Article for ASCLS-IN Coagulation SA

Thromboelastography and Thromboelastometry

What’s Old is New Again

George A. Fritsma, MS MLS
The Fritsma Factor, Your Interactive Hemostasis Resource
www.fritsmafactor.com; george@fritsmafactor.com

 

The Thromboelastograph® (TEG®, Haemonetics® Corporation, Braintree, MA) was developed in Germany during World War II and was first described in scientific literature by Professor Helmut Hartert in 1948.[1] The instrument has been employed virtually unchanged, except for its 1978 modification from a paper to a computer graph, and has since lent its name to the science of thromboelastography (figure 1).[2] Thromboelastography is widely employed by anesthetists and surgeons to monitor coagulation factor deficiency, heparin therapy, platelet function, and fibrinolysis during coronary artery bypass graft surgery or cardiac catheterization (percutaneous intervention). Since 2000, thromboelastography has grown vital to the management of coagulopathy secondary to shock and massive hemorrhage in trauma and surgery.[3]

figure 1 2.1.2.A CopyingOurGenes-5  fugure 2
Figure 1, Thromboelastograph Figure 2, ROTEM

In 1997, Andreas Calatzis, MD and physicist Pablo Fritzche, PhD developed an enhanced form of thromboelastography, the rotational elastometer (ROTEM®, Pentapharm® AG, Basil, Switzerland and TEM Systems®, Inc., Durham, NC), leading to a parallel term, thromboelastometry (TEM, figure 2).[4] TEG and TEM are collectively named viscoelastometry or viscoelastic testing, though neither of these latter terms appears in the PubMed Medical Subject Headings list. The ROTEM is now a worldwide TEG competitor.[5]

 

TEG and ROTEM Operation

The TEG is able to test freshly collected whole blood, however, for the sake of convenience, both the TEG and ROTEM are customarily employed to test whole blood collected in 3.2% sodium citrate. The ROTEM can also assay platelet rich or platelet poor plasma. The TEG sample volume is 360 µL and the ROTEM requires 340 µL. The TEG performs two assays simultaneously, the ROTEM performs four. The ROTEM is equipped with semiautomated pipettors.

The TEG employs a warmed 1 mL disposable cylindrical sample cup into which is suspended a disposable cylindrical pin. The cup oscillates for ±4°45’ at 6-second intervals and the pin is free in the cup, suspended from a torsion wire. The outer surface of the pin resides within 1 mm of the inner surface of the cup (figure 3). Conversely, the ROTEM cup remains stationary while the pin, mounted in ball bearings, oscillates for ±4°45’ every 6 seconds, same as the TEG (figure 4). Like the TEM, the distance from ROTEM cup surface to pin is also 1 mm. The ROTEM configuration provides for greater operating stability.

 figure 3  figure 4
Figure 3: TEG Principle. The sample cup oscillates and as the clot forms, the pin begins to oscillate in proportion to clot elasticity. An electromagnetic detector senses and records torsion wire movement. Figure 4: ROTEM Principle. The sample cup remains stationary as the sensor pin oscillates. Clot-induced sensor pin oscillation force changes are detected using an LED light source and detector. The changes are recorded in a computer file.

The operator initiates coagulation with the addition of a reagent to the sample, whereupon the viscosity of the developing fibrin clot generates a growing physical association between cup and pin. The rate of clot formation and its elastic strength affect the magnitude of pin oscillation, which rises in the TEG and diminishes in the ROTEM. In the TEG, a magnetic-electrical transducer converts pin oscillation to an electrical signal from which the computer renders a graph and computes quantitative parameters. In the ROTEM, an LED-based optical detection system generates an electrical signal that results in a similar graph but with dissimilar mathematical parameters. As clot lysis occurs and continues over 20–30 minutes, elastic strength is lost; this decrease in viscosity is reflected in the narrowed tracing and a changing numerical output. The operator evaluates the output to deduce clotting and fibrinolytic adequacy. Figure 5 represents a normal TEG and ROTEM tracing.

The TEG operator may introduce fresh un-anticoagulated blood within 3 minutes of collection directly to the cup but is more likely to employ citrated blood. In the latter event, the operator may simply pipette calcium chloride to the anticoagulated whole blood specimen. Alternatively, the TEG operator may first treat the specimen with kaolin, a negatively charged particulate factor XII activator, or a preparation of tissue factor that activates factor VII. This additional step makes the output more practical as it shortens the R and K times. The ROTEM operator may use up to five activators, EXTEM®, INTEM®, FIBTEM®, APTEM®, and HEPTEM®. Details of these activators are provided in table 2.

