Raised ICP

Question 1

What are the normal intracranial pressures (CSF pressure) for Adults, children and term infants?

Answer 1

• Adults: <10-15 mmHg
• Children: 3-7 mmHg
• Term infants: 1.5-6 mmHg

Question 2

How can you measure ICP?

Answer 2

• Lumbar puncture
• Subdural ICP monitor
• Subarachnoid ICP monitor
• Epidural ICP monitor
• many more…

Question 3

What is NIRS?

Answer 3

Near Infra-Red Spectroscopy

• Meaures ICP indirectly by measuring cerebral perfusion
• Relies on the transparency of tissue for light int he NIR range and O₂ dependent light absorbance of Hb

Question 4

What is the normal ICP wave? What kind of things will increase ICP normally?

Answer 4

Usually P1> P2

Normally increased by; cough, respiration, valsalvar manouvre

Question 5

How can the ICP wave change in acute brain injury?

Answer 5

A change in brain injury compliance causes the reversal of P1:P2 and P2> P1

Question 6

What are some of the immediate compensatory mechanisms that kick in when ICP is raised?

Answer 6

• Decrease in CSF volume → fluid moves into lumbar area
• Reduced CSF production
• Decreased blood volume → blood squuezed out of the sinuses

Question 7

What delayed mechanism acts to reduce raised intracranial pressure?

Answer 7

Decrease in extracellular fluid

Question 8

What is the Monro-Kellie doctrine?

Answer 8

The sum of intracranial volumes within brain and CSF and other components (tumour, haemaotoma) is constant

Intracranial volume rises gradually then rapidly to the point where the brain can b squeezed out of the foramen magnum

Question 9

How does ICP relate to cerebral perfusion?

Answer 9

Cerebral perfusion pressure = MAP - ICP

Question 10

What are the 2 major consequences of increased ICP?

Answer 10

• Brain shifts
• Brain ischemia

Question 11

What are some of the symptoms and signs of rICP?

Answer 11

Symptoms

• Headache
• Nausea and vomting
• Double vision
• Neurological symptoms

Signs

• Bradycardia
• Systolic hypertension
• Irregular respiration
• Cheyne Stokes respirations
• Decreased mental abilities
• Confusion
• Non-reactive pupils
• Loss of conciousness
• Pappiloedema

Question 12

What is Cushing’s reflex?

Answer 12

Question 13

What is craniosynotosis?

Answer 13

Early fusion of the sutres of the skull → not enough rough for the expanding brain

Question 14

What should you not do to patients who have raised ICP?

Answer 14

Do not push in lots of fluids!

Question 15

Explain what happens due to ICP in extradural haemorrhage?

Answer 15

• Patient presents with loss of conciousness on initial injury
• followed by transient recovery‘lucid interval’ (in 40% patients)
• As haematoma enlarged, ICP rises compressing the brain → deteriorating conciousness
• May see cranial nerve palsies as brain structures start to herniate

Question 16

How do extradural haemorrhages occur?

Answer 16

• collection of blood between the inner surface of the skull and the periosteal dura mater
• Nearly always secondary to trauma
• 90% of cases involved in a severed artery - commonly middle meningeal artery

Question 17

What happens in subdural haemorrhage?

Answer 17

• Usually occurs in older patients where the brain shrinks and bridging beins under more tension
• More fragile → vulnerable to break

Question 18

How can you reduce ICP?

Answer 18

• Start by standard measures; airways control, ABC, ventilation
• Tier 2; sedation, fever control, glucocorticoids and try hyperosmolar & diversion therapy, diuretics
• Tier 3; barbituate coma (avoids epilepsy and rests the brain)
• Eventually may need decompressive craniectomy or burr hole surgery

Question 19

Why can you get a fixed and dilated pupil in rICP?

Answer 19

• Increased ICP can compress the occulomotor nerve
• Responsible for pupil dilation and eye movements

Question 20

What can cause communicating hydrocephalus?

Answer 20

• Abnormalities of the arachnoid granules that absorb CSF mean CSF isn’t absorbed → ICP rises
• Impaired CSF reabsorbtion in the absence of any obstruction

Question 21

What can cause non-communicated hydrocephalus?

Answer 21

• Due to CSF flow obstuction
• Blockage of:
  
  • ​Foramen of Monro
  • Aqueduct of sylvius
  • 4th ventricle obstruction
  • Foramen of luschka and magendie

Question 22

What is Budd Chiari malformation?

Answer 22

• Structural anatomical defect where the cerebellum tonsils are displaced downwards through the foramen magnum
• More extremely can involve cerebellum, brainstem and 4th ventricle

Question 23

Why do you get oedema in an anoxic brain injury?

Answer 23

• Decreased cerebral blood flow
• Decreased O₂
• Na/K ATPase cannot function
• Efflux K⁺ out of cell
• Influx Na⁺ into the cell
• Neurones become depolarised
• Water will follow Na into the cell → oedema