CMRO2 Flashcards
CBF Formula
CPP / CVR
What is the CRMO2 blood flow per minute
3.0 - 3.8 ml/O2/100g brain tissue/min
How much is CMRO2 increased/decreased per 1˚C change?
7%
Global CBF (ml/min)
45 - 55 ml/100g brain tissue/min
Cortical CBF (ml/min)
75 - 80 ml/100g brain tissue/min
Subcortical CBF (ml/min)
20 ml/100g brain tissue/min
Critical values for global CBF
~ 20 ml/min = evidence of ischemia
~ 15 ml/min = complete cortical suppression
< 15 ml/min = cellular brain death
What are the 5 determinants of CBF?
PaCO2 PaO2 Venous pressure CPP CMRO2
What % of O2 (of global CBF) is used for electrical vs cellular activity?
Electrical = 60% Cellular = 40%
Does the brain consume O2 with brain silencing?
Yes
At what ˚C does EEG suppression occur?
18 - 20˚C
What factors decrease CMRO2?
Hypothermia Propofol Etomidate Barbiturates Halogenated anesthetics
What factors increase CMRO2?
Hyperthermia
Seizures
Ketamine
N2O
What does it mean when we say that volatile anesthetics “uncouple” CMRO2 from CBF?
Even though the need for CMRO2 is decreased, volatile anesthetics still cause cerebral vascular dilation and increase CBF
At what ˚C is the brain protected the most?
How long does this protective mechanism last?
32 - 34˚C
12 - 24 hours