Clinical Aspects of Cerebral Perfusion and ICP

Question 1

What does the intracranial cavity contain

Answer 1

Nervous tissue
Blood vessels
Venous channels
CSF

Question 2

What is the normal intracranial pressure

Answer 2

5-15 mmHg

Question 3

What raise in icp will be pathological

Answer 3

Sustained increase above 20mmHg
can increase and decrease during transient activities (sneezing, straining, getting up from lying down)

Question 4

What is the Monro-Kellie hypothesis

Answer 4

Intracranial volume is fixed due to non-compliant skull
Contents non-compressible
Change in volume of contents or addition of new space occupying lesions = increased pressure
unless reduction of other content

Question 5

What are the percentages of the contents in the intracranial cavity

Answer 5

CSF volume: 150ml, 10%
Blood volume: 150ml, 10%
Brain parenchyma volume: 1400ml, 80%

Question 6

What is the trend of increasing ICP

Answer 6

Brain has minimal compliance
ICP starts increasing very minimally
Once increasing volume cannot be compensated further
ICP increases exponentially

Question 7

What can the Intracranial cavity do to try compensate raising ICP

Answer 7

Reduction of venous blood
Displacement of CSF towards spine
Reduction CSF volume

Once these cannot compensate further for the raising ICP it will increase exponentially

Question 8

What are types of pathologies that can cause a raised ICP

Answer 8

localized shifts of brain across various compartments
focal or global reduction of blood flow
Focal or global ischemia
Reduced energy production
Pump failure on cell membrane
Cellular dysfunction
Interstitial microenvironment changes (toxic metabolites)
membrane damage and cell death

Question 9

What are the 3 peaks in ICP waveform

Answer 9

P1: percussion wave, arterail pulsation
P2: Tidal wave, intracranial compliance
P3: Dicrotic wave, venous pulsation

Question 10

What does a normal ICP waveform look like

Answer 10

P1 highest upstroke, then P2, then P3

Question 11

What would suggest intracranial hypertension suggest on ICP waveforms

Answer 11

P2 is higher than P1

Question 12

What does P2>P1 indicate

Answer 12

Intracranial hypertension

Question 13

What are the two different types of waveform pulses

Answer 13

Vascular pulse: one waveform, top to bottom of wave
Respiratory pulse: many waverforms, top valve to bottom value

Question 14

What can measure intracranial pressure

Answer 14

Subarachnoid (richmond) bolt, prefered method

EVD, tunneled EVD (external ventricular drainage)
epidural bolt

Question 15

what is normal cerebral blood flow

Answer 15

700ml/min, 50ml/100g/min cerebral blood flow
roughly 14% of cardiac outflow

Question 16

what is the normal cerebral blood flow to white and grey matter

Answer 16

Grey matter: 70ml/100g/min
White matter: 20ml/100g/min

Question 17

What does CBF depend on

Answer 17

MAP
Intracranial pressure
Vascular resistance
Autoregulatory mechanisms of brain

Question 18

What is the cerebral perfusion pressure

Answer 18

MAP - ICP

Question 19

what is the cerebro-vascular resistance (CVR)

Answer 19

resistance from cerebral vascular to flowing blood

Question 20

What do the autoregulation mechanisms do

Answer 20

maintain constant blood flow over wide range of pressures
Brain can also increase blood flow to specific regions when they are active

Question 21

What is mean arterial pressure (MAP)

Answer 21

Systolic - diastolic pressure

Question 22

What are the four autoregulation mechanisms

Answer 22

Autonomic neurogenic theory
endothelial mechanims
myogenic autoregulation
Metabolic autoregulation (PaCO2 significant influencer on CBF, PaO2 influences if it drops significantly)

Question 23

Why is CBF, ICP and autoregulation so important

Answer 23

Brain uses glucose and ketones for metabolism
Has no stored energy source
Impaired blood flow: mitochondrial energy production failure –> cell death within minutes
Injured brain loses ability to autoregulate: hyper/hypotension, hypoxia and raised ICP lead to secondary insult.

Question 24

What does neuromonitoring involve

Answer 24

ICP measurements and maintenance of CPP
Measures CPP by meausuring MAP and ICP
preventing insult: reduce ICP and prevent high or low CPP