Coagulation Flashcards
Primary hemostasis occurs within seconds after a vascular injury. Platelets become activated and adhere to the subendothelial collagen layer of the denuded vessel via glycoprotein receptors; this
interaction is stabilized?
von Willebrand’s factor (vWF)
Collagen and epinephrine activate
____ and ____ in the platelet plasma membrane, resulting in formation of _____ and degranulation, respectively.
Phospholipases A and C Thromboxane A2 (TXA2)
Instrinsic and extrinsic pathways mechanisms merge after formation of what clotting factor?
X
When a clot is formed, plasminogen is incorporated and then converted to plasmin by (2)?
1) Tissue plasminogen activator (tPA)
2) Fragments of factor XII
Coagulation inhibitors that are normally present in plasma (3)?
1) Antithrombin III
2) Proteins C and S
3) Tissue factor pathway inhibitor
Normal bleeding times range from __ to __
minutes, and a bleeding time >1.5 times normal (>15 minutes) is considered significantly abnormal.
4-9 minutes
The minimal recommended platelet count before surgery is?
75,000/mm3
Factor VIII is a large protein complex of two noncovalently bound factors (2)?
Factor VIII antigen and vWf
In vivo, coagulation is initiated primarily by contact of factor __ with extravascular tissue.
VII
The primary treatment for DIC is to?
Treat the underlying medical condition
What pathway is affected first by vitamin K deficiency?
Extrinsic
Because the factor with the shortest half-life is factor VII, found only in the extrinsic pathway.
Nice to know
The warfarin-like drugs compete with vitamin K for binding sites on the hepatocyte.
Administration of subcutaneous vitamin K reverses the functional deficiency in 6 to 24 hours.
With active bleeding or in emergency surgery, fresh frozen plasma (FFP) can be administered for immediate hemostasis.
The half-life of heparin’s anticoagulant effect is about ___ minutes in a normothermic patient.
90 minutes
Heparin is a polyanionic mucopolysaccharide that accelerates the interaction between _____ and the activated forms of factors (5)?
antithrombin III
II, X, XI, XII, and XIII
This test adds fresh whole blood to a test tube already containing an activator. It is widely used to monitor heparin therapy in the operating room. The normal range is 90 to 120 seconds.
Activated clotting time
A test that measures the extrinsic and common pathways. Tissue thromboplastin is added to the patient’s plasma.
Prothrombin time (PT)
A test was introduced to improve the consistency of oral anticoagulant therapy.
International normalized ratio (INR)
What are the indications for administering fresh frozen plasma?
When microvascular bleeding is noted and PT or PTT exceeds 1.5 the control value, FFP should be considered. The usual dose is 10 to 15 ml/kg. FFP will also reverse the anticoagulant effects of warfarin (5 to 8 ml/kg).
Administration of vitamin K will have the same result as FFP but will take how many hours take effect?
6-12 hours
It is the cold-insoluble white precipitate formed when FFP is thawed. It contains what clotting factors?
Cryoprecipitate
VIII, vWf, fibrinogen, XIII
One unit of cryoprecipitate per 10 kg of body weight will increase fibrinogen levels by ___ mg/dl
50
Cryoprecipitate lacks what factor?
V
The basic difference between the intrinsic and extrinsic pathways is the phospholipid surface. What is found in extrinsic?intrinsic?
platelet phospholipid (intrinsic pathway) tissue thromboplastin (extrinsic pathway)
What measures the instrinsic pathway?
PTT measures the clotting ability of all factors in the intrinsic and common pathways except factor XIII
Describe the activated partial thromboplastin time.
Maximal activation of the contact factors (XII and XI) eliminates the lengthy natural contact activation phase and results in more consistent and reproducible results.
This is a neoantigen formed by the action of thrombin in converting fibrinogen to cross-linked fibrin.
D-dimer
It measures the viscoelastic properties of blood as it is induced to clot in a low shear environment resembling venous flow, providing some measure of clot strength and stability, including the time to initial clot formation, the acceleration phase, strengthening, retraction, and clot lysis.
Thromboelastography (TEG)
Discuss the parameters measured by thromboelastography. There are five parameters of the TEG tracing?
1) R
2) k
3) alpha angle
4) MA
5) MA60
Thromboelastography parameter that time from the initiation of the test to initial fibrin formation?
R
Time from the beginning of clot formation until the amplitude of TEG reaches 20 mm, representing the dynamics of clot formation
k
Angle between the line in the middle of the TEG tracing and the line tangential to the developing body of the tracing, representing the kinetics of fibrin
cross-linking
alpha angle
Reflects the strength of the clot, which depends on the
number and function of platelets and their interaction with fibrin.
MA (maximum amplitude)
Measures the rate of amplitude reduction 60 minutes after MA, representing the stability of the clot
MA60
