Neuro Flashcards
Between what PaCO2 pressures is CBF directly related?
20-80mmHg
How much does CBF change per 1mmHg PaCO2?
1-2mL/100g/min
How much does CBF change per degree celcius?
5-7%
How cool is a patient kept during CPB?
30-32* C
What kind of drugs can cross the BBB?
small, lipophilic, uncharged
What causes rupture of cerebral aneurysm?
rapid changes in pressure (up or down)
List contents and percentages of the cranial vault
brain 80%, blood 12%, CSF 8%
What are two equations for CPP?
MAP - ICP (or CVP)
What’s an ideal CPP?
60-70mmHg
Which IV induction drugs increase CMRO2?
ketamine
Which IV induction drugs increase CBF?
none
Which volatile can cause isoelectric EEG?
isoflurane (think isoelectric)
Hypertonicity of blood causes movement of H2O into/out of brain
out of
Describe the relationship between PaO2 and CBF
CBF is 50ml/100g/min for all PaO2 values above 50mmHg
What is total CSF volume?
~150cc
How long does hypercapnia/hypocapnia effect the brain? Why?
~24hr; CO2 crosses the BBB and HCO3- does not until about 24hr
Severe hypoxemia would have what effect on CBF?
hypoxemia causes a drastic increase in CBF after PaO2 drops below 50mmHg
What is the most important determinant of blood viscosity? how does it affect CBF?
hematocrit; decreased viscosity increases CBF (though decreases ability to deliver oxygen to cells)
Optimal cerebral O2 delivery occurs at a Hct of ___.
~30%
Why does mannitol cause a transient increase in CBF?
It causes an increase in circulating blood volume from other cells of the body
What are the advantages/disadvantages of mannitol vs lasix?
mannitol decreases brain water volume (lasix does not); mannitol causes a transient increase in ICP as water from other cells enters the systemic circulation (lasix does not)
Which IV induction agents are capable of producing burst suppression?
barbs, etomidate, propofol
Which IV induction agents can cause EEG electrical silence at high doses?
barbs, etomidate, propofol
Which volatile can produce burst suppression and at what MAC?
des (>1.2MAC), sevo (>1.5MAC)
Which test assesses which part of the spinal cord: anterior/posterior, SSEP/MEP
anterior - MEP, posterior - SSEP
Spinal cord perfusion is best assessed with which test? why?
MEP; because it assesses the anterior portion of the spinal cord (where the supplying arteries are located)
Which type of evoked potential is most affected by anesthetic agents?
visual evoked potential
Which type of evoked potential is not affected by anesthetic agents?
brain stem auditory evoked potentials
Opioids have what effect on EEG?
depression
How do you treat cerebral vasospasm?
“triple H” - hemodilute ~30% Hct, HTN 160-180mmHg systolic, hypervolume 12-14 CVP
What is the advantage of electric silence in the brain? what is the limitation?
electrical silence eliminates the metabolic cost of electrical activity (~60% of overall O2 consumption), however it has no effect on basal energy requirements
Among the drugs that cause electrical silence, why are barbs preferred?
they affect all areas of the brain equally
The brain consumes what percent of total body O2?
20%
At what CBF is cell function deranged?
<10ml/100g/min
Vasopressors have what effect on CBF?
none, unless MAP was below 50-60mmHg or above 150-160mmHg
Why is lidocaine used in neuro as an anesthetic adjunct?
it decreases CBF (by increasing CVR) without any other significant hemodynamic effects
What are the effects of barbs on the CNS?
sedation, depression of CMRO2, reduction of CBF (due to increased CVR), anticonvulsant activity
When might a venous air embolism occur?
whenever the wound is above the heart (pressure in vein is sub-atmospheric)
CBF is autoregulated between what MAPs?
60-160mmHg
What could be the effect of MAP above 160mmHg?
cerebral edema, hemorrhage
What is a normal ICP?
10mmHg or less
What is “luxury perfusion?” What is circulatory steal phenomenon?
Luxury perfusion is the decreased CMRO2 combined with increased CBF (O2 supply) seen with volatiles. Circulatory steal is when vasodilation only effects non-ischemic areas (ischemic areas are already maximally dilated), and results in a redistribution of blood flow to non-ischemic areas.
Opioids have what effect on CMRO2 and ICP?
minimal, unless PaCO2 rises secondary to respiratory depression
What is Cushing’s Triad?
Hypertension, bradycardia, irregular breathing (signs of dangerously high ICP)
What ICP would be considered elevated?
sustained P over 15
What is the equation for CBF?
CBF = CPP/CVR
Describe where you might find a cerebral aneurysm?
usually seen around the circle of Willis, most commonly at bifurcations (anterior communicating 30%, posterior communicating 25%, middle cerebral 20%)
What typically triggers a breath, hypoxia or hypercapnia?
Hypercapnia
