Cerebral perfusion & ICP Flashcards
How much of the CO does the brain receive?
15%
What is the normal cerebral blood flow?
55 to 60 ml/100g
At what blood flow will ischaemia be observed?
20ml/100g
At what blood flow will permanent brain damage occur?
10ml/100g
What if the effective blood pressure gradient across the brain?
Cerebral perfusion pressure (CPP)
What is the equation which define CPP?
CPP = MAP -ICP
Which an increased ICP what will happen to CPP?
Decrease
What factors regulate cerebral blood flow?
CPP
Arterial O2 & CO2
What is cerebral autoregulation?
The ability to maintain blood flow to the brain over a wide range of CPP (50-150mmHg)
If CPP is low, what will happen to arterioles?
Dilate in order to maintain blood flow
If CPP is high, what will happen to arterioles?
Constrict
What does CO2 do to blood flow?
Cause dilation of vessels do increases
What is a subacute to chronic cause of intracrainal hypertension?
Cerebral oedema
What is the BBB composed of?
Astrocyte foot processes
Endothelial tight junctions
What does the BB prevent?
Prevents toxic materials from reaching brain
What substances are able to cross the BBB?
Lipid soluble substances
According to what doctrine is the skull a rigid structure which contains 3 substances?
Monro-Kelly Doctrine
What 3 substances does the skull contain which contribute to volume?
Brain tissue
Blood
CSF
When there is a new intracranial mass, a compensatory change in volume has to occur which results in____
Decrease in venous blood OR CSF
What is change in compliance?
Change in volume observed for a given change in pressure (dV/dP)
What is elastance?
Change in pressure observed for a given change in volume (dP/dV)
What are the compensatory homeostatic mechanisms the brain compensates for increased ICP?
Veins collapse & squeeze blood out
CSF is displaced from ventricular system to subarachnoid space
At the critical volume, following compensatory homeostatic control, a small change in volume will produce____
large change in pressure
What are the different Lundberg waves =?
ABC waves
What is the Cushings Reflex?
Bradycardia
Hypertension
Irregular breathing
(vasopressor response)
If there is an increase in ICP what will happen to CBF?
Decrease - activation of sympathetic system
What does sympathetic innervation do to CVS?
Vasoconstricts - hypertension
Tachycardia
Why is bradycardia observed in Cushings reflex?
Mechanical distortion of brainstem - respiratory centre crushed.
Aortic baroreceptors stimulate vagus nerve
What is the management for increased ICP?
Raise bed - increase Venous return
Mannitol or hypertonic saline
Hyperventilation: decrease CBF
Surgical decompression
What is the average weight of human brain?
1400g
