Neuroanatomy (exam 1) Flashcards
The brain receives what % of cardiac output?
15%
The brain receives how many ml of blood per 100 g of brain tissue per min?
50-65 mL
Does hypothermia increase or decrease CBF?
Decreases CBF
Does hyperthermia increase or decrease CBF?
Increases CBF
Does CBF increase or decrease with age?
Decreases with old age
What is the most powerful factor to increase CBF?
CO2
True or False: A doubling of CO2 doubles CBF?
True
HTN causes a right or left shift of the autoregulation curve?
Rightward shift
Metabolically what occurs so that CO2 can cause an increase in CBF?
CO2 combines with water to form carbonic acid which forms Hydrogen.
The H-‘s are what cause vasodilation of cerebral vessels (causing an increase in CBF)
The Brain uses O2 at a near constant rate, if CBF becomes insufficient to supply the needed amount of O2 what happens?
vasodilation occurs and CBF increases (known as autoregulation)
Both CO2 and O2 can cause an increase in CBF but which one is the most powerful factor?
CO2 is the most powerful factor.
O2 as hypoxia is a potent stimulus.
The cerebral blood flow is maintained fairly stable for a MABP of ?
50-150 (60-160)
autoregulation shifts to the left with what perfusion problems?
hypoperfusion / cerebral ischemia
autoregulation shift s to the right with what problem?
chronic HTN
*Arteries that form the circle of Willis?
2 carotid and 2 vertebral arteries - which merge to form the Circle of Willis at base of brain.
Three major components of the Intracranial contents?
Brain
CSF
Blood
What are astrocytes and their function?
star-shaped non-neuronal cells that support and protect neurons as well as provide nutrition.
Electrical stimulation of excitatory glutaminergic neurons leads to?
increase in intracellular calcium ion and vasodilation of nearby arterioles.
Does arterial or venous BP fluctuate greatly?
arterial
People with hypoperfusion/ cerebral ischemia, autoregulation is shifted to the left or right?
left
Autoregulation by 2 separate mechanisms, what are the two mechanisms?
Responses to mean blood pressure changes
Responses to pulsatile pressure (perfusion pressure– for example…decreased during CPB)
When MAP rises acutely during strenuous exercise what happens so that vascular hemorrhage does not occur?
SNS constricts the large and intermediate-sized brain arteries enough to prevent the high pressure from reaching the smaller brain blood vessels. Thus, preventing vascular hemorrhages.
Give me an example of global ischemia and focal ischemia?
Global = cardiac arrest Focal = localized stroke
What is Penumbra?
an area of moderate ischemia peripheral to an area of greater ischemia, the penumbra area has compromised blood flow.
(immediate revascularization can save neurons in the penumbra)
most sensitive area of the brain for hypoxia/ischemia?
hippocampus (area for recent memories)
What is tPA used for?
window of use?
contraindications?
risk/side effects?
clot buster, reperfusion of an ischemic area of the brain.
3 hour window of use.
contraindications: hemorrhagic stroke, recent surgery.
Risks/side effects: cerebral hemorrhage
target glucose for treatment of cerebral ischemia?
target 180 mg/dl
Treatments for epilepsy?
Benzodiazepine
Barbiturates
Anti-epileptic (phenytoin)
What are most strokes caused by?
arteriosclerotic plaques that occur in one or more of the feeder arteries to the brain.
Most common arteries affected by Hemorrhagic strokes?
Middle Cerebral Artery
Posterior Cerebral Artery
Midbrain arteries
Entire capacity of cerebral cavity enclosing brain and spinal cord is about how much in mL?
1600-1700mL
CSF alone is how many mL?
150mL
Rate of CSF formation is about how much per day?
500-600mL/day
What is Coup, Contrecoup, and coup contrecoup?
Coup = contusion on the same side as the impact injury.
Contrecoup = injury to the opposite side as the site of injury.
Coup contrecoup = injury at the site of trauma and the opposite side of the brain.
What structure is responsible for drainage or reabsorption of CSF?
Arachnoid Villi
Normal CSF pressure in children is?
