cerebral blood flow

Question 1

3 main components of the intracranial vault

Answer 1

CSF 10-15%
Brain 80-85%
Blood 5-10% (60-80 ml)

Question 2

CSF occupies what space and is created where

Answer 2

• occupies subarachnoid space (bathes brain and spinal cord)
• produced in the choroid plexus

Question 3

properties of CSF

Answer 3

• 10% of intracranial volume
• 500 cc produced/ day
• volume 150ml at any given time

Question 4

circle of willis flow

Answer 4

• bifurcates into the external and internal carotid arteries
• internal branch enters the base of the skull
• arterial supply of the eye via ophthalmic artery
• ultimately bifurcates into anterior and middle cerebral arteries

Question 5

what provides anterior circulation to the brain

Answer 5

• carotid arteries

Question 6

what provides posterior circulation to the brain

Answer 6

• vertebral arteries

Question 7

venous system of the brain

Answer 7

• venous blood drains into the venous sinus which are between layers of dura mater and drain into IJ
• valveless
• negative pressure (air embolism)
• little influence on ANS

Question 8

global blood flow

Answer 8

45-55 ml/ 100g/ min

Question 9

cortical blood flow (grey matter)

Answer 9

75-80 ml/ 100g/ min

Question 10

subcortical blood flow (white matter)

Answer 10

20 ml/ 100g/ min

Question 11

CMRO2

Answer 11

3 - 3.5 ml/ 100g/ min

Question 12

Cerebral venous Po2

Answer 12

32-44 mmHg

Question 13

cerebral venous So2

Answer 13

55-70%

Question 14

normal ICP

Answer 14

10-15 mmHg

Question 15

dangerous cerebral flows

Answer 15

< 30 ml/ 100g/ min = ischemia
< 20 ml/ 100g/ min = abnormal EEG
< 15 ml/ 100g/ min = irreversible damage
- brain has no significant reserves (8-FiO2 encouraged)

Question 16

relationship between CMRO2 and CBF

Answer 16

• increased CMRO2 = increased CBF

Question 17

what controls CBF

Answer 17

• CPP determines CBF
• ICP = CVP
• normal CVP 70-100 mmHg

Question 18

autoregulation of CBF

Answer 18

• MAP between 60-150 mmHg, CBF remains constant
• chronic HTN changes the range

Question 19

loss of autoregulation occurs with

Answer 19

• acidosis
• hypoxia
• trauma
• volatile anesthetics

Question 20

Monro-Kelly Doctrine

Answer 20

• ICP is stable as long as volume added is balanced by volume displaced

Question 21

metabolic autoregulation compensation

Answer 21

• balance of acid/base & oxygenation
• vasoconstriction or dilation of cerebral vessels to increase or decrease blood supply to the brain to rid waste products

Question 22

metabolic autoregulation decompensation

Answer 22

• hypoxia or acidosis trigger vasodilation
• blood supply increases but compromised brain cant handle increased ICP and lactic acid

Question 23

CBF change for 1mmHg PaCO2

Answer 23

CBF changes by 4% (1-2ml) for each 1mmHg change in PaCO2
- CBF is most sensitive to CO2 (fast response)

Question 24

H+ and CBF

Answer 24

• increased H+ = increased CBF
• slower onset

Question 25

what PaO2 level causes vasodilation

Answer 25

< 50 mmHg
venous O2 below 30 = increased CBF

Question 26

how much O2 does the brain use

Answer 26

• 15-20% of body’s O2 consumption

Question 27

how is glucose obtained

Answer 27

• 85-90% of glucose is obtained by an oxidative pathway
• without O2 no glucose is utilized