Critical Care Medicine-Hematologic and Oncologic Disorders>>>>>Platelet Disorders
Question 1#

A 72-year-old male is admitted to the intensive care unit after undergoing aortic valve replacement for severe aortic stenosis. He was successfully weaned from bypass, required no blood products, and received appropriate protamine reversal. In the intensive care unit, he has been having persistent drainage from the thoracotomy tubes. A complete blood count (CBC) shows a hematocrit of 40% and platelet count of 150,000/mm3 . Coagulation studies including a thromboelastogram (TEG) are sent.

TEG results:

Based on the results of the TEG, which of the following would be the best treatment option?

A. Platelet
B. Protamine
C. Fibrinogen
D. Fresh Frozen Plasma

Correct Answer is A

Comment:

Correct Answer: A

Thomboelastogram, or TEG, is a whole blood, point-of-care test that analyses viscoelastic proprieties of evolving clot in the patient’s whole blood and can provide information about fibrin formation, platelet activation, and clot retraction, therefore assisting in identifying the cause of coagulopathy. Unlike the more traditional laboratory tests such as PT and PTT, which give a general state of the extrinsic and intrinsic pathways, TEG provides distinct values as well as a graphical representation of various stages in clot formation (Figure below). 

R-time is the duration of time from the application of the blood sample until the clot reaches a graphical amplitude of 2 mm, in other words, the time elapsed between clot formation and a predetermined and consistent size. The initiation of clot formation is dependent on circulating, function clotting factors from both the intrinsic and extrinsic pathways. A normal Rtime is 5 to 10 minutes, whereas a value less than 5 minutes implies hypercoagulability, and conversely, a value greater than 10 minutes indicates either a quantitative or qualitative deficiency in clotting factors. Treatment for prolonged R-time typically is Fresh Frozen Plasma, or factor concentrate in the setting of known factor deficiency (ie Hemophilia).

K-time represents the time elapsed between the conclusion of R-time and a graphical amplitude of 20 mm. Because the K-time is the duration between an initial amplitude (2 mm) and final amplitude (20 mm), this provides a quantitate assessment of the speed of clot formation. Thrombin catalyzes the conversion of fibrinogen to fibrin, which adheres the platelet plug, strengthening it, and finalizing the clot formation. A prolonged Ktime indicates inadequate circulating fibrin and is treated with either fibrinogen concentrate, or cryoprecipitate.

Alpha angle is a measurement of the speed of clot strengthening via fibrin cross-linking. It is formed by a tangential line originating from the start of K-time and intersecting the upward slope of the graph. A decreased alpha angle is similar to a prolongation of K-time and is treated in a similar manner.

MA is the greatest width between the two arms of the curve and represents overall clot strength. As the available platelets continue to form clot, which is subsequently stabilized by fibrin cross-links, the strength of the clot increases and the arms of the curve move farther apart. Eventually, the clot begins to degrade and the arms start sloping downwards. This transition point marks the MA. MA is a surrogate for platelet function, where a decreased MA suggests either inadequate supply (ie postcardiac bypass thrombocytopenia) or suboptimal function (ie liver disease). A decreased MA is treated with platelets.

This patient has a decreased MA suggesting poor clot strength likely from platelet deficiency. So, the best treatment option based on the TEG would be to administer platelets.

Sample TEG demonstrating normal coagulation morphology with normal values:

References:

  1. Scarpelini S, Rhind SG, Nascimento B, et al. Normal Range values for thromboelastography in healthy adult volunteers. Braz J Med Biol Res. 2009;42(12):1210-1217.
  2. Verma A, Hemlata. Thromboelastography as a novel viscoelastic method for hemostatis monitoring: its methodology, applications and constraints. Glob J Transfus Med. 2017;2:8-18.