Adults?
children = 3-7.5 adult = 4.5-13.5
Just need to know that children is less than adults.
What is normal ICP?
less than or equal to 20
What is the main cause of death after head injury?
Elevated ICP
Intracranial pressure curve, what does point 3 and 4 tell you?
At point 3, focal ischemia occurs.
At point 4, global ischemia occur
Sustained elevation of ICP leads to?
brain herniation
Normally increases in volume (ICP) are initially well compensated, what points on the Intracranial pressure curve would this be?
1 and 2
*What is Cushings Triad?
increase ICP leads to reflex increase in MAP (hypertension), decrease in HR (bradycardia) and irregular respiration.
Intracranial Hypertension would be defined as?
ICP greater than 20 mmHg
What are some causes of intracranial hypertension?
mass lesion
hematoma
head trauma
herniation of the brain due to increased ICP will occur through what two structures?
tentorial notch
foramen magnum
Intracranial hypertension will cause what to occur on the same side of the mass?
cranial nerve three compression on the ipsilateral side = fixed dilated pupil to the same side as the mass (also cushings triad)
Chronic intracranial hypertension will cause?
papilledema
Treatment of intracrainial hypertension?
ABCs
Intubation plus hyperventilation
Maintain PCO2 level 25-30ish mmHg
Mannitol
Sedation
Steroids
Slowly wean from ventilator
Glasgow coma score, tell me what each number range means?
Glasgow coma score < 7
Severe brain injury defined as < 8-9
Moderate injury = 8-12
Minor injury = > 13
can’t ever have a ZERO
Two techniques to monitor ICP today? (explain)
1…intraventricular (requires cannulation of ventricular frontal horn)
2…intraparenchymal (often held in place by bolt screw)
An increase in ICP can reduce what?
CBF
Cerebral blood flow and BP is maintained pretty constant over a wide MABP, what would that range be?
50-150
What does CPP measure?
Cerebral Perfusion Pressure (CPP)- Is actually what is measured as a surrogate for Cerebral Blood flow under conditions where stats are rapidly changing (i.e. ill person with increased ICP and possible herniation in progress)….
What measurement is the difference between MAP and the greater of ICP or CVP?
CPP
equation for CPP is?
MABP - ICP or CVP (whichever is greater)
What should the CPP range be, and what do the ranges mean?
CPP Goal- Maintain above 50-55
CPP < 40 considered critical
Difference between communication and non-communicating Hydrocephalus?
Communicating: Caused by blockage of fluid flow around base of brain or by blockage of arachnoidal villi
Fluid collects on the outside of brain and some collects inside the ventricles
Non-Communicating:Caused by block in aqueduct of Sylvius
Volumes of lateral and 3rd ventricle increase greatly
BBB is permeable to?
Water
CO2
O2
Most lipid-soluble substances
BBB is slightly permeable to?
Electrolytes: Na+, Cl, K+
BBB is impermeable to?
Plasma proteins
Non-lipid-soluble large molecules
What can cause the BBB to be more permeable? (like a break in the barrier)
Microwaves Radiation Trauma Hypertension Infection
What typically causes Brain Edema?
Usual cause is increased capillary pressure or damage to capillary wall that makes the wall leaky to fluid.
Starts a vicious cycle: edema decreases blood flow, causing ischemia, then more edema
Most of the Brains energy is supplied as what? and how long will that supply last?
Glucose
only a 2 minute supply of glucose stored as glycogen in the neurons.
Most common first degree brain tumor is?
Astrocytoma
Do first degree brain tumors commonly or rarely undergo metastasis?
rarely
What type of prognosis and expectancy does astrocytoma have?
grave prognosis and less than 1 year life expectancy.
2nd most common first degree brain tumor? (arise from arachnoid cells external to the brain, slow growing)
Meningioma
Tumor found in the 4th ventricle, can cause hydrocephalus, poor prognosis?
Ependymoma
tumor that is relatively rare and slow growing?
oligondendroglioma
Most common prolactinoma, causes tunnel vision, hyper or hypo pitutarism can result?
