Class 5 Deck 1 Flashcards
what are the 3 main components of the intracranial vault?
- CSF (10-15%)
- Brain (80-85%)
- Blood (5-10%)
CSF occupies the _______ space, providing protective layer of fluid between the ______ and the tissue that surrounds it.
- Subarachnoid
- Brain
Where is the CSF produced?
-The choroid plexus of the ventricles
How much CSF is produced per 24hrs?
500cc
How much CSF volume is present at any given time?
-150cc
How does CSF help brain functioning?
- Regulates PH and Electrolytes
- Carries away waste
- Delivers nutrients
What 4 things can increase CSF volumes?
- Choroid plexus mass
- Hyperthermia
- Decreased serum osmolalilty
- Increased CSF osmolality
What 5 things can decrease CSF volume?
- Hypothermia
- Increased hydrostatic pressure
- Increased serum osmolality
- Decreased CSF osmolality
- Diamox
What arteries provide anterior circulation to the brain?
Carotid
What arteries provide posterior circulation to the brain?Where does it enter?
- Verterbral
- Foramen magnum
Venous blood from the brain drains into the venous sinuses, where do these lie and what do they drain into?
- Lie between the layers of the dura
- Drain into internal jugular
What are the characteristics of the brain venous system?
- Sinuses are valveless
- Blood can move back an forth
- Pressure is negative (embolism)
- No SNS influence
- Chemical influenced
The BBB will allow what type of molecules to pass?
- Small
- Lipophilic
- Passive glucose
- Active AA
The BBB prevents passage of what molecules?
- Large
- Charged (ionized)
BBB is disrupted by what?
- HTN
- Hypoxia
- Trauma/Tumors
- Stroke
- Seizures
- Infection
- ↑ Paco2
Blood flow to the brain is tightly coupled to ______ _____.
-Cerebral metabolism
What 4 things will increase cerebral blood flow?
- Stimulation
- Arousal
- Nocoception
- Hyperthermia
What 2 things decrease CBF?
- Sedative/Hypnotic agents
- Hypothermia
What are the dangerous flow of CBF?
-<15 = Irreversible damage
increased CMRO2 leads to _______ CBF
Increased
How is CPP measured?
-MAP-ICP or CVP (what ever is greater)
What is a normal CPP? ICP?
- CPP = 70-100
- ICP = 10-15
Between what MAP range will the brain autoregulate a constant blood flow?
-60-150
In what 4 ways will brain autoregulation be lost?
- Acidosis
- Hypoxia
- Trauma
- Volatile anesthetics
What 3 ways does the brain compensate for ICP?
- CSF regulation
- CBF auto regulation
- Metabolic autoregulation
How is CSF regulated with an increased ICP?
- ↑ CSF absorption
- ↓ CSF Production
ICP refers to pressure where?
-Supratentorial
What is the Monro-Kelly doctrine?
-ICP is stable as long as volume added is balanced by volume displaced. (either blood, brain, or CSF)
What is the limit of the ICP compensatory curve?
-20
What needs to be done with increased ICP?
- Beta blocker
- Tight BP control (A line)
- 0 twitch intubation
- Normothermic (no bair hugger)
What happens to CPP during acidotic states? Alkalotic?
- BF Increase
- BF Decrease
What happens to the brain if it gets too acidotic/alkalotic beyond the limits of compensation?
- Vasodilates w/ increases BF in an attempt to wash out waste.
- Increased blood supply = increases ICP
CBF changes by ___% for each 1mmHg change in PaCo2
4
PaCO2 is a potent cerebral ______?
Vasodilator
CBF is most sensitive to what?
-CO2
If you double CO2, you do what to CBF?
-Double
H+ causes a slow _______ effect in cerebral blood vessels.
Vaso-dilatory
An increase in H+ = what in CBF?
-Increased CBF
Decreased PH = _______ CBF
Increased (acidosis)
Increased PH = ______ CBF.
Decreased (alkalosis)
Once the PaO2 drops below ___ mmHg, hypoxia overrides and cerebral _______ occurs
- 50
- vasodilatation
Cerebral venous O2 is usually ____ mmHg. Reduction below ____ mmHg is necessary to increase CBF
- 35
- 30
How much of the body’s total O2 consumption is used by the brain?
- 15-20%
What is the primary energy source for the brain? and what is needed for the brain to use glucose?
- Glucose
- O2
Increase in Temp = ______ in CBF.
Decrease in Temp = _______ in CBF
- Increase
- Decrease
CBF Δ __% per 1 degree°C change in core body temperature.
7
At what point is the EEG isoelectric?
-20°C
What other factors increase CBF?
- Trendelenburg
- Anemia
What other factors decrease CBF?
- increased Age
- Increased blood viscosity
- PEEP
Most IV agents decrease CBF and CMRO2 except for what?
Ketamine
Etomidate side effect, myoclonis may do what? and what is the larger concern for etomidate?
- Increase ICP
- Adrenal supression
How does narcotics effect CBF, CMRO2 and ICP? and how are they of benefit?
- Minimal to no change
- Block CV effect to intubation and incision
How do depolarizing and non-depolarizing muscle relaxants effect CBF and ICP?
- Succs = Increase in ICP
- Non-depolarizers = no direct effects
What effects does succs have on neuro anesthesia?
-↑ ICP, BP, HR, NorEpi
When is Succs contraindicated in neuro anesthesia?
- Thermal or muscle trauma
- Neurologic deficits
- Prolonged bed rest
Alpha and beta agonists and antagonists have ___ effect on CBF with the ______ intact.
- No
- BBB
Vasodilators will ______ CBF. Espically what 3?
- Increase CBF
- SNP,NTG,Trimethephan
During low dose inhalation anesthesia, CBF is either _______ or slightly ________. Why?
- Unchanged
- Slightly increased
- Vasodilator effect is opposed by a metabolic decrease in flow
Higher doses of inhalational agents have a dominance of the vasodilator effect and cause what?
-Increase in CBF
In general inhalational agents _____ CBF but ______ CMRO2.
- Increase
- Decrease
Sevo at 1 MAC ______ CSF production up to _____%
- Depresses
- 40%
N2O appears to have an __________ effect and should be avoided in cerebral ischemia and elevated ICP cases.
-antineuroprotective
What does N2O do to an air embolism?
-Expand it, worsen outcomes
What syndrome increases local accumulation of metabolic by products? What does this cause?
- Luxury-perfusion syndrome (normocapnia)
- Increased vasodilation and increased flow
Describe cerebral steal syndrome(hypercapnia).
-An ischemic area of the brain will cause increase in PaCO2 to the brain. This increase will take blood away the ischemic portion (can auto regulate), and direct more blood flow to the normal areas.
Describe inverse steal (robin hood) phenomenon. (hypocapnia)
-Hypocapnia will reduce blood flow to normal areas of the brain and redistribute it to ischemic regions.
What type of glial cells have the most tumors?
-Astrocytes (astrocytoma)
