ICP Flashcards
What are the three main components of the Intracranial vault?
- brain: 80-85%
- blood: 5-10%
- CSF: 10-15%
The _______ _________ is a rigid, non-expandable structure that protects the brain.
Adult cranium
At what ICP is there limit of compensation?
Up to ~ 20 mmHg
At what ICP is focal ischemia seen?
20-50mmHg
At what ICP is there global ischemia?
> 50mmHg
What is the normal ICP?
5-15 mmHg
When should treatment for intracranial HTN be initiated?
There is no defined set point at which treatment for intracranial HTN should be initiated, but levels above 20 mmHg are usually treated.
However, it is probably more important to maintain an adequate cerebral perfusion pressure.
Where is CSF produced?
By the choroid plexus in the cerebral ventricles
Where is CSF found?
Surrounding the brain and spinal cord
How much CSF is produced?
500 cc produced every 24 hours
Total volume of CSF is roughly 150 cc
How is CSF drained for chronic hydrocephalus?
With VP shunts
How is CSF drained during acute increases in ICP?
With ventriculostomies
T/F CSF can be drained during aortic aneurysm surgery to improve spinal cord perfusion.
True
What causes increased “brain” volume?
- tumor
- swelling (edema)
What are 3 types of tumors that cause increased “brain” volume?
- meningioma (operable)
- glioblastoma (more invasive)
- pituitary tumor
What are causes of cerebral edema?
- traumatic brain injury
- non-traumatic causes such as ischemic stroke, cancer, or brain inflammation due to meningitis or encephalitis
- vasogenic edema
- the blood brain barrier (BBB) may break down, allowing fluid to accumulate in the brain’s extracellular space
- altered metabolism may cause brain cells to retain water, and dilution of the blood plasma may cause excess water to move into brain cells
Fast travel to high altitude without proper acclimatization can cause ______ ________ _________ ________.
High altitude cerebral edema (HACE)
What is the most rapid and effective means of decreasing tissue water and brain bulk?
Osmotherapy
What is the most popular osmotic agent?
Mannitol
What are two other types of medications used in the acute correction of cerebral edema?
- diuretics: the osmotic effect can be prolonged by the use of loop diuretics (furosemide) after the osmotic agent infusion
- corticosteroids: corticosteroids lower ICP primarily in vasogenic edema because of their beneficial effect on the blood vessel
What are neurologic complications associated with acute hyponatremia attributed to?
Cerebral edema and increased ICP
What is the most common cause of central pontine myelinolysis (CPM)?
Overly rapid correction of low blood sodium levels
What is CMRO2 and CBF?
CMRO2: Cerebral metabolic rate of oxygen
CBF: cerebral blood flow
What is CPP?
Cerebral perfusion pressure
CPP= MAP - ICP or CVP, whichever is greater
How much of CO goes to the brain?
14% of CO
50cc/100g/min
Of the total cerebral blood flow (CBF), how much is cortical and subcortical?
Cortical: 75-80%
Subcortical: 20-25%
Cerebral blood flow is tightly coupled to _______ _________.
Cerebral metabolism (CMRO2)
___________ CMRO2 leads to __________ CBF.
Increased
Increased
T/F brain metabolism requires oxygen and has no significant reserves.
True
What are dangerous levels of cerebral blood flow?
- Less than 30mL/100g/min = ISCHEMIA
- less than 20mL/100g/min = ABNORMAL EEG (INFARCT)
- less than 15mL/100g/min = IRREVERSIBLE DAMAGE
How is cerebral blood flow controlled?
- autoregulation
- CPP
- PaCO2
- H+, HCO3 concentration
- PaO2
- temperature
- neurogenic
With MAP between __________, CBF remains constant.
60-160 mmHg
Loss of autoregulation occurs with:
- acidosis
- hypoxia
- trauma
- volatile anesthetics
What happens if there is a decrease in PaO2, while the PaCO2 remains normal?
CBF is unaffected
What happens once the PaO2 drops below 50mmHg?
There is an increase in CBF, even in the presence of hypocapnia
An increase in PaO2 within the normal range results in:
Only a slight increase in cerebral vascular resistance or vasoconstriction
What is a potent determinant of CBF?
Arterial CO2 tension (PaCO2)
Within physiologic range, what type of relationship with PaCO2 does CBF have?
An approximately linear relationship
PaCO2 is a potent _________ ___________.
Cerebral vasodilator
How much does CBF change for each 1mmHg change in PaCO2?
~ 4% for each 1mmHg change in PaCO2
Decreased pH (acidosis) causes what to happen to CBF?
Increased CBF (vasodilation)
Increased pH (alkalosis) causes what to happen to CBF?
Decreased CBF (vasoconstriction)
What is the cerebral metabolic rate of oxygen?
3.5cc/100g/min
Cerebral blood flow and ________ _______ _______ are coupled in the absence of pathology and/or various anesthetic drugs.
Cerebral metabolic rate
What do volatile agents do to CBF and CMRO2?
Dose dependent increase in CBF, due to vasodilation, with a dose dependent decrease in CMRO2. (Uncoupled CBF and CMRO2)
Nitrous oxide leads to __________ CBF and ___________ CMRO2.
Increased
Increased
When body temperature decreases, what happens to CBF?
It decreases also
How much does CBF change per ˚C in core body temperature?
7% per 1˚C
T/F hypothermia decreases both CBF and CMRO2.
True
At what temperature does the EEG become isoelectric?
20˚C
Does hyperthermia increase or decrease CBF and CMRO2?
Increases both
How much will CMRO2 decrease with an 8˚C temperature decrease?
50%
What do IV anesthetics do to CBF and CMRO2?
Decrease both
What does ketamine do to CBF and CMRO2?
Increases both
What affect do opioids have on CBF and CMRO2?
No affect on CBF and minimal effects on CMRO2
What affect to benzos have on CBF and CMRO2?
Minimal change in CBF with reduction in CMRO2
With an intact BBB, what effect do alpha and beta agonists and antagonists have on CBF?
No effect with the BBB intact
Do SNP, NTG, and trimethephan increase CBF?
Yes, vasodilators all increase CBF
What effect do non-depolarizing NMBDs have on CBF or CMRO2?
No significant effect on CBF or CMRO2
What does succinylcholine do to CBF/CMRO2?
Controversial, text books say that it leads to increased CBF and CMRO2 due to increased spindle activity,however, studies have shown this is not clinical significant