Pituitary adenoma
3rd most common first degree tumor with schwann cell origin?
Schwannoma
What nerve is an acoustic schwannoma tumor localized to?
VIII nerve
What test is diagnostic for seizures?
EEG
What type of seizure does not cause a loss of consciousness?
Focal (partial) seizure arise from discrete region, no loss of consciousness
causes of tumors in children, adults, and elderly?
Children- genetic, infection (febrile), trauma, congenital, metabolic
Adults- tumors, trauma, stroke, infection
Elderly- stroke, tumor, trauma, metabolic, infection
What is the major goal in neurosurgical anesthesia?
to provide adequate tissue perfusion to brain and spinal cord so that regional metabolic demand is met and to provide adequate surgical conditions (“a relaxed brain”)
In general IV anesthetics do what to CMR and CBF
where most inhalation anesthetics cause what change to CMR and CBF?
IV anesthetics decrease cerebral metabolic rate (CMR) and CBF in parallel fashion….
Most inhalational anesthetics decrease CMR with an increase in CBF (cerebral vasodilation)
What CANNOT not be recommended in patients who have experienced stroke?
hyperventilation
Hypercapnia is what?
high CO2
what is hypocapnia?
low CO2
what CO2 concentration can dilate vessels in the normal area of the brain but not in the damaged (ischemic) area?
high or hypercapnic
what is intracerebral steal?
“stealing from the poor”
Hypercapnia -
when blood flow is shunted away from an ischemic area to a normal blood flow area of the brain.
what CO2 concentration can divert blood flow from the normal area of the brain to an ischemic area?
low or hypocapnic
what is “reverse” cerebral steal/Robin hood effect?
“stealing from the rich to give to the poor”
when blood is diverted from a normal area of the brain to an ischemic area.
Hypocapnia (low CO2)
How can you induce the “steal” phenomena?
pharmacologically with anesthesia (not hyperventilation)
Anesthesia alters ICP through changes in what?
CBV (which appear to be proportional to changes in CBF, thus in ICP)
Intracerebral steal VS. reverse steal?
intracerebral = blood flow away from ischemic area.
reverse = blood flow to ischemic area
How are the smaller blood vessels in the brain protected when MAP rises acutely? (ultimately protecting against vascular hemorrhage)
SNS constricts the large and intermediate-sized brain arteries enough to prevent the high pressure from reaching the smaller brain blood vessels. Thus, preventing vascular hemorrhages.
Sensory CN are?
I olfactory, II optic, VIII vestibulocholear
Motor CN are?
III occulomotor, IV trochlear, VI abducen, XI accessory, XII hypoglasal
What 4 large arteries merge to form the circle of Willis?
2 carotid and 2 vertebral arteries.
—— is the basic functional cell of the CNS?
Neuron
Sensory or Motor neuron has multiple dendritic processes and constitutes the majority of the CNS.
Motor
What cell lines the roof of the 3rd and 4th ventricles of the brain and central spinal cord. They also form the choroid plexus which secretes CSF?
Ependymal cells
These cells develop into large macrophages that phagocytize neuronal debris?
Microglia cells
Forms the myelin sheath of axons in the brain and spinal cord and are capable of mylenating more than one axon?
Oligodendrocyte cells
This cell forms the myelin sheath of peripheral nerves?
Schwann cells
electrical stimulation of excitatory glutaminergic neurons leads to increase in ?
intracellular calcium ion and vasodilation of nearby arterioles.
Rate of CSF formation is constant, this makes what really important?
This makes drainage or reabsorption by arachnoid villi important!
blockage of CSF drainage or reabsorption by the arachnoid villi can be caused by?
tumor
hemorrhage
infection
what are the three signs of cushing’s triad?
- Irregular respiration
- Bradycardia
- hypertension
VAE is most often associated with what procedure?
posterior fossa procedures in the sitting position.
Intraoperative goals if a patient is suspected to have or does have a venous air embolism?
- inform the surgeon immediately.
- discontinue nitrous, increase 02 flows.
- modify the anesthetic.
