Cerebral perfusion and ICP

Question 1

How much of the cardiac output does the brain receive?

Answer 1

15%

Question 2

Normal cerebral blood flow

Answer 2

55-60ml/100g brain tissue

Question 3

Grey matter blood flow

Answer 3

75ml/100g/minute

Question 4

White matter blood flow

Answer 4

45ml/100g/minute

Question 5

Ischaemia occurs at which cerebral blood flow?

Answer 5

20ml/100g/minute

Question 6

Permanent damage occurs at what cerebral blood flow?

Answer 6

below 10ml/100g/minute

Question 7

What is the most significant factor determining cerebral blood flow?

Answer 7

CPP

Question 8

What is Cerebral perfusion pressure?

Answer 8

The effective blood pressure gradient across the brain

Question 9

CPP=?

Answer 9

MAP-ICP

Question 10

How do you calculate MAP?

Answer 10

DP +1/3 PP or 2/3DP+1/3SP

Question 11

When ICP increases what happens to CPP?

Answer 11

decreases

Question 12

3 factors regulating cerebral blood flow

Answer 12

CPP
concentration of arterial PCO2
arterial PO2

Question 13

What is cerebral autoregulation?

Answer 13

The ability to maintain constant blood flow to the brain over a wide range of CPP (50-150mmHg)

Question 14

If CPP is low what do cerebral arterioles do?

Answer 14

dilate to compensate at decreased pressure

Question 15

If CPP is high what happens to cerebral arterioles?

Answer 15

constrict

Question 16

Over what CPP pressure does autoregulation fail?

Answer 16

150mmHg

Question 17

Give 3 examples of scenarios in which autoregulation would fail

Answer 17

hypertensive crisis
toxins eg CO2
first 4-5 days after head trauma

Question 18

What is cerebral oedema?

Answer 18

State of increased brain volume as a result of an increase in water content

Question 19

What is cerebral oedema a prominent cause of?

Answer 19

subacute to chronic intracranial hypertension

Question 20

What is the blood brain barrier?

Answer 20

A barrier composed of astrocytic foot processes wrapping around a capillary endothelium composed of tight junctions

Question 21

When does vasogenic oedema occur?

Answer 21

disruption in blood-brain barrier

Question 22

How are lipid soluble substances passed across capillary endothelial cells?

Answer 22

passively

Question 23

How are amino acids and sugars passed across capillary endothelium?

Answer 23

specific carrier mediated mechanisms

Question 24

What is the monro-kelly doctrine principle simply?

Answer 24

cranium is a rigid structure
fixed volume of brain, CSF and blood
new mass introduced leads to change in volume in other

Question 25

What volumes can decrease with the monro-kely doctrine principle?

Answer 25

CSF and blood

Question 26

How are CSF and venous blood shunted out of the brain to compensate for increasing cranial volume?

Answer 26

IJV/emissary and scalp veins spinal cord - foramina of luschka and magendie into spinal subarachnoid space

Question 27

What is compliance?

Answer 27

change in volume observed for a given change in pressure

dV/dP

Question 28

What is elastance?

Answer 28

inverse of compliance
change in pressure observed for a given change in volume
dP/dV

Question 29

What does elastance represent?

Answer 29

The accommodation to outward expansion of an intracranial mass

Question 30

What happens when homeostatic mechanisms are depleted and critical volume is reached?

Answer 30

small volume changes result in large increase in pressure and hypertension occurs

Question 31

What is cushings reflex?

Answer 31

vasopressor response

hypertension, irregular breathing and bradycardia

Question 32

Management methods of increased ICP

Answer 32

elevate head 
mannitol/hypertonic saline
hyperventilation 
barbiturate coma 
surgical decompression