Flashcards in L14- Ischaemia, Infarction & Shock Deck (33):
What is Hypoxia
Any state of reduced tissue oxygen availability
-Generalised - whole body e.g. altitude, anaemia
-Regional - specific tissues affected
What is Ischaemia
Pathological reduction in blood flow to tissues
-Usually as a result of obstruction to arterial flow
-commonly as a result of thrombosis / embolism
-Ischaemia results in tissue hypoxia
How harmful is ischaemia? (Limited vs prolonged duration)
If limited / short duration ---> cell injury reversible
Prolonged / sustained ---> irreversible cell damage
Cell death occurs by necrosis (infarction)
Why can reperfusion of non-infarcted but ischaemic tissue be bad?
Whats is Infarction
Ischaemic necrosis caused by occlusion of the arterial supply or venous drainage
Other causes of infarction?
Vasospasm (sudden blood vessel contraction)
Extrinsic compression (e.g. tumour)
Twisting of vessel roots (e.g. volvulus)
Rupture of vascular supply (e.g. AAA)
Morphology of infarction : Red infarct vs White
Red infarction (haemorrhagic)
Dual blood supply / venous infarction
White infarction (anaemic)
Single blood supply hence totally cut-off
Why are most infarcts wedge shaped?
Obstruction usually occurs at an upstream point
The entire down-stream area will therefore be infarcted
What are the histological characteristics of infarcts
Coagulative necrosis (usually)
Colliquative necrosis (in the brain)
If a person dies suddenly (e.g. massive heart attack) what do you see in the tissues?
No time to develop haemorrhage / inflammatory response
What factors influence the degree of ischaemic damage?
Nature of the blood supply (e.g is there a collateral supply present?)
Rate of occlusion (slow forming ones are less likely to infarct tissues)
Tissue vulnerability to hypoxia (The brain is vulnerable/ the heart is a bit more resistant)
Blood oxygen content (Reduced oxygen in the blood (anaemia etc.) increases the chances of infarction)
Clinical Manifestations of Ischaemia?
Ischaemic heart disease (angina / MI)
Cerebrovascular disease (TIA / CVA)
Peripheral vascular disease / gangrene
(Remember THE 5 Ps as well)
What is Cerebrovascular disease
Any abnormality of the brain caused by a pathological process involving the blood vessels
-Thrombosis and embolism (ischaemic)
What is a Cerebrovascular accident
Causes of an ischaemic stroke:
-Thrombosis secondary to atherosclerosis
-Embolism (e.g. mural thrombus)
What are the causes of a haemorrhagic stroke
Intracerebral haemorrhage (hypertensive)
Ruptured aneurysm in the circle of Willis (subarachnoid)
What is Ischaemic bowel disease
Usually caused by thrombosis or embolism in the superior or inferior mesenteric arteries
Presents with abdominal pain
Limb ischaemia / infarction presentation
Infarction of entire portion of limb (or organ)
Ischaemic coagulative necrosis only
Superimposed infection with gas producing organism e.g. clostridium perfringens
What is Shock
A physiological state characterised by a significant reduction of systemic tissue perfusion (severe hypotension)
Which results in decreased oxygen delivery to the tissues.
What can impaired tissue perfusion and oxygen deprivation lead to?
cellular hypoxia and derangement of critical biochemical processes at first cellular and eventually systemic levels.
Cellular effects of shock...
Membrane ion pump dysfunction
Leakage of intracellular contents into the extracellular space
Inadequate regulation of intracellular pH
Anerobic respiration ---> build up of lactic acid
Systemic effects of shock...
Alterations in the serum pH (acidaemia)
Endothelial dysfunction ---> vascular leakage
Stimulation of inflammatory and anti-inflammatory cascades
End-organ damage (ischaemia)
Is shock reversible?
Initially it is, but then becomes irreversible as:
-Cells start to die
-End organs are damaged
-Organs begin to fail
---> eventually leading to DEATH
Types of shock
(severe blood and fluid loss)
(heart suddenly can't pump enough blood to meet your body's needs)
(Anaphylactic, septic, toxic shock syndrome, neurogenic)
What is Hypovolaemic shock
Intra-vascular fluid loss (blood, plasma etc)
↓ venous return to heart AKA “pre-load”
↓ stroke volume ---> ↓ cardiac output
What is the body's response to Hypovolaemic shock?
Systemic vascular Resistance
What are the causes of Hypovolaemic shock?
-Trauma, gastrointestinal bleeding, ruptured haematoma , aneurysm
Non-haemorrhagic fluid loss:
-Diarrhoea, vomitting, heat stroke, burns
What is Cardiogenic shock ?
Cardiac pump failure
The 4 categories of Causes of Cardiogenic shock?
Myopathic (heart muscle failure e.g after M.I)
Arrythmia-related (abnormal electrical activity e.g AF)
Mechanical (problems with the valves)
Extra-cardiac (obstruction to blood outflow e.g PE, Anything that impairs cardiac filling or ejection of blood from heart)
What is third spacing?
Acute loss of fluid into internal body cavities
Types of Distributive shock: What is Septic shock and what happens during it
Severe, over-whelming systemic infections with Gram+ve, gram-ve bacteria or fungi
Inc in Cytokines / mediators ---> VASODILATION
Pro-coagulation (DIC) ---> Ischaemia
Types of Distributive shock: What is Anaphylactic shock and what can cause it?
Severe type I hypersensitivity reaction
Hospital e.g. drugs (penicillin etc)
Community e.g. peanuts, shellfish, or insect toxins
Small doses of allergen ---> IgE cross-linking (stimulates mast cells) ---> Vasodilation
Contraction of bronchioles / respiratory distress
Circulatory collapse ---> shock / death
Types of Distributive shock: What is Neurogenic shock
Spinal injury / anesthetic accidents
Loss of sympathetic vascular tone
Vasodilation ---> shock