THROMBOELASTOGRAPHY

VISHNU AMBAREESH

• In surgery we have to manage patients with a bleeding diathesis in the preoperative, intraoperative or postoperative period.

• Complex surgical procedures including cardiac and liver surgery are associated with a potential for significant perioperative blood loss and the development of post operative bleeding disorders.

• inherent risks of the use of homologous blood and blood products, and allied to the scarcity of these resources, make it important that treatment with blood products is based on scientific evidence of need.

• A variety of coagulation tests are used to assess whole blood coagulation.

COAGULATION MONITORINGConventional tests

•Tests of coagulation

*Platelets• number• function

*Clotting studies• PT• APTT

*Fibrinogen levels

•Tests of fibrinolysis

* degradation products

• Each of these tests measures a different aspect of the clotting

process, but even in combination they do not provide a complete

picture of the status of the coagulation system

• Besides evaluation of platelet function remains insensitive and

time consuming. The platelet count provides only a

quantitative, not qualitative index of platelet status.

• At present the treatment of postoperative bleeding remains empirical because of the perceived need for immediate correction of the haemostatic defect and lack of readily available measures of all phases of clot formation and breakdown , including the strength of the clot

• FFP and platelets often given with little scientific basis.

What we need?

an effective and convenient means of monitoring whole blood coagulation

which evaluates the elastic properties of whole blood and provides a global

assessment of heamostatic function.

THROMBOELASTOGRAPHY

• First developed by Dr. Hellmut Hartet at University of Heidelberg, School of Medicine in 1948 as a method to assess global haemostatic function from a single blood sample; this was the original thromboelastography

WHAT IS THROMBOELASTOGRAPHYFunctional Description

• Thromboelastography monitors the

thrombodynamic properties of blood as it is

induced to clot under a low shear

environment resembling sluggish venous

flow. The patterns of change in shear-

elasticity enable the determination of the

kinetics of clot formation and growth as well

as the strength and stability of the formed

clot.

• The strength and stability of the clot provide information about the ability of the clot to perform the work of haemostasis, while the kinetics determine the adequacy of quantitative factors available to clot formation

• In classical thrombelastography, 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)

• 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.

THROMBOELASTOGRAPHYBasic Principles

• Heated (37C) oscillating cup

• Pin suspended from torsion wire into blood

• Development of fibrin strands “couple” motion of cup to pin

• “Coupling” directly proportional to clot strength

• tension in wire detected by EM transducer

THROMBOELASTOGRAPHYBasic Principles

• Electrical signal amplified to create TEG trace

• Result displayed graphically on pen & ink printer or computer screen

• Deflection of trace increases as clot strength increases & decreases as clot strength decreases

THROMBOELASTOGRAPHYRefinements to Technique

• TEG accelerants / activators / modifiers• Celite / Kaolin / TF accelerates initial coagulation

• Reopro (abciximab) blocks platelet component of coagulation

• Platelet mapping reagents modify TEG to allow analysis of Aspirin / Clopidigrol effects

• Heparinase cups• Reverse residual heparin in sample• Use of paired plain / heparinase cups allows

identification of inadequate heparin reversal or sample contamination

THROMBOELASTOGRAPHYThe “r” time

r time•represents period of time of latency from start of test to initial fibrin formation

•in effect is main part of TEG’s representation of standard”clotting studies”

•normal range• 15 - 23 mins (native

blood)• 5 - 7 mins (kaolin-

activated)

THROMBOELASTOGRAPHYWhat affects the “r” time?

•r time by• Factor

deficiency • Anti-

coagulation• Severe

hypofibrinogenaemia

• Severe thrombocytopenia

•r time by• Hypercoagula

bility syndromes

THROMBOELASTOGRAPHYThe “k” time

k time•represents time taken to achieve a certain level of clot strength (where r time = time zero ) - equates to amplitude 20 mm

•normal range• 5 - 10 mins (native

blood)• 1 - 3 mins (kaolin-

activated)

THROMBOELASTOGRAPHYWhat affects the “k” time?

