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Global Cerebral blood flow
Cortical Cerebral blood flow
(mostly gray matter)
80% of CBF
Subcortical Cerebral Blood Flow
(mostly white matter)
20% of CBF
Cerebral blood flow takes what percentage of the CO?
Cerebral Metabolic Rate
Cerebral vascular resistance
1.5 to 2.1 mm Hg/100g/min/mL
Cerebral venous PO2
32 to 44 mm Hg
Cerebral venous SO2
55 to 70%
ICP while supine
8-12 mm Hg
What percentage of the brain's energy consumption is dedicated to support electrophysiological function?
40% of the brain's energy consumption is dedicated to what?
Cellular homeostatic Activities
Local CBF and CMR are _________ and are approximately _______ times greater in gray matter than in white matter
CBF and CMR are heterogeneous and are 4 times more active in gray matter than white
- 1. provide structural lattice framework
- 2. reuptake of neurotransmitters
- 3. delivery and removal of waste
- 4. BBB
What are the chemical/metabolic/humoral factors influencing Cerebral Blood Flow?
- CMR- anesthetics, temp, seizures/arousal
- Vasoactive Drugs- anesthetics, vasodilators, vasopressors
What are the myogenic factors influencing cerebral blood flow?
What are the neurogenic factors influencing cerebral blood flow?
Extra-cranial SNS and PNS pathways
What percentage of decrease in CMR occurs with each degree (Celsius) of temperature reduction?
Temperature is different from anesthetic EEG suppression because
Temperature can suppress not only the CMR associated with neuronal function (60%) but also homeostatic function (40%)
At what temperature does a toxic effect occur as a result of protein denaturation?
42 degrees Celsius
At what temperature does complete suppression of the EEG occur?
18-20 degrees Celsius
Cerebral blood flow increases rapidly when PaO2 drops below what value?
60 mm Hg
What mediates the response to hypoxia in the brain?
- Vasodilation occurs (maybe) by:
- NO release
- hypoxia-induced hyperpolarization of vascular smooth muscle via APT dep. K channels
- Rostral ventrolateral medulla stimulation
What is the rate of change in CBF in relation to changes in PaCO2?
For every 1 mm Hg change in PaCO2, the CBF correspondingly changes 1 to 2 mL/100g/min
This change rate is reduced when the PaCO2 drops below 25 mm Hg, meaning the CBF does not change at the above rate when the PaCO2 is below 25 mm Hg
How do anesthetic drugs alter CBF changes related to PaCO2 levels?
Anesthetic drugs cause a greater reduction in CBF when hypocapnia occurs compared to how the brain reacts when no anesthetic is in the system.
Autoregulation occurs between MAP values of
70 to 150 mm Hg
What does a MAP of 70 correspond with (hint: what CPP value?)
MAP 70 mm Hg --> CPP 55-60 mm Hg
What is the single most important determinant of blood viscosity?
In patients with focal ischemic stroke, manipulation of the HCT when it is above ___ is the only time when manipulation of the HCT is useful to reduce ischemic injury.
Dexmedatomidine reduces the CBF the most in what intracranial vessel?
With respect to ICP, is CBF or CBV the most critical variable?
Cerebral Blood Volume
Normal Brain Cerebral Blood Volume:
5 ml/100 g of brain
What is the relationship of change between PaCO2 and Cerebral Blood Volume?
CBV changes about 0.049 mL/100 g for each 1 mm Hg change in PaCO2
So, the CBV can change about 20 ml for a range of 25- 55 mm Hg PaCO2
Recite the volatile anesthetics in order of vasodilating potency from the most potent to the least
What receptor type and channel type does Xenon exert it's anesthetic properties with?
NMDA receptors and TREK 2-pore K channels
What areas of the brain do not exhibit the tight 8 angstrom barrier like the majority of the BBB?
- Area postrema
Which anesthetic drugs are safe to use in known epileptic patients?
Isoflurane and propofol
Etomidate is not epileptogenic, unless it is used in epileptic patients
What drugs are known to be epileptogenic?
What is the dose of mannitol for increased ICP?
0.25 to 1 gram/kg
What are the side effects associated with glucocorticoid administration?
- GI bleeding
- electrolyte abnormalities
- increased incidence of infection
What is the equation to calculate MAP?
