S5) Thrombosis and Embolism Flashcards
What is a thrombosis?
A thrombosis is the formation of a solid mass from the constituents of the blood, within the circulatory system
There are three fundamental predisposing factors to thrombosis.
What is this called?
Virchow’s triad
- Changes in the vascuar wall
- changes in blood flow
- Changes in Blood
Identify the three predisposing factors to thrombosis as outlined in Virchow’s triad
- Abnormalities of the flow of blood
- Abnormalities of the blood vessel wall
- Abnormalities of the constituents of the blood
2/3 are enough to create a thrombus
State two possible abnormalities in the flow of blood
- Stagnation
- Turbulence
State three causes for abnormalities in the blood vessel wall
- Atheroma
- Direct injury
- Inflammation
State three causes for abnormalities in the constituents of the blood
- Smoking
- Post-partum
- Post-operation
Describe the appearance of arterial thrombi
- Pale
- Granular
- Lines of Zahn
- Lower cell content
Describe the appearance of venous thrombi
(normally found where there is stasis - slowinf/stopping of blood flow)
- Soft
- Gelatinous
- Deep red
- Higher cell content
What are the 5 possible outcomes of a thrombosis?
- Lysis - thromus dissolves
- Propagation - thrombus grows
- Organisation - undergoes fibrous repair and forms a scar
- Re-canalisation - new channels grow and restore blood flow
- Embolism - part breaks off and embolises
In three steps, describe the following outcome of a thrombosis: lysis
⇒ Complete dissolution of thrombus (small)
⇒ Fibrinolytic system active
⇒ Blood flow re-established
In three steps, describe the following outcome of a thrombosis: propagation
⇒ Progressive spread of thrombosis
⇒ Spreads distally in arteries
⇒ Spreads proximally in veins
In two steps, describe the following outcome of a thrombosis: organisation
⇒ Ingrowth of fibroblasts and capillaries (similar to granulation tissue)
⇒ Lumen remains obstructed
In two steps, describe the following outcome of a thrombosis: re-canalisation
⇒ Blood flow re-established but usually incompletely
⇒ 1/more channels formed through organising thrombus
In three steps, describe the following outcome of a thrombosis: embolism
⇒ Part of thrombus breaks off
⇒ Travels through bloodstream
⇒ Lodges at distant site
What are the arterial effects of thrombosis?
Depends on site and collateral circulation:
- Ischaemia
- Infarction
What are the venous effects of thrombosis?
- Congestion
- Oedema
- Ischaemia
- Infarction
What is an embolism?
An embolism is the sudden blockage of a blood vessel by thrombus or foreign material which has been brough back to its site of lodgement by blood current
(part of a thrombus thats come off)
What is the most common type of embolism?
Over 90% of emboli are thrombo-emboli
What are other types of embolism?
- Air
- Amniotic fluid
- Nitrogen
- Medical equipment
- Tumour cells
Outline the four different pathways for thromboemboli
- From systemic veins → lungs (pulmonary emboli)
- From the heart (via aorta) → renal, mesenteric and other arteries
- From atheromatous carotid arteries → brain
- From atheromatous abdominal aorta → leg arteries
Identify common areas where emboli can occur
- Pulmonary embolism
- Coronary embolism
- Cerebral embolism
What is a deep vein thrombosis?
- A deep vein thrombosis is the formation of a thrombus within a deep vein, most commonly the deep calf veins
- It produces an inflammatory response (calor, dolor, rubor, tumor, functio laesa)
Identify 5 predisposing factors to deep vein thrombosis
- Immobility
- Post-operative
- Pregnancy and postpartum
- Oral contraceptives
- Severe burns
How does one prevent DVT?
- Prophylaxis for high-risk patients
- Heparin sub-cutaneously
- Leg compression during surgery
I. TED stockings
II. ‘Flowtron’ boots
What is the treatment for DVT?
