Coagulation Flashcards
Homeostasis means
Hemostasis is the ability of the body’s systems to maintain the integrity of the blood and blood vessels
In other words, it is defined as the stopping of bleeding (aka– blood coagulation)
It involves several complex pathways, platelets, and coagulation factors
Alterations in any of these can cause a bleeding disorder
The primary elements of hemostasis is
Endothelial cells that line the walls of blood vessels
In health, they have anticoagulant properties
Platelets
Coagulation/clotting factors
They are found in the plasma in small concentrations
What are the two parts to the coagualtion process
Chemical and mechanical
What is the mechanical process of caogulation
Initiated when there is a tear or damage to a blood vessel wall
The exposed subendothelium is a charged surface which attracts platelets
von Willebrand factor is required for platelet adhesion, it stabilizes the platelet plug
The adhesion causes platelets to release factors that initiate the chemical phase of blood coagulation
What is the chemical process for coagulation
The chemical phase is known as the coagulation cascade
Remember that the pathways of coagulation are interrelated, interdependent and at least partially cell-based
Each step of the coagulation cascade is dependent on the activation of the clotting factors in the previous steps
What is the coagulation cascade
There are 12 different coagulation factors (Factors I to XIII, there is no Factor XI)
Table 14-1 page 87
Each step triggers the next reaction in the pathway
The end result is a mesh of cross linked, insoluble, fibrin strands that form the blood clot
The final phase of hemostasis is the degradation of the fibrin clot
What are cascade cofactors for coagualtion
The entire clotting process requires many cofactors including Vitamin K and calcium
There are multiple feedback loops
These loops accelerate the process when needed and inhibit the process when necessary
What are the three sections of the coagulation cascade
The coagulation cascade is divided into three pathways, although the sections work together – the divisions are artificial
Intrinsic pathway – intravascular
Extrinsic pathway – within the tissue, helps to initiate the intrinsic pathway
Common pathway – is where the two systems meet
Blood hemostasis is useful for
The coagulation cascade is divided into three pathways, although the sections work together – the divisions are artificial
The absence of a single factor in any of the three sections will result in coagulation deficiencies
We use these systems to help diagnose and pinpoint the coagulopathy
Primary clot factor is and for what
An injured blood vessel will constrict almost immediately
If the defect is small enough, blood flow is stopped
Damage to the vessel wall exposes collagen which triggers platelets to adhere to and aggregate to it
The platelet-collagen complex releases several chemical messengers (coagulation factors) as well as provides a cellular matrix for the main clot to adhere to
What do activated platelets do
Release granules that recruit other platelets to the site
Triggers the coagulation cascade and forms the primary clot
What is secondary clot formation and how does it happen
This is the process of stabilizing the primary clot or platelet plug
Fibrin adheres to the platelets and holds them together like a net
The adherence of fibrin strands is the result of numerous coagulation factors
Both primary and secondary clot formation occur simultaneously
How does a blood clot degrade
Tissue plasminogen activator (tPA) and plasmin:
Break down soluble fibrin into fibrin degradation products (FDPs)
Break down insoluble fibrin into cross-linked FDPs and D-dimers
Why is the degradation of the blood clot important
As important as it is for blood clots to form when vascular damage occurs, it is also important that the body has a mechanism in which to break down blood clots, and inhibit unnecessary clot formation
A series of reactions perform these functions
How to collect the sample for coagualtion tests
When collecting samples for coagulation testing, the sample must be collected quickly and with as little tissue damage as possible
What should you do with a patient that you need a sample from for coagulation tests
Reduce patient excitement as it can cause artificial increases of:
Platelet counts and activation of platelets
Von Willebrand factor
Factors I, V and VIII
What tools should you use to collect blood for a coagulation test
Never collect samples for testing for coagulopathies from an indwelling catheter
Small amounts of fibrin, fibrinogen and platelets are usually present within catheters
If possible, use a vacutainer when collecting the sample
Helps eliminate or reduce platelet activation
Preferred anticoagulant is sodium citrate
When doing platelet counts with this sample you must remember the 10% dilution factor and correct your count
When would you use each coloured blood tube
For platelet counts EDTA it the preferred anticoagulant
Sodium citrate anticoagulant is also used for blood transfusions
When performing whole blood clotting time and activated coagulation time, no anticoagulant is used
When required, sodium citrate tubes are the first anticoagulant tubes to be filled
What is the appropriate amount of sodium to whole blood
Proper fill ratio is one part sodium citrate to nine parts whole blood
Ratio is based on plasma volume
What is unique with clotting time and anemic patients
Anemic patients will have shortened clotting times
Increased plasma volume compared to a non-anemic patient, therefore sample will be “under-citrated”
What is unique in clotting time for dehydrated patients
Polycythemic and dehydrated patients will have prolonged clotting times
Decreased plasma volume compared to a normal patient, therefore sample will be “over-citrated”
What to do after a sample is collected for a coagulation test
The tests should be run within 2 hours of sample collection
Keep the tube upright, tightly sealed and at room temperature
Avoid vibrations
What should you do for a coagulation sample that needs shipping
Centrifuge at 2500 g for 15 minutes (or whole blood setting)
Withdraw plasma without disturbing the platelet layer
Put in a plastic tube and freeze
Ship on dry ice
What is commonly used to perform a coagulation test
Automated machines are preferred over manual methods
They test for specific parts of the coagulation process
Platelet function
Some analyze multiple chemical components
Liquid reagents are used to reverse the action of the anticoagulant
The analyzer then monitors the sample for clot formation
