ICP and brain herniation Flashcards
what components of the brain contribute to intracranial pressure
- CSF (10%)
- brain tissue (78%)
- intravascular blood (12%)
what is the phenomenon when all three factors that contribute to ICP are in equilibrium
Monroe Kellie doctrine
what is the normal range for ICP
5 to 15 mmHg
when do we consider ICP to be elevated
when it is above 20mmHg
what 6 factors influence ICP
arterial pressure
venous pressure
intra-abdominal and intra-thoracic pressure
posture
temperature
blood gases
what are the compensatory adaptations for change in ICP
change in CSF volume
change in intracranial blood volume
change in tissue brain volume
what affects compensation of ICP
if the volume increases continues and ICP increases further then there will be decompensation
what is cerebral blood flow and how is it divided
the amount of blood in milliliters that passes through 100g of brain tissue per minute
about 50ml/min per 100g of white matter
about 170ml/min per 100g of grey matter
what factors of BP need to be satisfied for the brain to get its nutrients
Mean Arterial pressure needs to be higher than ICP
what is cerebral perfusion pressure (CPP)
the pressure needed to overcome the ICP in order to deliver O2 and nutrients to the brain
how do you calculate CPP
CPP = MAP - ICP
what happens when CPP is less than 50mmHg
brain ischaemia
what happens when CPP is less than 30mmHg
brain death
what is the normal CPP
88mmHg
what factors regulate CBF
autoregulation
metabolic regulation
what happens with autoregulation
blood vessel diameter changes in order to ensure consistent CBF
and this is only effective if MAP is between 70 and 150. when its outside those ranges the Pa02 levels gets affected
what metabolic factors get regulated
PCO2
PO2
Acidosis
what are the causes of increased ICP
mass lesions
cerebral oedema
head injury
brain inflammation
metabolic insult
what happens in the event of sustained increase in ICP
brain compression and brain herniation
what are the 6 types of brain herniation
upward herniation
central herniation
tonsilar herniation
subfalcine herniation
transtentorial herniation
transcalvarial herniation
what happens in subfalcine herniation
Ipsilateral cingulate gyrus gets pushed beneath falx cerebri and this causes infarction of distal territory of ACA
what happens in transtentorial herniation
ipsilateral medial temporal lobe is squeezed under and across tentorium cerebelli
this causes compression of CN3, compression of cerebral aqueduct which will cause hydrocephalus
the infarction is on the temporal or occipital lobe
where do you find a kernohans notch
transtentorial herniation
what happens in central herniation
the thalamu and hypothalamus and the medial parts of the temporal lobe are forced though the tentorial notch
this will destruction of chiasmatic cistern and this will cause pin point pupils and duret haemorrhages
what happens in tonsilar herniation
= infratentorial mass forces cerebellar tonsils through foramen magnum
compression of the brainstem leading to coma and death
compression of PICA and vertebral arteries causing ischaemia of brainstem. tonsils and lower cerebellum
what happens with upward herniation
infratentorial mass compresses the brain stem causing displacement of the brainstem and the cerebellum
this ultimately results to occlusion of PCA and SCA leading territorial infarct
cerebrum pushes cerebral aqueduct causing hydrocephalus
what happens in transcalvarial herniation
displacement of the brain through the defects in the skull
