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.Stability	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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