- Have the surgeon fluid the surgical field.
- provide jugular vein compression
- aspirate the right atrial catheter.
- provide cardiovascular support.
- change the patients position.
most sensitive / noninvasive for VAE?
TEE
*Onset of insult when monitoring with evoked potentials would look like what?
decrease in amplitude and
increases in latency
When an evoked potential changes what must you do?
you must assess the physiologic, anesthetic, and surgical environment to determine what has contributed to the change.
*What does diffuse ischemia look like when monitoring evoked potentials?
What does mechanical injury or localized ischemia look like?
slow loss of response amplitude with an increase in latency = diffuse ischemia
fast losses of amplitude with minimal latency changes = mechanical injury or localized edema.
Medication commonly used for evoked potentials is opioids, why?
cause only mild depression of all responses
volatile anesthetics and N20 produces what kind of evoked potential changes?
decrease in amplitude and increase in latency
most commonly monitored evoked potential is?
SSEP
What evoked potential is used during CEA?
Cortical SSEP
What medication is acceptable to use with SSEP but not ok to use with MEP?
NMB are acceptable with SSEP
A change in SSEP corticol amplitude is most sensitive indication of what?
ischemia
SSEP can be used to monitor ischemia from what all factors?
VASOSPASM retractor pressure hypotension clipping hyperventilation
If SSEP is used during spinal cord surgery what can it identify?
mechanical or ischemic insult when they result in alteration or loss of transition through surgical field.
What evoked potential is used extensively for monitoring during surgery involving posterior fossa?
ABR (auditory brainstem responses)
When are visual evoked potentials used?
during craniofacial procedures,
pituitary surgery, and surgery in the
retrochiasmatic visual tracts and occiptal cortex.
(considered less useful in surgery)
What evoked potential is very common in spinal surgery?
MEPs bc it has a very good correlation with post-op outcome.
50-80% reduction in morbidity
Preferred form of anesthetic delivery when using MEP?
TIVA is preferred
(propofol with or without ketamine in combination with opioids) discuss with surgeon.
Name the CN 1-12
1 olfactory 2 optic 3 oculomotor 4 trochlear 5 trigeminal 6 abducens 7 facial 8 auditory 9 glossopharyngeal 10 vagus 11 spinal accessory 12 hypoglossal
Most common CN monitored during surgery is?
Facial nerve (CN 7)
Orbicularis oculi and/or orbicularis oris muscles
stimulation of what two CN will cause CV changes?
CN IX and X
stimulation of this CN can cause potentially harmful head movement (sternocleidomastoid and trapezius activation)
CN XI
What CN monitoring is becoming common in skull base and anterior neck procedures?
X vagus nerve
Best choice muscle relaxant (during induction) for head injury with HTN and disturbed autoregulation?
Nondepolarizing neuromuscular relaxants do not appear to have clinically significant direct effects on CBF or CMRO2, provided MAP is not altered after administration
Rocuronium 1 mg/kg
How do IV anesthetics change CMR and CBF?
IV anesthetics decrease cerebral metabolic rate (CMR) and CBF in parallel fashion
How do inhalational anesthetics change CMR and CBF?
most inhalationals decrease CMR with an increase in CBF (cerebral vasodilation)
How do anesthetic agents change the affect of ICP?
by changing the rate of production and reabsorption of CSF/
Hyperventilation and head trauma, what is correct and incorrect?
Hyperventilation can rapidly control intracranial HTN, but prolonged and extreme hypocapnia (low CO2) from hyperventilation can result in a marked decrease in CBF in pts with head trauma (another reason it is C/I in CVA).
Only short duration of mild to moderate hyperventilation (hypocapnia) should be initiated (other pharmacologic/surgical intervention should be performed to control critical intracranial HTN)
“BEST” inhaled anesthetic for NEURO patients would be?
Isoflorane
cerebral vasodilators (capable of increasing ICP) usually depress metabolism EXCEPT for
N20
Why does N20 have restricted use in neurosurgical procedures?
N/V incidence among other properties
When N20 is added to volatile anesthetics it increases both what and what?
