Pathophysiology of thrombosis & embolism Flashcards
Normal blood flow is Laminar
What does this mean?
When a fluid flows in parallel layers, with no disruption between the layers
The central layer of fluid moves fastest, with the peripheral layer flowing slowest
With blood in larger vessels, the inner layer is where the cells mainly are, and plasma is on the outside
What determines the velocity of flow of blood?
Pressure gradient
Resistance
Viscosity
Compliance
What are the two big types of abnormal flow?
Stasis - stagnation of blood flow
Turbulence - forceful, unpredictable flow
What medical conditions/things cause abnormal flow?
Thromboembolism Atheroma Hyperviscosity Spasm External compression Vasculitis Vascular steal
What is Virchow’s triad?
3 factors that contribute to thrombosis:
- Changes in vessel walls
- Changes in blood constituents
- Changes in the pattern of blood flow
What actually is thrombosis?
Formation of a solid mass from the constituents of blood within the vascular system during life
Not a clot
Give an example of ‘changes of the vessel wall’
Atheroma
Give examples of ‘changes in the blood constituents’
Hypercholesterolaemia
Thrombophilia or post operative hypercoagulability
Hyperviscosity
Give an example of ‘changes in the blood flow’
Turbulence:
- Atheroma
- Stenosis
- Aortic aneurism
Stasis:
- Post-op
- Being stationary for ages
(overlap between vessel wall changes and blood flow changes)
How would a ruptured plaque cause thrombosis?
Ruptured plaque ∴ exposed collagen & tissue factors
Tissue factors = thrombin formation
Thrombin = fibrin formation
Fibrin meshwork created ∴ platelets adhere to fibrin and thrombus forms
A thrombus has alternating light and dark bands
What are these and what causes them to form?
Lines of Zahn
When thrombus forms:
- Platelets adhere to fibrin creating ‘platelet plaque’
- Platelet plaque traps RBC’s
- Stagnant RBC’s ∴ another plaque forms behind it
- RBC’s trapped behind second plaque
- So on & so on…
Light bands = fibrin & platelet mixture
Dark bands = RBC’s
What determines the consequences of a thrombosis?
Site
Extent
Effects on collateral circulation
What are the main clinical presentations of thrombosis?
Deep vein thrombosis - DVT
Ischaemic limb
Myocardial infarction
What is the worst thing that a thrombus can do…
Embolise
What is embolism?
Movement of abnormal material in the bloodstream and it’s impaction in a vessel, blocking it’s lumen
An embolus is a intravascular detached solid, liquid or gaseous mass
What are the types of embolus?
Systemic/arterial thromboembolus Venous thromboembolus Fat embolism Gas embolism Air embolism Tumour embolism Trophoblast embolism Septic material embolism Amniotic fluid Bone marrow Foreign bodies
What are the sources of a systemic/arterial thromboembolism?
mural thrombus (associated with MI or left atrial dilatation + AF):
- aortic aneurysms
- atheromatous plaques
- valvular vegetations
Mural = endocardial lining or lining of a large BV
What generally happens when a arterial/systemic thrombus embolises?
Travels to wide variety of sites:
Lower limbs, brain, other organs most common
Consequences depend on site & size of thrombus but usually, infarction of the tissue occurs
What is a venous thromboembolus?
Most common form of thromboembolus
Originates in deep veins of the lower limbs - DVT
Usually embolises to pulmonary circulation and may occlude pulmonary artery, the bifurcation or smaller arteries depending on size
What are the possible effects of a venous thromboembolism?
Pulmonary haemorrhage/infarction
Right heart failure
Sudden death
May be silent
Multiple PE over time:
- Pulmonary hypertension
- Right ventricular failure
What medical procedures or conditions increase risk of DVT & pulmonary thromboembolism?
Cardiac failure Severe trauma/burns Post op (+bed rest) Post partum Nephrotic syndrome Disseminated malignancy Obesity Old age
What medication increases risk of DVT & PT?
Oral contraceptives
A surgical patient is identified as high risk for DVT.
What is the next step?
Prophylaxis:
- TEDS
- s/c Heparin
What would cause a fat embolism to occur?
Major fractures
