Intracrainal pressure and cerbral perfusion Flashcards
What is normal ICP?
5 to 15 cm of water
What are some factors that change ICP?
Sneezing, straining, and getting up from a recumbent position
What is the Monro-Kellie hypothesis?
That the intracranial volume is fixed due to the non-compliant nature of the skull and that the contents are non-compressible, thus any change in volume or addition of new space-occupying lesion increases pressure by reduction of other contents.
How does the intracranial content compensate due to a large extradural hematoma?
Reduction in venous blood in brain, displacement of CSF towards the spine, reduction of CSF volume.
What are the effects of raised ICP?
Brain shifts across various components, reduction in blood flow, reduced energy production of the brain, failure of the pump to work on the cell membrane, ischemia, toxic metabolite increase, cell death.
What are ways to measure ICP?
Epidural bolt, EVD - external venous drainage, subarachnoid bolt.
Why are there waves in the CSF pressure?
Due to the flow of blood affecting CSF production.
What is the cause of the P1 wave?
Percussion wave, correlates with the arterial pulse transmitted through the choroid plexus into the CSF, and via a column of fluid into the EVD transducer. It will lag slightly behind the arterial transducer.
What is the cause of the P2 wave?
Also known as the tidal wave, represents cerebral compliance, it can be thought of as a ‘reflection’ of the arterial pulse wave bouncing off the springy brain parenchyma.
What is the cause of the P3 wave?
Also known as the dicrotic wave, correlates with the closure of the aortic valve, which makes the trough prior to P3 the equivalent of the dicrotic notch.
What is cerebral perfusion pressure?
Difference between mean arterial pressure and ICP.
What is MAP made up of?
Diastolic plus 1/3 of pulse pressure.
What is cerebrovascular resistance?
Resistance due to cerebral vasculature to flowing blood.
What factors affect cerebral blood flow?
Mean arterial pressure, intracranial pressure, vascular resistance, auto-regulation of the brain.
What is the effect of auto-regulation on the brain?
It increases blood flow to certain areas of the brain depending on how much they are being used, such as to speech area during speech.
What are the ways the brain auto-regulates itself?
Autonomic neurogenic theory, endothelial mechanisms, myogenic autoregulation, metabolic autoregulation.
What is the autonomic neurogenic theory?
Uses vasodilation and vasoconstriction to control the brain pressure.
What is the endothelial vasodilation measure?
Endothelial cells secrete vasodilating substances to constrict or dilate the blood vessels.
What is the myogenic autoregulation theory?
Where due to a change in blood pressure, blood vessels contract or expand accordingly.
What is the metabolic autoregulation theory?
That PaCO2 has a high influence on CBF, and when it drops it insignificantly influences it, and that PaO2 only influences CBF slightly.
Does brain tissue have an alternative source apart from glucose and ketones?
No.
How quickly does mitochondria fail in the brain?
Seconds.
How long does it take for cells to die in the brain?
Minutes.
What are the effects of head injury on intracranial pressure?
Raised.
What is the effect on lungs and heart as a result of head injury?
Hypoxia and hypotension.
What is the benefit of neuromonitoring of ICP?
It allows the option of CPP to prevent brain insult by reducing high ICP and preserving low or high CPP.
Why does raised ICP lead to a headache?
Puts pressure onto the brain, leading to loss of blood and cause of neuroprotection damage.
What is the body pathophysiological response to increased brain pressure?
Widened pulse pressure, bradycardia, irregular respiration.
What is Cushing’s response?
The pathophysiological response to raised ICP.