Thromboelastography

A 58-year-oldmale patient is recovering on the cardiac intensive care unit following first timecoronary bypass grafting. The surgeon is concerned that the drain output is greater than acceptable. You take a blood sample for thromboelastography. Which of the following findings would be consistent with a diagnosis of thrombocytopaenia?

a) A prolonged r time, an increased k time, a decreased alpha angle, a decreased MA

b) A normal r time, an increased k time, a normal alpha angle, an extremely decreased

MA

c) A decreased r time, a decreased k time, an increased alpha angle, an increased MA

d) A normal r time, a normal k time, an increased alpha angle, a continuously

decreasing MA

e) A prolonged r time, a normal k time, an increased alpha angle, a normal MA

Answer: B

Explanation

The thromboelastograph (TEG) measures how the shear elasticity of a blood sample

changes as a clot is formed. Measurements of strength and stability give an idea

whether the clot will do the job of haemostasis, and the kinetics of clot formation

give a quantitative indication of whether the patient has sufficient factors for clot

formation. Five parameters are measured by the basic TEG. The ‘r’ is the time from

start of the test to initial fibrin formation. The ‘k’ is the time from beginning of clot

formation until the amplitude reaches 20mm, the ‘alpha angle’ is the angle between the

middle of the TEG and a line drawn along the main body of the developing TEG trace.

This represents the acceleration of the fibrin burst. The ‘MA’ is the maximum amplitude

and represents how strong the clot is. The Ly30 is the amplitude 30 minutes

after the MA. This represents how stable the clot is. Typically, in a patient with low

platelets, the TEG would show a normal r time, an increased k time, a normal alpha

angle, and an extremely decreased MA. A prolonged r time, an increased k time,

a decreased alpha angle and a decreased MA is typical of blood clotting factor

deficiency. A decreased r time, a decreased k time, an increased alpha angle and an

increased MA is found in hypercoagulable states. A normal r time, a normal k time,

an increased alpha angle and a continuously decreasing MA is found in thrombolysis.

The final option given is not a typical pattern.

Reference

Curry A, Pierce T. Conventional and near-patient tests of coagulation. Contin Educ

Anaesth Crit Care Pain 2007; 7(2): 45–50.