ICP and Cerebral Blood Flow Flashcards
what is found in the intracranial cavity?
nervous tissue, blood vessels, venous channels and CSF and the dynamic balance between these contents creates the ICP
what is the normal ICP?
5-15cm of water
what activities cause transient increase and decrease in ICP?
straining, sneezing or getting up from recumbent position but sustained increase beyond 20cm of water is pathological
what is the Monro-Kellie hypothesis?
intracranial volume is fixed due to non-compliant skull, contents are non-compressible, change in volume of contents or addition of new space occupying lesion increases pressure unless compensated by reduction of other content
what is the pathology of raised ICP?
localised shifts of brain across various compartments which can cause a focal or global reduction of blood flow causing focal or global ischaemia causing reduced energy production causing pump failure on cell membrane causing cellular dysfunction causing membrane damage and cell death
what is mean arterial pressure (MAP)?
diastolic pressure + 1/3 of the pulse pressure (difference between systolic and diastolic) and is the mean pressure in the artery pushing blood towards the brain
what is cerebral perfusion pressure (CPP)?
difference between MAP and ICP- basically the blood being pumped into the brain and the pressure pushing against this
what is cerebro-vascular resistance (CVR)?
resistance offered by cerebral vasculature to flowing blood
what is normal cerebral blood flow?
50ml/100g (of brain)/min or 700ml/min= roughly 14% of cardiac output
what is autoregulation?
ability of brain to maintain constant blood flow over wide range of pressure and ability to increase blood flow to specific regions in brain when these are active eg temporal lobe during speech
what does cerebral blood flow depend on?
the MAP, ICP, vascular resistance and auto regulatory mechanisms of the brain
what are the autoregulation mechanisms?
autonomic neurogenic theory= parasympathetic and sympathetic drives cause vasodilation and vasoconstriction, endothelial mechanisms= cells are sensitive to the pressure of blood inside them, myogenic autoregulation= muscles can stretch in response to to changes in pressure of blood within, metabolic autoregulation= PaCO2 has significant influence on CBF so if low= vasoconstriction and if high= vasodilation, PaO2 only influences if drops significantly
what is the importance of CBF, ICP and autoregulation?
brain tissue uses glucose and ketones exclusively for metabolism, brain tissues have no stored energy source so impaired blood flow will lead to mitochondrial energy production failure within seconds and cell death within minutes and injured brain loses its ability to auto regulate hence hypotension, hypertension, hypoxia or raised iCP which an lead to significant secondary insult
