Blood, Anaemia and Haemostasis Flashcards
(33 cards)
What is anaemia?
A Hb level below that which is normal for age and gender
What is the equation for tissue oxygen delivery?
CO x Hb x %saturation of O2 x 1.34
What are the clinical signs of anaemia?
Pale, lethargic, failure to thrive, hypoxic, ischaemia, tachycardia (if sudden onset)
What are the 3 causes of anaemia?
Failure of production
Increased destruction/loss
Inappropriate production
What are the 2 classifications of anaemia?
Regenerative - blood loss or breakdown - bone marrow working normally - Hb goes down quickly Aregenerative - bone marrow isn't making enough cells - Hb goes down slower
How do you determine is a patient needs a transfusion?
- can the patient maintain their HR working at the rate it is until it fails?
- -> need to look at the HR (cardiac compensation)
What do hypochromic RBCs indicate?
Pale cells, no haemoglobin
What do polychromatic RBCs indicate?
Bluish tinge - immature (prematurely released from the bone marrow)
What are the signs of decreased production of red cells?
Reticulocytes and polychromasia
What are the signs of increased destruction of red cells?
Jaundice (increased serum bilirubin), haptoglobins (bind free Hb), LDH (picks up bilirubin)
Where does haemopoiesis occur and when?
At 6 weeks to 7 months made in the liver and spleen
7 months onwards throughout life made in the bone marrow
What is haemostasis?
An interaction of platelets, coagulation factors, coagulation inhibitors, fibrinolytic processes and blood vessels/endothelium
- functions to plug any holes in the system to allow blood to remain in the fluid phase
What is primary haemostasis and the timing of it?
Consists of vasoconstriction, platelet adhesion and platelet aggregation
- timing is immediately - seconds to minutes
What is secondary haemostasis and the timing of it?
Activation of coagulation factors and the formation of fibrin
- timing is minutes
What is fibrinolysis and the timing of it?
Activation of fibrinolysis and the lysis of the clot
- timing is minutes to hours
What is Virchow’s triad?
Hypercoagulability, stasis of blood flow and endothelial injury
- lead to thrombosis
Describe how the vessel wall contributes to haemostasis?
The vessel wall has an endothelial cell surface which interacts with blood and subcutaneous tissue - it can be antithrombotic or prothrombotic depending on expression of surface molecules
How does the process of coagulation start?
Tissue factor is the starter motor –> exposed through endothelial damage, binds to FVII (converted to FVIIa)
- this then activated FX
What are the 3 phases of coagulation?
- Initiation phase
- initiate a clot - Amplification phase
- make the decision to drive amplification - Propagation phase
- extend the clot to cover the entirety of the hole
What is the final step in the coagulation pathway?
Pro-thrombin (II) is converted to thrombin (IIa) via FXa and FVa
Thrombin then converts fibrinogen to fibrin which crosslinks to form a stable fibrin clot (reinforces the platelet plug)
What are the actions of thrombin?
It is a controller - essential to convert fibrinogen to fibrin (insoluble clot)
- on/off switch for haemostasis
- binds to thrombomodulin (reduce coagulation)
- activates platelets
How is thrombin inactivated?
By binding of thrombomodulin
- APC down regulates the ability to cleave fibrinogen (inhibits FVa and FVIIIa)
- increases plasmin formation
How is a clot broken down?
Plasmin activating inhibitor normally inhibits tissue plasminogen (want to keep a clot) but to break it down APC inhibits the plasmin activating inhibitor (so less inhibition of tissue plasminogen) plasminogen –> plasmin –> break down of clot
What is the APTT measuring?
The time until conversion of fibrinogen to fibrin
- intrinsic pathway
