10.1.1 Raised Intrcranial Pressure

Question 1

Define intracranial pressure

Answer 1

• Pressure of the CSF within the subarachnoid space
• Normal pressure varies with age
• Normal ICP in an adult less than 10-15mmHg
• Normal ICP has a pulsatile wave pattern with 2 components; an arterial and respiratory wave

Question 2

What does the arterial wave consist of?

Answer 2

P1 - arterial pulse
P2 - intracranial compliance
P3 - aortic valve closure, dicrotic notch

P = pulse

Question 3

How does the respiratory wave work?

Answer 3

• Inspiration. - negative intrathoracic pressure; ⬇️ ICP
• Expiration - positive intrathoratic pressure; ⬆️ ICP

Question 4

Monro-Kellie

Answer 4

• The skull is non expansible and has a fixed volume
• Brain (1200ml-1400ml)
• Blood (120-150ml)
• CSF (75ml)
• Monro-Kellie doctrine - sum of volumes of brain, CSF and intracranial blood is constant

Question 5

Cerebral Perfusion Pressure

Answer 5

CPP=MAP-ICP mmHg

• CPP= cerebral perfusion pressure (net pressure gradient that drives O2 delivery to cerebral tissue)
• MAP= mean arterial pressure
• ICP = intra-cranial pressure

Question 6

Cerebral blood flow

Answer 6

Flow = pressure ÷ resistance

CBF=CPP÷CVR
- CBF = cerebral blood flow (normal 54ml/100g tissue/min)
- CPP = cerebral perfusion pressure
- CVR = cerebral vascular resistance

Question 7

Cerebral blood flow auto regulation

Answer 7

Cerebral smooth muscle:
- constricts in response to elevated pressure (⬆️CVR)
- dilates in response to decreased pressure (⬇️CVR)

Question 8

Define Raised intracranial pressure

Answer 8

• Sustained pressure of 20 mmHg is seen as pathological
• Physiological increases in ICP take place during: coughing, Valsalva, head- down position, compression of the neck veins
• Raised pressure can take different forms: slowly increasing pressure (chronic raised ICP); rapidly increasing pressure (acute raised ICP)

Question 9

Causes of raised intracranial pressure

Answer 9

Traumatic
- Intracranail bleeds (extradural, subdural, intracerebral hematoma
- Cerebral oedema

Neoplastic
- Primary brain tumors (astrocytoma, glioblastoma, meningiomas)
- Secondary brain tumors (metastases from lung, breast, melanoma, renal and colorectal tumors

Infective
- Abscess (bacterial, TB, fungal)
- Cysts (parasite)
- Granuloma (TB, Syphilis)

CSF
- Hydrocephalus (decreased absorption or increased production) -> accumulation

Vascular
- Hemorrhagic stroke
- Ischemic stroke (brain swell)

Question 10

Symptoms of raised intracranial pressure
Acute
Chronic

Answer 10

Acute raised ICP
- Decreased level of consciousness
- Herniation syndromes

Chronic raised ICP
- Headache (worse in morning; worse when bending forward, Valsalva; better after vomiting (hyperventilation))
- Vomiting (worse in morning)
- Papilledema - Raised CSF pressure in the optic nerve sheath causes decreased axoplasmic transport in the optic neurones and swelling of the optic cup

Question 11

Complications of raised intracranial pressure

Answer 11

• The harmful effects of raised intracranial pressure are primarily due to brain injury caused by cerebral ischemia
• Cerebral ischemia is the result of decreased brain perfusion secondary to increased ICP
• Raised ICP can lead to cerebral herniation
• If left untreated will ultimately lead to death

Question 12

Which electrolyte is important in fluid homeostasis in a head injury

Answer 12

Sodium

Question 13

Secondary head injury that can directly lead to raised intracranial pressure

Answer 13

Hypercapnoea

Question 14

Normal cerebral metabolic rate of O2 in brain

Answer 14

3.5 ml/100g/min