Viscoelastic haemostatic assays:

 

How it works:

Old method

·     Blood and reagent in cup

·     Cup rotates around pin or vice versa

·     Blood sticks to pin and makes it move

New method

·     Measure change in resonant frequency of blood as it clots

·     The rest is the same

 

Parameters:

Aspect

TEG

ROTEM

Definition

Product

1.Speed

R time

CT

Time to 2mm

FFP

2.Strength

K time

CFT

Time to 20mm

Fibrinogen

Platelets

α-angle

α-angle

Gradient at K time (sort of)

MA

MCF

Max amplitude

3.Duration

LY30

CLI30

Amplitude at 30 mins after max

TXA

N.B. there is good correlation between maximum amplitude and amplitude at 5 and 10 mins.

 

Assays:

TEG

ROTEM

Key ingredient

Function

CK

INTEM

Kaolin

Intrinsic pathway clot

CRT

EXTEM

Tissue factor

Extrinsic pathway clot

CFF

FIBTEM

Anti-platelet

Fibrinogen-only clot

???

APTEM

Antifibrinolytic

Clot without fibrinolysis

CKH

HEPTEM

Heparinase

Clot once reversed

 

Approach:

1.RBC

·      Hb >60

2.TXA

·      Give empirically

·      Anti-fibrinolytic clot: normal taper

·      Other assays: fast taper

3.Cryo

·      Extrinsic pathway clot: ↓ strength

·      Fibrinogen-only clot: ↓ strength                 (1) FIBTEM A5 <12mm

4.Platelets

·      Extrinsic pathway clot: ↓ strength             (2) EXTEM A5 <35mm

·      Fibrinogen-only clot: ↔ strength

5.FFP

·      Intrinsic pathway clot: ↑delay                    (3) EXTEM CT >80sec

 

Acronyms:

TEG parameters

R time = reaction time

K time = koagulation time

MA = max amplitude

LY30 = lysis at 30 minutes

TEG assays

CK = citrated kaolin

CRT = citrated rapid TEG

CFF = citrated functional fibrinogen

ROTEM parameters

CT = clotting time

CFT = clot formation time

MCF = maximum clot firmness

CLI30 = clot lysis index at 30 mins

ROTEM assays

INTEM

EXTEM

FIBTEM

APTEM = aprotinin-containing

HEPTEM

 

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