CMRO2

Question 1

CBF Formula

Answer 1

CPP / CVR

Question 2

What is the CRMO2 blood flow per minute

Answer 2

3.0 - 3.8 ml/O2/100g brain tissue/min

Question 3

How much is CMRO2 increased/decreased per 1˚C change?

Answer 3

7%

Question 4

Global CBF (ml/min)

Answer 4

45 - 55 ml/100g brain tissue/min

Question 5

Cortical CBF (ml/min)

Answer 5

75 - 80 ml/100g brain tissue/min

Question 6

Subcortical CBF (ml/min)

Answer 6

20 ml/100g brain tissue/min

Question 7

Critical values for global CBF

Answer 7

~ 20 ml/min = evidence of ischemia
~ 15 ml/min = complete cortical suppression
< 15 ml/min = cellular brain death

Question 8

What are the 5 determinants of CBF?

Answer 8

PaCO2
PaO2
Venous pressure
CPP
CMRO2

Question 9

What % of O2 (of global CBF) is used for electrical vs cellular activity?

Answer 9

Electrical = 60%
Cellular = 40%

Question 10

Does the brain consume O2 with brain silencing?

Answer 10

Yes

Question 11

At what ˚C does EEG suppression occur?

Answer 11

18 - 20˚C

Question 12

What factors decrease CMRO2?

Answer 12

Hypothermia
Propofol
Etomidate
Barbiturates
Halogenated anesthetics

Question 13

What factors increase CMRO2?

Answer 13

Hyperthermia
Seizures
Ketamine
N2O

Question 14

What does it mean when we say that volatile anesthetics “uncouple” CMRO2 from CBF?

Answer 14

Even though the need for CMRO2 is decreased, volatile anesthetics still cause cerebral vascular dilation and increase CBF

Question 15

At what ˚C is the brain protected the most?

How long does this protective mechanism last?

Answer 15

32 - 34˚C

12 - 24 hours

Question 16

What ˚C will denaturation of proteins and neurons occur?

Answer 16

> 42˚C

Question 17

Between what CPP values is auto-regulation greatest?

Answer 17

50 - 150 mmHg

Question 18

Between what MAP values is auto-regulation greatest?

Answer 18

60 - 160 mmHg

Question 19

At what PaCO2 value does max vasoconstriction of cerebral vessels occur?

Answer 19

25 mmHg

Question 20

At what PaCO2 value does max vasodilation of cerebral vessels occur?

Answer 20

80 - 100 mmHg

Question 21

What things abolish the auto-regulation curve?

Answer 21

Volatile anesthetics
Head trauma
Intracranial tumor

Question 22

How much does CBF increase/decrease in relation to PaCO2 values?

Answer 22

1 - 2 ml/100g brain tissue/min for every 1 mmHg change in PaCO2

Question 23

Describe “cerebral steal”

Answer 23

Situation in which the administration of cerebral vasodilators, use of volatile anesthetics, hyperventilation, etc. will cause cerebral vascular dilation to healthy brain tissue and “steal” from already maximally dilated ischemia areas of the brain

Question 24

Describe “inverse steal”

Answer 24

AKA “Robinhood Effect” - describes the method of utilizing hyperventilation to vasoconstrict cerebral vessels supplying healthy brain tissue in an attempt to provide increased blood flow to ischemic vessels that are already maximally vasodilated

Question 25

What is the best PaCO2 to maintain adequate cerebral blood flow?

Answer 25

PaCO2 between 30 - 35 mmHg

Question 26

1. What happens with a PaO2 of 50 - 60 mmHg? | 2. What about > 60?

Answer 26

1. Cerebral vasculature vasodilation to support increased needs for O2 delivery 2. No change > 60 mmHg

Question 27

How does venous pressure affect ICP?

Answer 27

Increased venous pressure reduces venous drainage from the brain and increases cerebral volume - both of which increases ICP

Question 28

What factors reduce cerebral drainage and increase venous pressure?

Answer 28

Vena cava syndrome Jugular vein compression (improper positioning) Increased intrathoracic pressure (i.e. PEEP) Vena cava thrombosis