings from TEG (lower tracing) and ROTEM (upper tracing). For a detailed description of the terms used and the reference values of the various thromboelastographic parameters, see .

ROTEM tracings from a patient undergoing cardiac surgery at baseline (panel A) after severe dilution (panel B) during cardiopulmonary bypass and after substitution with cryoprecipitate (panel C). EXTEM and FIBTEM traces are overlaid. Platelet counts (10³/μL), fibrinogen levels (milligram per deciliter), and hematocrit (percentage) are depicted for each time point. After substitution with cryoprecipitate, the EXTEM tracing normalizes because of the increase of fibrinogen levels (also evident in the FIBTEM tracing). Because of lower hematocrit, FIBTEM is much larger despite similar fibrinogen values at baseline and after cryoprecipitate substitution. PLT indicates platelet count; FIB, fibrinogen level; HCT, hematocrit.

Typical traces of thromboelastography (the gray trace) and thrombin generation (the black trace). The dotted vertical line indicates where the conventional coagulation tests (PT/aPTT) stop in relation to thrombin generation and thromboelastography.

The FIBTEM amplitude depends not only on the fibrinogen level but also on the hematocrit. The graphs shown are derived from an in vitro study in whole blood from 4 healthy patients (unpublished data). The FIBTEM amplitude after 15 minutes decreases with increasing dilution with saline (NaCl) because of decreasing fibrinogen levels but increases when the whole blood is diluted with autologous plasma (fibrinogen levels remain unchanged). The latter finding is explained by decreased hematocrit.

Typical EXTEM (panels A and C) and FIBTEM (panel B) traces in undiluted whole blood showing clot retraction (panel A) and hyperfibrinolysis (panel C). Panel A shows no fibrinolysis, but clot retraction is evident by the missing fibrinolysis in the FIBTEM test (panel B). Panel C shows hyperfibrinolysis after in vitro addition of tPA.

A proposed transfusion algorithm in bleeding patients based on conventional coagulation and ROTEM parameters. For an explanation of the abbreviations of the ROTEM parameters, please refer to Table 1.