Intracranial Pressure and Cerebral Blood Flow

Question 1

What does the intracranial cavity contain?

Answer 1

Nervous tissue, blood vessels, venous channel and CSF

Question 2

What is normal ICP cm of water?

Answer 2

5-15cm, can rise or decrease with sneezing, straining and getting up
Beyond 20 cm is pathological

Question 3

Describe the Monro-Kellie hypothesis

Answer 3

Intracranial volume is fixed due to non-compliant skull
Contents are non compressible
Change in volume or addition of new space increases pressure unless compensated by reduction

Question 4

What can a large extradural hematoma cause?

Answer 4

Compensation
Reduction in venous blood, displacement of CSF towards spine and reduction in CSF volume
Brain has minimal compliance - if cant compensate then increase ICP

Question 5

Describe the pathology of raised ICP

Answer 5

Localised shift of brain across compartments, reduction of blood flow, ischaemia, reduced energy production, pump failure on membrane, cellular dysfunction and interstitial microenvironment changes - toxic metabolites

Question 6

How is ICP measured?

Answer 6

EVD into lateral ventricle
Shows waves of ICP

Question 7

What does ICP depend on?

Answer 7

Vascular pulse and resp. pulse

Question 8

What is normal cerebral blood flow?

Answer 8

700ml/min
14% of cardiac output
Regional variation in flow depending on demand

Question 9

What is the mean arterial pressure?

Answer 9

MAP - diastolic pressure plus one third of pulse pressure (difference between systolic and diastolic)

Question 10

What is cerebral perfusion pressure?

Answer 10

CPP - difference between mean arterial pressure MAP and intracranial pressure ICP

Question 11

What is cerebro-vascular resistance?

Answer 11

CVR - resistance offered by cerebral vasculature to flowing blood

Question 12

What is autoregulation?

Answer 12

Ability of brain to maintain constant blood flow over side range of pressure

Question 13

What does cerebral blood flow depend on?

Answer 13

MAP (driving blood into cavity)
ICP (creates gradient)
Vascular resistance (low resistance then higher flow)
Autoregulatory mechanisms

Question 14

What is an example of autoregulation?

Answer 14

Brain can increase blood flow to specific regions in brain if they are active like temporal lobe during speech

Question 15

What are some autoregulation mechanisms?

Answer 15

Autonomic neurogenic theory
Endothelial mechanisms
Myogenic autoregulation
Metabolic autoregulation - PaCO2 and PaO2 only it is significant drop

Question 16

What is the importance of CBF, ICP and autoregulation?

Answer 16

Brain tissue uses glucose and ketones exclusively for metabolism
Brain tissues have no stored energy stores
Impaired blood flow - mitochondrial energy production failure so cell death
If injury then loss of autoregulation - hypo/hypertension, hypoxia and raised ICP

Question 17

What does disruptions in dynamic balance between CBF, cerebral venous outflow, CSF production/ absorption and brain volume?

Answer 17

Brain damage and disease

Question 18

What can happen in head injury?

Answer 18

Raised ICP
Hypotension and hypoxia
Autoregulation lost

Question 19

Describe neuromonitoring

Answer 19

Continuous monitoring of ICP with surgical implanted pressure transducer
Measurement of CPP by measuring MAP and ICP
Reducing ICP and preventing high or low CPP

Question 20

What are other ICP and cerebral blood flow conditions?

Answer 20

Hydrocephalus, stroke, venous outflow obstruction, tumours and brain haemorrhage