Interpretation

Figure 5 and table 1 represent normal TEG and ROTEM tracings and typical reference intervals when clotting is triggered using kaolin or the INTEM® reagent. Reference intervals vary widely with test platform and reagent; each institution establishes local reference intervals. TEG and ROTEM are particularly useful when monitoring treatment in trauma or surgery involving massive hemorrhage and in monitoring heparin therapy during coronary artery bypass graft surgery or cardiac catheterization.

Several studies that originated in the treatment facilities of the Iraq war have been extended to civilian trauma centers around the world in the PROMMT study.[6],[7] These findings have profoundly modified the management of trauma-induced coagulopathy and the coagulopathy of severe hemorrhagic surgical blood loss.[8] The key to improved mortality rates is the clinical management of the conditions that define shock: acidosis, hypothermia, and hypotension; while simultaneously managing the inevitable coagulopathy. In place of colloids or crystalloids, surgeons and emergency personnel now employ plasma, platelets, and packed RBCs in equal proportions. Further, the European CRASH-2 study, which awaits duplication, recommends concentrates in place of plasma, in particular, prothrombin complex concentrate and fibrinogen concentrate or cryoprecipitate.[9] These may be supplemented with antifibrinolytics, thereby reducing the volume of therapeutic fluids and reducing the risk of transfusion-associated circulatory overload. The selection of therapies is guided by TEM or ROTEM parameters, as illustrated in table 1.

The R-value (ROTEM’s CT) is prolonged beyond the upper limit of the reference interval by heparin therapy or single or multiple coagulation deficiencies, including fibrinogen deficiency. Figure 6 illustrates a prolonged R-value. The R-value is reflected in the K-value (CFT) and the a-value, and the condition may be treated with fibrinogen concentrate, cryoprecipitate, prothrombin complex concentrate, or thawed plasma. The R-value (CT) is also used to monitor the effect of unfractionated or low molecular weight heparin therapy and to measure heparin reversal with protamine sulfate.

An MA (MCF) less than the lower RI limit reflects a weak fibrin clot caused by a platelet function abnormality, thrombocytopenia, or the effect of an anti-platelet drug like aspirin or clopidogrel (figure 6). Platelet concentrate is a first-line therapy in massive hemorrhage, and may be monitored using the MA (MCF).

If the CL30 or LY30 is increased (figure 6), hyperfibrinolysis may be treated with tranexamic acid (Cyklokapron) or epsilon amino-caproic acid (EACA).

Table 1: TEG and ROTEM Quantitative Parameters[10],[11].

TEG ROTEM Approximate RI Interpretation
R-time CT 19–28 mm; 4–10 minutes Prolonged or increased by an anticoagulant or any single or multiple clotting factor deficiency, thrombocytopenia, or by a platelet function abnormality
K-time CFT 8–13 mm; 1–3 minutes
a-angle a 29–64°
MA MCF 48–67 mm Strength of fibrin clot, which is decreased by anticoagulant therapy, thrombocytopenia or platelet function abnormality
CL 30 LY 30 94–98% of MCF < 94% indicates hyperfibrinolysis
CL 60 LY 60 >15% of MCF < 15% indicates hyperfibrinolysis
RI, reference interval; R or CT, reaction or clotting time; K or CFT, clot formation time; MA, maximum amplitude; MCF, maximum clot formation; a, rate of clot formation; CL 30 or LY 30, clot lysis % at 30”; CL 60 or LY 60, clot lysis % at 60”

 

figure 5  figure 6
Figure 5: Normal tracing representing a 60-minute assay; TEG parameters R, K, a, MA, CL30 and CL60 on top; ROTEM parameters CT, CFT, a, MCF, LY30, and LY60 on the bottom.  Figure 6: TEG or ROTEM tracings. Thrombocytopenia, antiplatelet drugs, or platelet function disorders suppresses the MA (MCF). Coagulation factor deficiencies or heparin therapy prolong the R (CT) and the K (CFT), and reduce the a-angle. Fibrinolysis is reflected in a narrowed tracing that follows normal coagulation, and is reflected in an increased LY30.

The ROTEM offers several activators, each with its own reference intervals and interpretation, listed in tables 2 and 3. The EXTEM and INTEM reagents respectively parallel tissue factor and particulate activator and activate coagulation at the level of factors VII and XII. FIBTEM is an EXTEM reagent that incorporates cytochalasin D, a platelet inhibitor, thus the CT, CFT, and a values reflect fibrinogen activity independent of platelet function. The APTEM reagent is an EXTEM reagent modified to include aprotinin, a fibrinolysis inhibitor, enabling the operator to assess fibrinolysis within ten minutes by comparing to the EXTEM response. Finally, HEPTEM is the INTEM reagent modified with heparinase, which enables the operator to perform a full ROTEM analysis on a heparinized specimen.

Table 2: ROTEM test parameters.

