Alterations in Cerebral Homeostasis Flashcards
Cerebral Blood Flow
CBF
normally regulated to meet metabolic needs of the brain
20% of cardiac output goes to the brain
750-900ml of blood per minute
altered by CO2 and oxygen
CBF decreases when CO2 decreases
CBF increases when PaO2 is < 50mmHg
PaO2 of 80 maintains CBF
Cerebral perfusion pressure
perfusion pressure that is needed to perfuse the brain
CPP= MAP - ICP
normal is 70-90 mmHg
Increased intracranial pressure
results from tumor, edema, excess CSF, or hemorrhage
first compensation method is dumping CSF
normal ICP 5-15
stage 1 of ICP
compensates for ICP by vasoconstriction and external compression of the venous system
stage 2 of ICP
increases amount of contents inside cranial vault
surpassed ability to compensate
-S/S appear
confusion, restlessness, lethargy, pupil and breathing changes, decreased LOC (first sign of increases ICP)
Stage 3 of ICP
cellular hypoxia and hypercapnia begins
decompensation quickly
decreased LOC, widening pulse pressure bradycardia, pupils small and sluggish, arterial autoregulation is lost, arterial vasodilation and CO2 accumulation occur
decreases hydrostatic pressure and increases blood volume
Stage 4 of ICP
Herniation and the equalization of arterial pressure and ICP
equal pressure –> prevent CPP/CBF
Herniation high pressure to low pressure
Supratentorial Herniation
above the tectorial membrane
- Uncal Herniation
compresses 3rd cranial nerve and mesencephalon
decreases LOC, posturing, one pupil dilated than the other, cheyenne stroke RR
-Central Herniation
diencephalon forced down
LOC quickly, apnea, small reactive pupils and later dilate, posturing.
-Cingulate Gyrus Herniation
moves brain laterally
-Transcalvarial Herniation
brain tissue moving through opening in the skull
skull fx or sx opening
Infratentorial herniation
cerebellar tonsillar herniation
- most common
downward movement of the cerebellum through the foramen magnum
stiff neck, decrease LOC respiratory abnormalities and pulse variations