- aspirin
- Intravenous heparin
- Oral warfarin
What is a pulmonary embolism?
- A pulmonary embolism is a sudden blockage of a pulmonary artery in the lung, usually due to a deep vein thrombosis
- It presents with chest pain, shortness of breath, coughing and blood stained sputum
Identify and describe the three forms of pulmonary embolism
- Massive PE – >60% reduction in blood flow (rapidly fatal)
- Major PE – medium-sized pulmonary vessels blocked (SOB ± cough, blood stained sputum)
- Minor PE – small peripheral pulmonary arteries blocked (asymptomatic/SOB)
What is the effect of recurrent minor pulmonary emboli?
Recurrent minor PEs lead to pulmonary hypertension
arterial and cardiac thrombi
occur at site of endothelial injury or turbulence
endothelial damage
- after MI secondary to haemodynamic stress of hypertension, scarred heart valves, after trauma or surgery
- stasis thrombus will form (as platelets, clotting factors and chemical mediators) arent being washed away
Slow/Turbulent flow
abnormal flow increases chance of clot forming
==> Veins have higher chance as their flow is slow
==> Patients on bed rest are at risk
==> occurs in ulcerated atheroscletoric plaques, with aneurysms
turbulent flow can also additionally cause damage to endothelial wall
turbulent flow (calcification/plaque)
formation of a thrombus
- platlets concentrated in th endothelium
- catch onto a valve
- form and aggrevate into a clump
- more platelets join
haemostasis fibrinogen
- Platelets combine
- fibrin gows out
- fibrin traps red blood cells
- then a second layer of white platelets join (lines of zahn)
hypercoagulability
pregnancy/after surgery = increased levels of fibrinogen and factor VIII = blood is hypercoagulability
=->the pill causes this
==> DIC
difference btetween post/pre mortem
post = more rubbery and shiny
thrombophlebitis
painful/superficial thrombi where the vein is inflammed
parietal
thrombi attached to the vessel wall and restrict the the lumen
eg. arterial thrombi
clinical effects of thrombosis
==> occulusion of an artery at site of thrombus
==> embolisation thrombus = occlusion of artery
==> congestion and odema in venous bed
==> repeated miscarriages due to thrombosis of uteroplacental vasculature
thromboemboli
emboli that arise from thrombi
why cant embolization occur in veins
vein blood flows from small -> Large vessels
objects carried by blood in veins goes through right side of heart and embolise in pulmonary arteries
embolization in arteries
blood flows from large - small
objects in the large arteries impact small ones
- arise in the left heart, aneurysms and thrombi and embolise to lower extremities, brain, intestines
paradoxial emboli
RARE!
form in systemic veins but embolise to systemic arteries and bypass lungs
thrombi seen in left heart as
1) infarcts
2) Atrial fibrillation => decreased atrial contraction => dialation of left atrium
3) vegetations
Emboli from Atheroma
- build up of materials that adhere to arteries
occurs spontaneously / surgery / catherisation
TIAs
Transient ischameic attacks
- episodes of neurological dysfunction
- result of microscopic emboli
fat and bone marrow
- complication of bone fractures
- damaged bone marrow fat cells release oil droplets
- sucked up into venules
RESPIRATORY SYMPTOMS
- emboli lodge into lungs
- some droplets pass through into brain, kidney, skin ===> coma, agitation, rash
Gas emboli
negative pressure in veins
air transports into right heart
bubbles gather = frothy mass that stops circulation
fatal = 100mls of air
The bends
- diver resurfaces too quickly then sudden depressurisation => dissolved gases being released as bubbles
bubbles distort tissue and acts as an emboli
- Nitrogen is very bad => fat soluble and creates problems in lipid - rich tissues
treatment
slow decompression
amniotic fluid embolism
complication of labour and C section
amniotic fkuid enters maternal circulation
respiratory distress/hypotension/seizures
Talcum Emboli
microscopic foreign bodies