EXTEM Tissue factor reagent activates at the level of factor VII Assesses activity of factors VII, X, V, II, and fibrinogen, platelets, and fibrinolysis, clot is assessed in 10 m.
INTEM Negatively charged particulate activator activates at level of factor XII Assesses activity of factors XII, HMWK, PK, XI, IX, VIII, X, V, II, fibrinogen, platelets, and fibrinolysis
FIBTEM EXTEM reagent with cytochalasin D platelet inhibitor Blocks platelet activation, measures fibrinogen and fibrin polymerization independent of platelet function
APTEM EXTEM reagent with aprotinin fibrinolysis inhibitor Enables operator to detect hyperfibrinolysis in 10 minutes by comparing result to EXTEM result
HEPTEM INTEM reagent with heparinase When compared to INTEM, enables operator to perform the ROTEM analysis in heparinized specimens

 

Table 3: ROTEM Reference Intervals

  CT CFT MCF LY 60
EXTEM 35–80 s 35–150 s 53–72 mm > 15% of MCF
INTEM 100–240 s
HEPTEM
APTEM 35–80 s 35–160 s
FIBTEM 8–20 mm

Summary

The TEG and the ROTEM are point of care laboratory instruments that are managed predominantly by anesthetists. They are found in operating suites and emergency departments worldwide. Though the TEM and ROTEM employ time-honored technology, their applications have expanded to managing massive hemorrhage of trauma and surgery, and they are likely to grow in acceptance as their value for this application gains a toehold in surgical suites and emergency departments. Though not maintained in the “central” laboratory, medical laboratory personnel maintain primary responsibility for their operation, validation, and interpretation.

References

[1] Hartert H. Blutgerinnungsstudien mit der thrombelastographie, einem neuen untersuchungsvefahren. Klinische Wochenschrift 1948;26:577–83.

[2] Raviv G, Cramer DB, Epstein M, Zukerman L, Caprini JA. Computerization of three-channel thrombelastograph. J Med. 1978;9:33–41.

[3] McDaniel LM, Etchill EW, Raval JS, Neal MD. State of the art: massive transfusion. Transfusion Medicine 2014;24:138–44.

[4] Ingerslev J, Christiansen K, Calatzis A, Holm M, Sabroe Ebbesen L. Management and monitoring of recombinant activated factor VII. Blood Coagul Fibrinolysis. 2000;11 Suppl 1:S25–30.

[5] Jackson GNB, Ashpole KJ, Yentis SM. The TEG® vs the ROTEM® thromboelastography/ thromboelastometry systems. Anaesthesia 2009;64:212–15.

[6] Eastridge BJ, Jenkins D, Flaherty S, Schiller H, Holcomb JB. Trauma system development in a theater of war: experiences from Operation Iraqi Freedom and Operation Enduring Freedom. J Trauma. 2006;61:1366–72.

[7] Holcomb JB, Donathan DP, Cotton BA, et al. Prehospital transfusion of plasma and red blood cells in trauma patients. Prehosp Emerg Care. 2015;19:1–9.

[8] Holcomb JB, Tilley BC, Baraniuk S, et al. Transfusion of plasma, platelets, and red blood cells in a 1:1:1 vs a 1:1:2 ratio and mortality in patients with severe trauma: the PROPPR randomized clinical trial. JAMA. 2015;313:471–82.

[9] Edwards P, Shakur H, Barnetson L, Prieto D, Evans S, Roberts I. Central and statistical data monitoring in the clinical randomisation of an antifibrinolytic in significant haemorrhage (CRASH-2) trial. Clin Trials. 2013;11:336–43.

[10] Scarpelini S, Rhind SG, Nascimento B, et al. Normal range values for thromboelastography in healthy adult volunteers. Braz J Med Biol Res. 2009;42:1210–7.

[11] Edwards RM, Naik-Mathuria BJ, Gay AN, Olutoye OO, teruya J. Parameters of thromboelastograph in healthy newborns. Am J Clin Pathol 2008;130:99–102.

Prof. Fritsma manages www.fritsmafactor.com, “The Fritsma Factor, Your Interactive Hemostasis Resource,” an educational blog sponsored by Precision BioLogic Inc, Dartmouth, Nova Scotia.

Prof. Fritsma chairs the ASCLS Education and Research Fund and the AACC Press Board. He is an author for Rodak’s Hematology, 5th edition, 2015, Elsevier; and for Quick Guide to Coagulation 3rd Edition, 2015, Quick Guide to Hematology Testing, 2nd Edition, 2013; Quick Guide to Laboratory Statistics and Quality Control, 2012; Quick Guide to Renal Disease Testing, 2011; and Quick Guide to Venipuncture, 2010; published by AACC Press.

George holds a bachelor’s in biology and chemistry from Calvin College, Grand Rapids, Michigan, a Masters in Medical Technology from Wayne State University, Detroit, and advanced course work from the University of Illinois at Chicago.

Posted July 28, 2015 by ASCLS-IN

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