Lecture 17 - Raised Intracranial Pressure Flashcards
What are the 3 components that contribute to intracranial pressure?
BBC
Brain
Blood
CSF
What is intracranial pressure?
The pressure experience inside the Neurocranium
What is the normal range of intracranial pressure in adults?
5-15mmHg
What is the normal range of intracranial pressure (ICP) in children??
5-7mmHg
What is considered raised ICP?
Anything above 20mmHg
What is the Monro-Kellie Doctrine?
States that any increase in the volume of one of the intracranial constituents must be compensated by a decrease in volume of one of the other intracranial constituents to help prevent the increase in ICP
In the presence of an intracranial mass, what is reduced in volume in an attempt to prevent increased ICP and why?
CSF and venous blood since they are low pressure circulations
Brain is a typically fixed volume
What is the relationship between intracranial pressure and volume?
As intercranial volume increases intracranial pressure remains constant up until a certain point, after this point the pressure begins to increase
Why does intracranial pressure not immediately increase as intracranial volume increases?
Compensatory mechanisms of decreasing CSF and venous blood volume help prevent ICP increasing
Why does intracranial pressure increase as intracranial volume increases after a certain point?
Compensatory mechanisms start to deplete (venous blood and CSF volumes can only be reduced so much)
What are the 3 types of causes of intracranial pressure?
Too much CSF
Too much blood
Too much brain
What is the condition called where theres too much CSF?
Hydrocephalus
What are the 2 categories of hydrocephalus causing ICP?
Congenital
Acquired
What are some causes of congenital hydrocephalus?
Obstructive:
-neural tube defects
-aqueduct stenosis
-part of a larger syndrome
Communicating (drainage not impaired):
-inc CSF production
-dec CSF absorption
What are the clinical sings of hydrocephalus?
Bulging head with head circumference increasing faster than expected
Sunsetting eyes
What causes sunsetting eyes in hydrocephalus?
Direct compression of orbits
Occulomtor nerve involvement as it exits midbrain
Would you expect to see an enlarged skull in an adult patient with hydrocephalus and why?
No since fontanelles and sutures have fully ossified
In young kids fontanelles and sutures haven’t fully ossified so can expand with the growing ICP
How can you see hydrocephalus on an MRI or CT head?
Enlarged ventricles (easy to see lateral ventricles )
What is the most common treatment for hydrocephalus?
Ventricular peritoneal shunting of CSF
Shunt (tube) implanted from ventricles to the peritoneum , one way valve prevents back flow to ventricles
What are some acquired causes of hydrocephalus?
Meningitis (abscesses can compress ventricular drainage)
Trauma
Haemorrhage
Tumours (compress cerebral aqueduct)
What are some causes of too much blood causing inc ICP?
Intracranial haemorrhage
Haemorrhagic stroke
Too much blood in cerebral vessels (rare)
What are some causes of too much blood in cerebral vessels causing raised ICP?
Raised arterial pressure (malignant hypertension)
Raised venous pressure
What can cause raised venous pressure leading to raised ICP?
Superior vena cava obstruction (can happen from compression by a lung tumour)
What are some causes of having “too much brain” leading to raised ICP?
Cerebral oedema
What are the 4 major pathophysiologies for cerebral oedema?
Vasogenic (breakdown of tight junctions)
Cytotoxic (damage to brain cells)
Osmotic (if ECF becomes hypotonic)
Intersitial (flow of CSF across Ependyma and damage to BBB)
What are some other causes of raised ICP? (Not blood, brain or CSF BBC)
Tumour
Cerebral abscess
Idiopathic intracranial hypertension (benign intracranial hypertension)
Describe a characteristic patient with idiopathic intracranial hypertension:
Woman of childbearing age
Overweight
Headaches
Blurring vision
What volume do people with idiopathic intracranial hypertension have increased amount of?
CSF
What are the 2 major consequences of raised ICP?
Brain ischaemia (due to impaired cerebral perfusion since poor arterial blood flow)
Compression and herniation of the brain
What are the main types of herniation?
Subfalcine
Uncal
Central downward herniation through the tentorial notch
What determines cerebral blood flow?
Cerebral perfusion pressure
What determines cerebral perfusion pressures?
Mean arterial pressure
Intracranial pressure
What is the equation for cerebral perfusion pressure?
CPP = Mean arterial pressure - ICP
What is the normal Cerebral Perfusion Pressure?
CPP > 70
What auto regulatory system is important in maintaining CCP and cerbreal blood flow?
Cerebral auto regulation
What is the function of the cerebral auto regulatory mechanism?