What is the Cerebral flow of CSF?
- Lateral ventricles -> Foramen of Monroe->
- 3rd ventricle -> aqueduct of Sylvius ->
- 4th ventricle -> foramen of Magentie/Luscka ->
- Subarachnoid space to dural sinus to superior sagittal vein (arachnoid villi) to internal jugular
what direction does the autoregulation curve shift in chronic HTN?
To the right
- Takes into consideration ICP effects.
- Normal is 50-100 mm Hg
What law does CPP utilize?
Flow thru a rigid vessel
What is the ganglion group that influences SNS innervation of cerebral vessels?
Superior cervical ganglion
What is the ganglion group that influences PNS innervation of the cerebral vessels?
What does blocking the stellate ganglion do?
Increases cerebral blood flow because decrease in SNS tone
Decreasing the HCT
increases cerebral blood flow
Increasing the HCT
decreases cerebral blood flow
Name 5 drugs that act as cerebral vasodilators?
- 1. NTG
- 2. Nitroprusside
- 3. CCBs
- 4. Adenosine
- 5. Hydralazine
Describe the effects of the alpha1 agonists on CBF
- neosynephrine has no effect on CBF
- norepinephrine increases CBF (because of it's B1 activity)
How do small and large doses of epinephrine (B agonist) affect CBF?
small doses increase MAP, while large doses increases MAP, CBF, and CMRO2 by about 20%
What happens if the BBB is compromised and a beta agonist is given?
The effects will be exaggerated, i.e. the CMRO2 and CBF will increase
What effects do beta-blockers have on patients with intracranial pathology?
The effects are secondary to the changes in perfusion pressure. There are no direct effects from beta-blockers on the cerebral vasculature
What happens in the brain when dopamine is administered?
Not much. The increases in CMRO2 are minimal, and vasoconstriction is absent.
Dobutamine administration in the neuro patient is
not a good idea. Dobutamine increases both CMRO2 and CBF
What the heck is fenoldapam?
It is a dopamine agonist with action at the DA1 and alpha 2 receptors.
It causes systemic hypotension and reduces CBF (alpha 2)
What effect does precedex have on the brain, and what is it's category?
Alpha 2 agonist
Decreases MCA flow by 25% in dose dependent manner
Not sure if its direct vasoconstriction or reduction in CMRO2
If the relationship between CBF and CBV are not 1:1, then what is it?
For a 50% increase in CBF, a 20% increase in CBV results
When I say Morphine, you say
No effect on CBF or cerebral autoregulation.
There is a decrease in CMRO2 b/c histamine release
Fentanyl and sufentanyl
Fentanyl causes a mod. global reduction in CBF and CMRO2
Sufentanyl cause a reduction or no change in CBF and CMRO2`
Remifentanil is different because
- Small doses can increase CBF and
Large doses can decrease CBF
If you're giving flumazenil to wake up a verseded patient, be cautious because
Increased CMRO2, CBF, and ICP will occur, especially in head injured patients whom had poor ICP control
What is the appropriate bolus dose of lidocaine to administer to the neuro patient?
1.5 to 1 mg/kg
What is the MAC level that maximum CMR reduction occurs (eeg suppression)?
MAC 1.5 to 2.0
What MAC results in vasodilation and increases in CBF that override decreases via decreased CMRO2?
Which is not preserved during anesthesia with volatile anesthetics?
A) CO2 responsiveness
B) autoregulation is not preserved when at the upper end of the curve (150mmHg)
What is the metabolite of atracurium that might be epileptogenic?
What INH agents affect CSF absorption?
Halothane and enflurane decrease absorption
Isoflurane increases absorption
What INH agents affect CSF secretion?
Halothane decreases secretion
Enflurane and desflurane increases secretion
What INH agents have no effects on CSF absorption or secretion?
Isoflurane has no effect on secretion
Desflurane has no effect on adsorption
How tight are the epithelial cells of the BBB?
fenenstrated capillary beds in the rest of the body are 65 angstroms
What area do seizures originate from when induced with brevital?
What areas do seizures originate from when induced with ketamine?
Limbic and thalamic areas
What can happen if glucocorticoid steroids are given to a patient that does not have a mass-lesion?
Pseudotumor cerebri with an increase in ICP and papilledema