CBF and CMR
What gas has no direct vasodilating effect as well as the most dramatic increase in CBF and ICP when administered alone?
N20
Other name for Isoflurane?
Forane
What has Isoflurane been reported to do to whole brain metabolism?
reduce whole brain metabolism by half.
potent cerebral metabolic depressive effects.
Which gas has the only property to increase ICP mildly but can be prevented with hypocapnia?
Isoflurane
Which gas has the disadvantage of compound A renal toxicity?
Sevoflurane
What is the other name for Sevo?
Ultane
What surgical situation can make sevo undesirable to use?
prolonged anesthesia for neurosurgery with preexisting renal disease.
Which two gases may have neuro-protective effects similary to Iso? One is proven clinically and one is not…
proven clinically = Des
not proven clinically = Sevo
Why is ketamine a unique IV anesthetic?
increases both CBF and CMR while all other IV anesthetics decrease both.
(synthetic opioids are a possible exception, may slightly increase ICP)
what IV anesthetic has the effect to keep ICP the same or slightly increase?
synthetic opioids
True or False
IV anesthetics decrease CBF and CMR due to vasoconstriction?
False, - Decrease in CBF by most is a result of reduced cerebral metabolism secondary to cerebral functional depression… not due to vasoconstriction
Does etomidate have CV side effects, does it change CMRO2, and what are it’s adverse effects?
does not have CV side effects.
decreases CMRO2 like barbs
Adverse effects: adrenocortical suppression & frequent occurrence of involuntary muscle activity and seizure activity – use with great caution with pt having history of seizures
Should propofol be used in children?
Prolonged use may cause systemic acidosis and progressive cardiac failure and even death in children…use of prolonged infusion in children is UNJUSTIFIED
Propofol has dose related decreases in what and what?
It also decreases what else?
dose related decreases in CBF and CMR02.
Also decreases ICP
What all does ketamine increase?
increases CBF, CMRO2, and ICP.
the markedly increase in ICP by ketamine can be blocked or attenuated by what?
induced hypocapnia, thiopental, or benzos
What does Versed do to ICP?
decrease or no change to ICP
Which is better at maintaining hemodynamic stability, versed or thipental?
Versed
Flumazenil and pts with impaired intracranial compliance?
Flumazenil (antagonist) also antagonizes effects of benzo of CBF, CMRO2, and ICP – use cautiously when reversing sedation in pts with impaired intracranial compliance
What opioid is used in neurosurgery with satisfactory results more so than any other?
Remifentanil which is fast on and fast off.
alfentanil can also be used over fentanyl and sufentanil
Succinylcholine and use with neuro patients?
elevates ICP, may be prevented or decreased with pretreatment with NDMR.
Induced hyperkalemia is another concern with neuro patients and Sch. use
cytotoxic brain swelling
shift of fluid from extracellular to intracellular space
o Cytotoxic (intracellular) edema- fluid accumulating within cells as a result of injury, usually from toxicity, ischemia or hypoxia
vasogenic brain swelling
shift of fluid from intravascular to extracellular space
o Vasogenic- brain metastases, abscesses, trauma, hemorrhage (develops as a result of a physical disruption of the vascular endothelium or functional alterations in endothelial tight junctions
vasogenic brain swelling is most commonly incolves
involves the white matter
Interstitial brain swelling
shift for CSF into extracellular space
o Interstitial edema- CSF migration into the periventricular white matter, commonly due to conditions that impede CSF circulation, absorption or both
when observed in extra axial spaces, the most likely cause of intracranial hemorrhage is
trauma
name the three types of brain herniation:
- ) subfalcine
- ) transtentorial
- tonsillar
If presented with a patient with s/s of cushings triad, what type of herniation is most likely the cause?