•k time by• Factor deficiency • Thrombocytopeni

a• Thrombocytopath

y• Hypofibrinogenae

mia

•k time by• Hypercoagula

bility state

THROMBOELASTOGRAPHYThe “” angle

angle•Measures the rapidity of fibrin build-up and cross-linking (clot strengthening)•assesses rate of clot formation

•normal range• 22 - 38 (native

blood)• 53 - 67(kaolin-

activated)

THROMBOELASTOGRAPHYWhat affects the “” angle?

• Angle by• Hypercoagula

ble state

• Angle by• Hypofibrinogen

emia• Thrombocytope

nia

THROMBOELASTOGRAPHYThe “maximum amplitude” (MA)

Maximum amplitude •MA is a direct function of the maximum dynamic properties of fibrin and platelet bonding via GPIIb/IIIa and represents the ultimate strength of the fibrin clot

•Correlates to platelet function• 80% platelets• 20% fibrinogen

•normal range• 47 – 58 mm (native

blood)• 59 - 68 mm (kaolin-

activated)

THROMBOELASTOGRAPHYWhat affects the “MA” ?

•MA by• Hypercoagula

ble state

•MA by• Thrombocytope

nia• Thrombocytopa

thy• Hypofibrinogen

emia

THROMBOELASTOGRAPHYFibrinolysis

•LY30•measures % decrease in amplitude 30 minutes post-MA •gives measure of degree of fibrinolysis•normal range

• < 7.5% (native blood)

• < 7.5% (celite-activated)

•LY60• 60 minute

post-MA data

THROMBOELASTOGRAPHYOther measurements of Fibrinolysis

•A30 (A60)• amplitude at 30 (60) mins post-MA•EPL•earliest indicator of abnormal lysis•represents “computer prediction” of 30 min lysis based on interrogation of actual rate of diminution of trace amplitude commencing 30 secs post-MA

•early EPL>LY30 (30 min EPL=LY30)•normal EPL < 15%

THROMBOELASTOGRAPHYWhat measurements are affected by

fibrinolysis?

•Fibrinolysis leads to:• LY30 / LY60 • EPL• A30 / A60

THROMBOELATOGRAPHYQuantitative analysis

• Clot formation– Clotting factors - r, k times

• Clot kinetics– Clotting factors - r, k times– Platelets - MA

• Clot strength / stability– Platelets - MA– Fibrinogen - Reopro-mod

MA

• Clot resolution– Fibrinolysis - LY30/60; EPL A30/60

THROMBOELATOGRAPHYQualitative analysis

TEG v CONVENTIONAL STUDIES

• Conventional tests

• test various parts of coag cascade, but in isolation

• out of touch with current thoughts on coagulation

• plasma tests may not be accurate reflection of what actually happens in patient

• difficult to assess platelet function

• static tests• take time to complete

best guess or delay treatment

• TEG• global functional

assessment of coagulation / fibrinolysis

• more in touch with current coagulation concepts

• use actual cellular surfaces to monitor coagulation

• gives assessment of platelet function

• dynamic tests• rapid results rapid

monitoring of intervention

Advantages of TEG over conventional coagulation monitoring

• It is dynamic, giving information on entire coagulation process, rather than on isolated part

• It gives information on areas which it is normally difficult to study easily – fibrinolysis and platelet function in particular

• Near-patient testing means results are rapid facilitating appropriate intervention

• It is cost effective compared to conventional tests

ROTEM

• Rotational thromboelastography uses a modification of TEG, signal of the pin is transmitted using an optical detecter instead a torsion wire.

• Movement orginates from pin and not the cup• Uses an electronic pippette which improves

reproducibility and performance

• In ROTEM the sensor shaft rotates rather tha the cup

• avoids limitations of traditional instruments esp. susceptibility to mechanical shocks and vibrations.

• However TEG is rated as the best compromise between usability, usefulness and cost as compared to ROTEM

SONOCLOT

• Sonoclot incorporates a very sensitive visco-elastic detection system which is

very sensitive to the changes in the developing clot. It gives more detailed

information as compared to Thromboelastograph

• PRINCIPLE measures the changing impedence to

movement imposed by the developing clot on a small probe vibrating at an ultrasonic frequency in a coagulating blood sample.

THANK YOU!!!!