Thrombosis, embolism & shock Flashcards
Why is clotting a positive?
Normal haemostasis
Maintain blood fluid in normal vessels
Able to induce rapid and localised haemostatic plug at site if vascular injury
What are the 3 steps of normal haemostasis?
Straight after injury - reflex vasoconstriction of arterioles
Endothelium injury exposes highly thrombogenic ECM
Platelets adhere and are activated, leading to the release of chemokines and the recruitment of additional platelets forming a haemostatic plug
How di we limit coagulation
It is important to limit coagulation to site of injury
Anticoagulant mechanisms:
- anti-thrombin
- plasmin activation = breaks down fibrin
Define thrombosis
Inappropriate activation of blood clotting in the vessels leading to a solid/semi-solid mass from the constituents of blood during life
Can form in heart, arteries, veins, capillaries
Arterial - due to injury/foreign material
Venous - at sites of stasis
Define embolism
An embolus is a detached intravascular solid/liquid/gas that is carried by the blood stream to a distant site to its point of origin
Caused by thrombus, fat, tumour, infection, foreign body
What are the 3 factors promoting coagulation
- abnormalities of blood vessel wall due to endothelial injury
- abnormalities of blood flow
- abnormalities of blood’s constituents eg pregnancy, tumours, contraception, trauma
Abnormalities of blood vessel wall and altered blood flow can cause:
myocardial infarction and rheumatoid endocarditis
Abnormalities of blood flow can cause:
Atrial fibrillation and aneurysms
Factors that promote thrombosis
Abnormalities in the vessel wall eg atheroma, inflammation
Abnormalities of blood flow eg. aneurysms, plaques, spasm causing turbulence
Venous thrombosis
Stasis = alters normal laminar flow of blood
Immobility due to loss of function, post-op etc.
Direct compression of veins eg ovarian tumours compressing on pelvic veins
Fate of thrombi
- Resolution - fibrinolysis
- Organisation -
incorporation into a scar by macrophages and fibroblasts
vessel lumen remains narrowed
cell proliferation, capillary invasion & recanalisation, vessel become patent again - Detachment - thromboembolism
Thrombi (emboli)
eg. massive fatal pulmonary thromboembolism lodged in major branch of pulmonary artery
Fat (emboli)
eg. petechial haemorrhage in brain due to fat emboli
Tumour (emboli)
When tumour penetrates blood vessel parts of tumour may break off and metastasise
Atheroma (emboli)
eg. fragments of plaque may break off
What is shock?
when organs and tissues of the body are not receiving an adequate flow of blood, depriving them of oxygen and allows build up of waste products
can cause serious damage and death
Clinical features of shock
low systolic BP (<110) tachycardia (>90bpm) resp rate <7 >29 breaths/min low urine output metabolic acidosis hypoxia anxiety, legarthy
3 stages of shock
- Compensated = non-progressive, blood volume loss 15-25%
- Non-compensated = progressive, blood volume loss over 25%
- Irreversible = failure to restore circulation, critical organ damage
Hypovolaemic shock
internal/external haemorrhage
high output fistulae (intestinal failure)
severe burns
Cardiogenic shock
large acute myocardial infarction/other acute cardiac disease
Septic shock
endotoxins from Gram negative bacteria
exotoxins from gram positive bacteria
shock sequence of dilation of blood vessels
bowel infarction/limb ischaemia
Anaphylactic shock
severe form of allergic reaction to food, antibiotics, insect sting etc.
Neurogenic shock
spinal chord trauma/damage
regional anaesthesia
Obstructive shock
cardiac tamponade
massive pulmonary embolism
tension pheumothorax
