Pathophysiology Of Raised Intracranial Pressure

Question 1

Intracranial pressure range in adults

Answer 1

5-15mmHg

Question 2

Intracranial pressure range in children

Answer 2

5-7mmHg

Question 3

Intracranial pressure range in term infants

Answer 3

1.5-6mmHg

Question 4

What is intracranial pressure determined by?

Answer 4

Volume of blood
CSF
Brain

Question 5

What is Monro-Kellie doctrine hypothesis?

Answer 5

Any increase in the volume of one of the intracranial constitutes must be compensated by a decrease in the volume of one of the others

Question 6

What are the first components to be pushed out of the intracranial space when there is an intracranial mass?

Answer 6

CSF
Venous blood

Question 7

Cerebral perfusion pressure calculation

Answer 7

CPP = mean arterial pressure - ICP

Question 8

What can cause raised ICP?

Answer 8

Too much CSF, blood or brain

Question 9

What is hydrocephalus?

Answer 9

Build up of CSF within the brain

Question 10

Management of hydrocephalus

Answer 10

• acutely by tapping fontanelle with needle
• medium term drainage by external ventricular drain
• long term by ventricular shunts: tube between ventricular system + peritoneum or right atrium

Question 11

Clinical signs of hydrocephalus

Answer 11

• bulging head with head circumference increasing faster than expected
• sunsetting eyes

Question 12

Acquired causes of hydrocephalus

Answer 12

• meningitis
• trauma
• haemorrhage e.g. post subarachnoid haemorrhage
• tumours e.g. compressing cerebral aqueduct

Question 13

What is cerebral blood flow dependent on?
When can it not be maintained?

Answer 13

Cerebral perfusion pressure
If CPP <50mmHg

Question 14

Outline cerebral auto regulation in regards to mean arterial pressure + ICP

Answer 14

• if MAP increases > CPP increases > triggers cerebral autoregulation > vasoconstriction of cerebral arterioles
• if ICP increases > CPP decreases > triggers cerebral auto regulation > vasodilation of cerebral arterioles

Question 15

Outline Cushing’s triad/response/reflex

Answer 15

• rise in ICP > hypertension as body increases MAP to maintain CPP
• increase in MAP > detected by baroreceptors > bradycardia via increased vagal stimulation
• continuing compression of brain steam leads to damage to respiratory centres > irregular breathing

Question 16

Four major pathophysiologies of cerebral oedema

Answer 16

• vasogenic
• cytotoxic
• osmotic
• interstitial
  ***

Question 17

Clinical features of raised ICP

Answer 17

• constant headache which worsens on bending/straining + in morning
• N + V
• double vision
• visual field defects
• papilloedema
• seizures
• reducing GCS - confusion, drowsiness, unconscious
• focal neurological signs

Question 18

Epidemiology idiopathic intracranial hypertension

Answer 18

obese middle aged females

Question 19

Diagnosis of idiopathic intracranial hypertension

Answer 19

Confirmed by raised opening pressure on lumbar puncture

Question 20

Treatment of idiopathic intracranial hypertension

Answer 20

Weight loss
Blood pressure control

Question 21

Types of brain herniation

Answer 21

• tonsillar herniation (coning)
• uncl herniation
• subfalcine hernation
• central downward herniation
• external herniation

Question 22

Outline tonsillar herniation (coning)

Answer 22

Cerebellar tonsils herniate through foramen magnum > compression of medulla

Question 23

Outline subfalcine herniation

Answer 23

Cingulate gyrus herniates under free edge of Falx cerebri > compression of anterior cerebral artery as it loops over corpus callosum

Question 24

What is vulnerable in a subfalcine herniation?

Answer 24

Anteior cerebral artery as it loops over corpus callosum

Question 25

Outline uncl herniation

Answer 25

- **Uncus of temporal lobe herniates through tentorial notch** > compresses adjacent midbrain - can cause oculomotor nerve palsy + blown pupil - can cause contralateral hemiparesis due to compression of cerebral peduncle

Question 26

Outline central downward herniation

Answer 26

Medial temporal lobe + other midline structures pushed down through tentorial notch

Question 27

Outline external herniation

Answer 27

Brain herniation through skull fracture or therapeutic craniectomy

Question 28

What is Cushing’s triad?

Answer 28

Hypertension Bradycardia Irregular breathing

Question 29

Management of a patient with acutely raised ICP

Answer 29

- **maintain O2 + remove CO2** - **maintain MAP** > maintains CPP - **sedation, analgesia + paralysis**: decreases metabolic demand + prevents coughing + shivering that might increase ICP more - **elevate head of bed 10-15°**: maximises cerebral venous return - **prevent hyperthermia** - **anticonvulsants**

Question 30

Ongoing management of raised ICP

Answer 30

- **osmotic diuresis**: *e.g. mannitol or hypertonic saline* - **regular re-evaluation + monitoring** - **surgical intervention**: evacuation of haemorrhage, ventricular drainage, evacuation of haemorrhage

Question 31

Examples of surgical intervention of raised ICP

Answer 31

- evacuation of haemorrhage - ventricular drainage - decompressive craniectomy

Question 32

Generally what is classed as high ICP?

Answer 32

>20mmHg

Question 33

If a patient has hypertension + raised ICP, why should you not attempt to lower it?

Answer 33

May be directly driving perfusion to ischaemic areas of brain

Question 34

Why can hydrocephalus cause sunsetting eyes?

Answer 34

Direct compression of orbits + oculomotor nerve as i exits midbrain