Raised ICP Flashcards
What causes raised ICP?
An uncompensated increase in any of the three components of intracranial volume
What is brain compliance?
The ability of the brain to tolerate additional intracranial volumes without significantly raising ICP
What occurs once brain compliance has been exhausted?
Raised ICP
Which out of the three components of intracranial volume is the one that is the key component of compliance?
CSF
How does brain compliance work?
Intracranial CSF is squeezed out into the lumbar cistern to decrease the CSF volume
What happens once the maximum volume of CSF that can be expelled has been removed?
ICP starts to increase exponentially
What are some causes of raised ICP due to an increase in brain volume?
Tumours, infection, cerebral oedema
What are some causes of raised ICP due to an increase in cerebral blood flow?
Intracranial haemorrhage or an obstruction to venous outflow
What are some causes of raised ICP due to an increase in CSF?
Hydrocephalus, increased CSF production, impaired CSF drainage, idiopathic intracranial hypertension
Normal ICP is identified on imaging by what?
No midline shift, normal CSF spaces and normal differentiation between grey and white matter
Do older patients have more or less buffering capacity when it comes to increases in ICP?
More
Why are older patients more compliant to small increases in ICP?
During ageing, the brain shrinks so the brain volume decreases and more space filled with CSF becomes available inside the skull
What are the 4 classic features of raised ICP?
Headache, nausea/vomiting, altered consciousness, papilloedema
What causes Cushing’s reflex to occur?
Compression of the cardiorespiratory centres in the medulla
What are the 3 features of Cushing’s triad?
Hypertension, bradycardia and abnormal respirations
What does the presence of Cushing’s triad indicate?
Severely increased ICP, tonsillar herniation and an immediate risk of cardiorespiratory arrest
Acutely raised ICP may present as what?
Brain herniation
What is the safest first investigation for individuals presenting with features of raised ICP?
CT brain
What are some features of raised ICP that may be seen on imaging?
Midline shift, loss of normal CSF spaces, change in ventricle size, loss of differentiation between grey and white matter
What is the purpose of the initial CT scan of someone presenting with features of raised ICP?
To rule out a space occupying lesion
Why could ventricles be large on a CT scan of someone with raised ICP?
Hydrocephalus
Why could ventricles be small on a CT scan of someone with raised ICP?
Collapsed because of brain swelling
What investigation is contra-indicated in any patient with features of raised ICP?
Lumbar puncture
When can a lumbar puncture be performed on someone with features of raised ICP?
Once imaging has excluded a space occupying lesion
Why is lumbar puncture contraindicated in patients with raised ICP before a CT scan?
It risks cerebral herniation in the presence of a mass lesion
In life-threatening raised ICP with signs of brain herniation, what can be done to decrease ICP?
Place patient on an artificial ventilator for a short period to decrease CO2 levels
Why does artificial ventilation work as a treatment for life-threatening raised ICP with signs of herniation?
Causes cerebral blood vessels to constrict which decreases cerebral blood flow, blood volume and hence ICP
Why is artificial ventilation only a temporary treatment for life-threatening raised ICP with signs of herniation?
It can cause brain ischaemia and infarction if prolonged
What are two medications that can be used to reduce ICP before definitive treatment is established?
Corticosteroids and mannitol
When should corticosteroids be used to reduce ICP and why?
In brain tumours as it decreases cerebral oedema
How does mannitol reduce ICP?
It is an osmotic diuretic which causes absorption of fluid from the CNS and excretes it in the kidneys
What is a surgery that can be used in life-threatening cases of raised ICP?
Decompressive craniectomy
At a fixed blood pressure, increasing ICP will have what effect on cerebral perfusion pressure?
It will decrease it
What are the normal volumes of ventricular and spinal CSF?
30mls each
What is the mean CSF pressure?
10mmHg/14cmCSF
A CSF pressure above what would be considered abnormal?
> 15mmHg/20cmCSF
CSF is produced at a rate of what?
500mls/day
Where is the majority of CSF produced?
Choroid plexus
Describe the Circadian rhythm of CSF production?
Maximum at 2am and minimum at 6pm
What happens to the production of CSF in the elderly?
It decreases
What is a drug that reduces the production of CSF by > 50%?
Acetazolamide
The CSF is absorbed through what? Is this an active or passive process?
Arachnoid granulations / passive process
Absorption of CSF depends on the ICP being greater than what?
Pressure in the sagittal sinus
What are the 2 physical functions of CSF?
Buoyancy, and accommodates physiological changes in vascular volumes by being displaced into the spinal canal
What are the 3 chemical functions of CSF?
Provides micronutrients to the brain, clears waste products and is responsible for ionic homeostasis