Ensures Cerebral Perfusion Pressure and cerebral blood flow can be steadily maintained despite the fluctuations seen in the bodies changes in MAP
What is the auto regulated response to mean arterial pressure dropping in order to prevent the Cerebral Perfusion Pressure from dropping (CPP)?
Cerebral arterioles dilate to help keep the vessels open to maximise blood flow
What is the auto regulated response to mean arterial pressure rising in order to prevent the Cerebral Perfusion Pressure from increasing (CPP)?
Vasoconstriction of cerebral arterioles to reduce blood flow to the cerebral arteries
If the brain tissue is damaged, what effect can this have on maintaining CPP?
Cerebral auto regulation is impaired or absent so without cerbreal auto Regualtion CPP is dependant to on changes to oMAP
What affect does inc ICP have on CPP?
Decreases CPP but mechanisms but in place to mitigate
What is the mechanism which occurs to increased ICP?
Cerebral Arterioles vasodilates to increase blood flow due to cerebral auto regulation
Elevate MAP
What is the problem with elevating MAP as a response to increased ICP to maintain CPP?
Increasing cerebral blood volume will only worsen the increasing intracranial pressure
What are the steps which occur with a tumour causing raised ICP?
CSF and venous blood reduce to help compensate
ICP rises reducing CPP, so brain cerebral vasodilates and MAP increases
ICP raises more and CPP cant compete so brain becomes HYPOXIC
Cerebral hypoxia leads to cerebral oedema which further increases ICP
Compression on brain and brainstem,
Why may you delay doing a lumbar puncture on a patient with meningitis?
If you suspect they have a raised ICP
LP will lead to the pressure suddenly decreasing which can lead to brain herniation
What are some common presenting features of rising ICP at the start?
Headache (worse in morning or coughing)
Vomiting
Visual disturbance
What are some visual disturbances that you can see as ICP starts to rise?
Impaired visual acuity
Papilloedema (pressure on optic nerve)
Diplopia (CN VI)
What are the presenting features of a patient with raised ICP to the point where we start getting cerebral hypoxia?
Difficulty concentrating
Focal neurological signs
Seizures
Inc BP
Reduced GCS:
-confusion
-drowsiness
-unconsciousness
Slide 24:
What are these 3 signs of raised ICP?
CN VI compressed
Papilloedema
CN III (blown pupil)
What are some radiological features of raised ICP?
Subfalcine herniation (midline shift)
Other brain herniation effacement of ventricles
Loss of grey-white matter differentiation
What are the 3 main types of herniation that can occur with increased ICP?
Subfalcine herniation
Uncal/transtentorial herniation
Tonsillar herniation / coning
What is a Subfalcine herniation?
What blood vessel is at risk in this type of herniation?
Cingulate gurus herniates under the falx cerebri
Anterior cerebral artery at risk of occlusion
What is an uncal/transtentorial herniation?
What is at risk?
When the uncus of the temporal lobe herniates under the tentorium cerebelli
Can compress the oculomtor nerve (CN III) and the cerebella’s peduncle
What is a tonsillar herniation/coning?
What is at risk?
Cerebella’s tonsils herniate through Foramen magnum
Can compress the brainstem (will be fatal)
What is Cushing’s triad?
A late feature of raised ICP
Triad of:
-hypertension
-bradycardia
-irregular Breathing
Why do we get Cushing’s triad/reflex with raised ICP?
As ICP increases MAP increases to help maintain Cerebral perfusion pressure (HYPERTENSION)
Since MAP increases the Baroreceptors detect this an trigger BRADYCARDIA via vagal activity
The continued pressure on the brainstem compresses cardio-respiratory centres in the medulla leading to irregular breathing
How do you manage a patient with acutely raised ICP?
ABC
Resuscitate and stabilise maintaining Airways and breathing, then ensure MAP and CPP are maintained
Sedate and analgesia
Head up tilt about 15 degrees improving venous drainage
When trying to protect brain in a patient with raised ICP we want to avoid hypotension, if a patient has hypertension why may. We be reluctant to do something to reduce it?
The raised MAP might be driving blood supply to the brain
What is a side effect of increased vagal tone from the Cushing’s reflex with raised ICP?
Stomach ulcers
What are some drugs that may given to a patient with raised iCP?
Osmotherpaies like mannitol
PPI to prevent stomach ulcers (due to inc vagal activity)
Anticonvulsants
Antipyretics
What are some non drug treatments for an acute raised ICP?
Last. Resort decompresive craniectomy
Ventricular drainage
Bolt to invasivley measure ICP
What values do we want to maintain ICP in for an patient with raised ICP?
Less than 20-25. MmHg