Tonsillar
features inferior displacement of the cerebral tonsils through the foramen magnum into the cervical spinal canal… results in compression of the medulla, producing dysfunction of respiratory and cardiac rhythm centers
occurs when a hemispheric mass pushes the cingulate or supracingulate gyri beneath the falx (easily recognized on CT or MRI from deviation of falx and extension of hemispheric structures across midline
subfalcine herniation
occurs when a mass on either side of the tentorium causes brain herniation through the tentorial incisura (descending or ascending)
Transtentorial-
features inferior displacement of the cerebral tonsils through the foramen magnum into the cervical spinal canal… results in compression of the medulla, producing dysfunction of respiratory and cardiac rhythm centers
tonsillar
this type of hydrocephalus results from excessive CSF production by choroid plexus tumors or from obstruction to CSF absorption by arachnoid villi which may be caused by SAH/meningitis
communicating
*elevated pressures, CSF may leak from ventricles into brain interstitial edema
this type of hydrocephalus results secondary to obstruction along the CSF pathway b/w the lateral ventricles an the fourth ventricular outlet
obstructive
Preferred imaging modality for initial assessment of TBI
CT
shows greater sensitivity than CT for detection is subtle lesions & better suited for evaluation of subacute and chronic TBI (unexplained neurologic deficit that cannot be explained by CT)
this technique is also superior to CT in detecting axonal injury, small areas of contusion, and some lesions in brainstem, basal ganglia, and thalami
MRI
diffuse axonal injuries (DIAs) are
shear injuries
related to primary TBI lesions
Major contributors to secondary TBI:
Hypotension Hypoxemia Hypolycemia Hypocarbia / Hypercarbia Hyperglycemia
SAH-non-contrast CT primary screening tool, however, THIS is gold standard for detection of intracranial aneurysm- also represent tx. modality b/c it permits coiling of aneurysm and endovascular tx. of vasospasm
DSA
for aan AVM what is the gold standard for imaging evaluation?
DSA
EMG responses are resistant to effects of ____ except ____.
resistant to: anesthesia
except: NMB
Common “relative” contraindications for MEPs are:
epilepsy, cortex lesion, skull defects, high intracranial pressure, intracranial apparatus (electrodes, vascular clips, shunts), cardiac pacemakers, and implanted pumps
during monitoring of EPs Hypothermia can mimic :
latency & amplitude changes:
surgical change
-increased latency & decreased amplitude
during monitoring of EPs Volatile anesthetics produces what changes to latency & amplitude?
increases latency and decrease in amplitude
during monitoring of EPs, N2O produces what changes to latency & amplitude?
increased latency and decreased amplitude
patients who are at risk for an ischemic event should not be infused with what type of solutions?
why?
Dextrose solutions
-Hyperglycemia should be avoided in pts at risk for an ischemic event.
Tight glucose control can increase risk of hypoglycemia which could be harmful to pt - discuss with the surgeon
during a craniotomy, what solutions are generally avoided?
hypo-osmolar and dextrose containing solutions
Ideally, IV fluid should be administered at rate to maintain CO but avoid
excessive fluid resuscitation
during infusion of mannitol, ICP may do what?
increase transiently (vasodilation of cerebral vessels in response to sudden increase to increased osmolarity.)
-then may decrease ICP by movement of water from brain interstitial and intracellular spaces into vasculature –> the end result
o Production of large volumes of dilute urine and normal or elevated plasma osmolality (severe cases 1 liter/hour) is
Diabetes insipidus
type of fluid that should be used to rehydrate a pt with DI?
- 45% NS until euvolemia.
- NS should not be used for initial rehydration b/c of preexisiting hyperosmolar/hypernatremic state
in trauma patient with a head injury; what is the Ideal resuscitation with hypovolemia and ongoing blood loss
fresh whole blood
in a trauma patient or one with a head injury; what fluids are not recommended? why?
Hetastarch and dextran not recommended due to coagulopathy
first choice volume resuscitation of trauma pts with head injuries is
isotonic crystalloid solutions
amount of Na, K , Cl, and Ca found in 1L of NS
Na = 154 meq Cl = 154 meq
amount of Na, K , Cl, and Ca found in 1L of LR
Na = 130meq K = 4 meq Ca = 3 meq Cl = 109 meq
major disadvantage to NS is the possible development of
hyperchloremic acidosis in large volume resuscitation
