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Neurology- Clinical > Raised ICP > Flashcards

Raised ICP Flashcards

1
Q

What causes raised ICP?

A

An uncompensated increase in any of the three components of intracranial volume

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2
Q

What is brain compliance?

A

The ability of the brain to tolerate additional intracranial volumes without significantly raising ICP

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3
Q

What occurs once brain compliance has been exhausted?

A

Raised ICP

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4
Q

Which out of the three components of intracranial volume is the one that is the key component of compliance?

A

CSF

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5
Q

How does brain compliance work?

A

Intracranial CSF is squeezed out into the lumbar cistern to decrease the CSF volume

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6
Q

What happens once the maximum volume of CSF that can be expelled has been removed?

A

ICP starts to increase exponentially

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7
Q

What are some causes of raised ICP due to an increase in brain volume?

A

Tumours, infection, cerebral oedema

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8
Q

What are some causes of raised ICP due to an increase in cerebral blood flow?

A

Intracranial haemorrhage or an obstruction to venous outflow

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9
Q

What are some causes of raised ICP due to an increase in CSF?

A

Hydrocephalus, increased CSF production, impaired CSF drainage, idiopathic intracranial hypertension

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10
Q

Normal ICP is identified on imaging by what?

A

No midline shift, normal CSF spaces and normal differentiation between grey and white matter

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11
Q

Do older patients have more or less buffering capacity when it comes to increases in ICP?

A

More

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12
Q

Why are older patients more compliant to small increases in ICP?

A

During ageing, the brain shrinks so the brain volume decreases and more space filled with CSF becomes available inside the skull

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13
Q

What are the 4 classic features of raised ICP?

A

Headache, nausea/vomiting, altered consciousness, papilloedema

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14
Q

What causes Cushing’s reflex to occur?

A

Compression of the cardiorespiratory centres in the medulla

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15
Q

What are the 3 features of Cushing’s triad?

A

Hypertension, bradycardia and abnormal respirations

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16
Q

What does the presence of Cushing’s triad indicate?

A

Severely increased ICP, tonsillar herniation and an immediate risk of cardiorespiratory arrest

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17
Q

Acutely raised ICP may present as what?

A

Brain herniation

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18
Q

What is the safest first investigation for individuals presenting with features of raised ICP?

A

CT brain

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19
Q

What are some features of raised ICP that may be seen on imaging?

A

Midline shift, loss of normal CSF spaces, change in ventricle size, loss of differentiation between grey and white matter

20
Q

What is the purpose of the initial CT scan of someone presenting with features of raised ICP?

A

To rule out a space occupying lesion

21
Q

Why could ventricles be large on a CT scan of someone with raised ICP?

A

Hydrocephalus

22
Q

Why could ventricles be small on a CT scan of someone with raised ICP?

A

Collapsed because of brain swelling

23
Q

What investigation is contra-indicated in any patient with features of raised ICP?

A

Lumbar puncture

24
Q

When can a lumbar puncture be performed on someone with features of raised ICP?

A

Once imaging has excluded a space occupying lesion

25
Q

Why is lumbar puncture contraindicated in patients with raised ICP before a CT scan?

A

It risks cerebral herniation in the presence of a mass lesion

26
Q

In life-threatening raised ICP with signs of brain herniation, what can be done to decrease ICP?

A

Place patient on an artificial ventilator for a short period to decrease CO2 levels

27
Q

Why does artificial ventilation work as a treatment for life-threatening raised ICP with signs of herniation?

A

Causes cerebral blood vessels to constrict which decreases cerebral blood flow, blood volume and hence ICP

28
Q

Why is artificial ventilation only a temporary treatment for life-threatening raised ICP with signs of herniation?

A

It can cause brain ischaemia and infarction if prolonged

29
Q

What are two medications that can be used to reduce ICP before definitive treatment is established?

A

Corticosteroids and mannitol

30
Q

When should corticosteroids be used to reduce ICP and why?

A

In brain tumours as it decreases cerebral oedema

31
Q

How does mannitol reduce ICP?

A

It is an osmotic diuretic which causes absorption of fluid from the CNS and excretes it in the kidneys

32
Q

What is a surgery that can be used in life-threatening cases of raised ICP?

A

Decompressive craniectomy

33
Q

At a fixed blood pressure, increasing ICP will have what effect on cerebral perfusion pressure?

A

It will decrease it

34
Q

What are the normal volumes of ventricular and spinal CSF?

A

30mls each

35
Q

What is the mean CSF pressure?

A

10mmHg/14cmCSF

36
Q

A CSF pressure above what would be considered abnormal?

A

> 15mmHg/20cmCSF

37
Q

CSF is produced at a rate of what?

A

500mls/day

38
Q

Where is the majority of CSF produced?

A

Choroid plexus

39
Q

Describe the Circadian rhythm of CSF production?

A

Maximum at 2am and minimum at 6pm

40
Q

What happens to the production of CSF in the elderly?

A

It decreases

41
Q

What is a drug that reduces the production of CSF by > 50%?

A

Acetazolamide

42
Q

The CSF is absorbed through what? Is this an active or passive process?

A

Arachnoid granulations / passive process

43
Q

Absorption of CSF depends on the ICP being greater than what?

A

Pressure in the sagittal sinus

44
Q

What are the 2 physical functions of CSF?

A

Buoyancy, and accommodates physiological changes in vascular volumes by being displaced into the spinal canal

45
Q

What are the 3 chemical functions of CSF?

A

Provides micronutrients to the brain, clears waste products and is responsible for ionic homeostasis

Neurology- Clinical (31 decks)

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