Lect 14 - Ischaemia, Infarction & Shock Flashcards
What is hypoxia?
Any state of reduced tissue oxygen availability
this can be generalised - whole body e.g. altitude, anaemia
or 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
what is infarction
Ischaemic necrosis caused by occlusion of the arterial supply or venous drainage
Give some causes of infarction that are not caused by blood clots
Vasospam Atheroma expansion Extrinsic compression (e.g. tumour) Twisting of vessel roots (e.g. volvulus) Rupture of vascular supply (e.g. AAA)
what are the types of infaction?
Red infarction (haemorrhagic) White infarction (anaemic)
what shape are infarcts?
Most infarcts are wedge-shaped
Obstruction usually occurs at an upstream point, everything downstream is affected.
what would you expect to see histologically in infarction?
Coagulative necrosis (Colliquative) in the brain
what 4 factors influence the degree of ischaemic damage
Nature of the blood supply
Rate of occlusion
Tissue vulnerability to hypoxia
Blood oxygen content
give examples of areas which are less prone to ischaemic damage due to nature of blood supply
Lungs (pulmonary and bronchial arteries)
Liver (hepatic artery and portal vein)
Hand (radial and ulnar artery)
why does a quick rate of occlusion make ischaemic damage worse?
doesn’t allow time for the development of alternative (collateral) perfusion pathways
what tissues are the most vulnerable to lack of oxygen?
The brain
(irreversible cell damage in 3 to 4 minutes)
The heart
(Mycocyte death in 20 to 30 minutes)
what is the leading cause of death in men and women in the West
Ischaemic heart disease
give 2 causes of ischaemic stroke
Thrombosis secondary to atherosclerosis
Embolism (e.g. mural thrombus)
give 2 Causes of a haemorrhagic stroke
Intracerebral haemorrhage (hypertensive)
Ruptured aneurysm in the circle of Willis (subarachnoid
What disease presents with abdominal pain and is caused by the same pathological process as Ischaemic heart disease
Ischaemic bowel disease
what does limb ischaemia lead to?
Gangrene
what types of Gangrene are there?
Dry gangrene (Ischaemic coagulative necrosis only)
Wet gangrene (Superimposed infection)
Gas gangrene (Superimposed infection with gas producing organism)
define gangrene
Infarction of entire portion of limb (or organ)
define shock
A physiological state characterised by a significant reduction of systemic tissue perfusion (severe hypotension) resulting in decreased oxygen delivery to the tissues.
what does shock lead to?
cellular hypoxia and derangement of critical biochemical processes at first cellular and eventually systemic levels.
give some Cellular effects of shock (5)
Membrane ion pump dysfunction Intracellular swelling Leakage of intracellular contents into the extracellular space Inadequate regulation of intracellular pH Anerobic respiration ( makes lactic acid)
give some Systemic effects of shock (4)
acidaemia
vascular leakage
Stimulation of inflammatory and anti-inflammatory cascades
End-organ damage
after shock becomes irreversible, what sequence of events leads to death?
Cell death
End-organ damage
Multi-organ failure
Death
what is Hypovolaemic shock?
Intra-vascular fluid loss.
less preload therefore less cardiac output.
what Causes hypovolaemic shock
Haemorrhage, Diarrhoea, vomiting, heat stroke, burns
what is Cardiogenic shock
Cardiac pump failure
what are the Categories of cardiogenic shock
Myopathic (heart muscle failure)
Arrythmia-related (abnormal electrical activity)
Mechanical
Extra-cardiac (obstruction to blood outflow)
what are the casues of myopathic cardiogenic shock
Myocardial infarction
Right ventricular infarction
Stunned myocardium (following prolonged ischemia)
what arrhythmias cause cardiogenic shock
Atrial and ventricular arrhythmias (fibrillation / flutter )
also Ventricular tachycardia, bradyarrhythmias, and complete heart block
give some causes of Extra-cardiac cardiogenic shock
Anything that impairs cardiac filling or ejection of blood from heart
Massive pulmonary embolism
tension pneumothorax
Severe constrictive pericarditis
pericardial tamponade
what is Distributive shock?
severe vasodilation that massively lowers systemic vascular resistance.
what sub types of Distributive shock are there?
SEPTIC SHOCK
ANAPHYLACTIC SHOCK
NEUROGENIC SHOCK
TOXIC SHOCK SYNDROME
what is Septic Shock?
Severe, over-whelming systemic infections.
Cytokines and mediators casue the VASODILATION
DIC can also cause Ischaemia
what is Anaphylactic shock
Severe type I hypersensitivity reaction:
Massive mast cell degranulation casues Vasodilation and also respiratory distress. Patients undergo Circulatory collapse.
what is Neurogenic shock?
Spinal injury / anesthetic accidents
Loss of sympathetic vascular tone leads to Vasodilation
what is Toxic shock syndrome?
S. aureus /S. pyogenes produce exotoxins known as “superantigens” that Do not require processing by antigen-presenting cells.
this casues Non-specific binding of class II MHC to T cell receptors - Widespread release of massive amounts of cytokines
are there combined types of shock?
Yes. like septic shock with a Primary distributive component/Hypovolemic component/ Cardiogenic component
the infection can lead to symptoms which then compound the shock (like diarrhoea)
what is the mortality of Cardiogenic shock?
60 – 90% mortality
