Welliver study guide thingy Flashcards
Describe the flow of CSF through the brain.
produced by the choroid plexus in the 2 lateral ventricles -> through the foramen of Monro into the third ventricle -> through the aqueduct of Sylvius and into the fourth ventricle -> through foramen of Magendi and the 2 foramina of Luschka into the cistern magna -> into the subarachnoid space and spinal column -> absorbed in the subarachnoid space by arachnoid villi of venous system
What is the average CBF?
50 mL / 100 gm / min.
(total 750 mL / min.)
What is luxury perfusion?
perfusion in excess of metabolic needs.
can be beneficial in healthy brains, but may cause “steal phenomenon” in brains which have ischemic areas
What is steal phenomenon?
increased pCO2 or VAA globally “steal” blood flwo from ischemic areas of the brain by causing vasodilatation in healthy areas of the brain. ischemic brain tissue, which already has maximally dilated vessels due to released vasodilator substances, loses luxury perfusion benefit due to global shunting of blood flow.
What is inverse steal, or robin hood phenomenon?
decreased pCO2 constricts normal vessels but not necessarily in ischemic areas due to vasomotor paralysis. this is one rationale for hyperventilating patients with intracranial tumors associated with increased ICP especially when administering VAAs which cause vasodilatation.
What arteries are a part of the Circle of Willis?
How does PaCO2 effect CBF?
linear relationship 1mm Hg increase PaCO2 = 1-2ml /100Gm/min. increase CBF.
How and when does PaO2 effect CBF?
Profound increase in CBF only at PaO2 < 50 mm Hg
How do you calculate CPP?
CPP = MAP-ICP or CVP whichever is higher
What is normal CPP?
100 mmHg
What occurs when CPP is < 50 mmHg? How about 25-40 mmHg? Or a CPP of < 25 mmHg?
< 50 = EEG slowing
25-40 = EEG flat
< 25 = permanent brain damage
What is the average CMRO2?
3 - 3.8mL O2 / 100gm / min.
Coupling is the direct linear relationship of _____ to _____.
CMRO2 to CPP.
as CMRO2 increases, CPP will correspondingly increase
VAAs decrease ___1___ while increasing ___2___, disrupting the relationship between ___1____ to ____2____.
1 - CMRO2
2 - CPP
Glucose is the main energy substrate used by the brain. What is the average glucose consumption of the brain?
5mg / 100gm / min
For each 1 degree Celsius decrease in temperature, there is a corresponding ___-___% decrease in CMRO2.
7-8% decrease
(at 20 degrees Celsius, an EEG is flat showing no brain activity)
Do seizures increase or decrease CMRO2?
increase
Rehashing the concept of coupling…. as metabolic demands increase, will the cerebral blood flow increase or decrease?
increase
What is a normal value for ICP?
~10 mmHg
(temporary elevation of ICP occurs during coughing, Valsalva maneuvers, or hypertensive episodes)
Sustained elevated ICP > 15 mmHg decreases CPP and increases the risk of what?
cerebral ischemia
(severely increased ICP may lead to brainstem herniation through the foramen magnum)
How does hyperventilation decrease CBF?
by causing cerebral vascular vasoconstriction which decreases CBF
Decreasing CBV does what to ICP?
decreases it
Diuretics decrease brain tissue water content, doing what to ICP?
decreasing it
Ventriculostomy and intrathecal catheters allow CSF to drain, which does what to ICP?
decreases it
What occurs as a part of the Cushing reflex?
hypertension and bradycardia
If the Cushing reflex cannot adequately compensate for the worsening increases in ICP, then the Cushing’s triad appears. What is the triad?
hypertension, bradycardia, and irregular respirations
(these reflect severe increases in ICP and severe cerebral ischemia and impending herniation of the brain stem down through the foramen magnum)
What area of the brain do supratentorial tumors occupy?
midbrain and cerebral cortex
What area of the brain do infratentorial tumors occupy?
the vital centers of the cerebellum and brainstem
What is a risk of being in the sitting position?
venous air embolism
What is a risk of being in the lateral oblique position?
brachial plexus injury
What is a risk of being in the prone position?
postop vision loss (POVL)
What are the signs and symptoms of elevated ICP? (13)
headache
difficulty concentrating
memory disturbances
vision disturbances
vertigo
syncope
nausea
vomiting
severe headache
Cushing reflex and triad
seizures
coma
Volatile anesthetic agents _________ CMRO2 and _______ CBF.
decrease CMRO2
increase CBF
Do benzos, barbiturates, and propofol uncouple CMRO2 and CBF?
no, no they don’t
Do VAAs uncouple CMRO2 and CBF?
yes. they disrupt or “uncouple” this relationship by decreasing CMRO2 while increasing CBF.
(the direct relationship is changed to an inverse relationship)
Methods used to lower intracranial pressure address the need to decrease one or more of the three components of the cranial vault producing ICP- brain, blood, and CSF. What are three ways to decrease the brain component?
Diuretics- loop (furosemide 10 -100 mg) and osmotic (mannitol 12.5-50 gms)
Hypertonic saline (3%) at 20 cc/hr or 20cc bolus (23.2%)
Corticosteroids (dexamethasone 10-20 mg, solumedrol 1+ gms)
Methods used to lower intracranial pressure address the need to decrease one or more of the three components of the cranial vault producing ICP- brain, blood, and CSF. What are three ways to decrease the blood component?
Hyperventilation (pCO2 25-30 mm Hg)
Limit intravenous fluids (
Elevate head of bed (30 degrees)
Methods used to lower intracranial pressure address the need to decrease one or more of the three components of the cranial vault producing ICP- brain, blood, and CSF. What are three ways to decrease CSF component?
Ventriculostomy
Subdural drain
Lumbar drain (rarely) 
What do VAAs do to evoked potentials?
they increase latency and decrease amplitude
(a MAC of 0.5% is often acceptable)
Which IV fluids are acceptable for patients with elevated ICP?
NS and LR are superior to other fluids that contain higher percentages of free water
Why should you avoid dextrose containing IV solutions in someone with elevated ICP?
after the glucose is metabolized, free water is left over and the osmotic pressure is lowered.
dextrose solutions will also increase cerebral metabolism since the brain eats up metabolism.
What is the innervation and function of the glossopharyngeal nerve (IX)?
innervation - tongue, larynx
function - swallowing, larynx elevation
What is the innervation and function of the vagus nerve (X)?
innervation - most larynx and pharyngeal muscles, thoracic and abdominal organs
function - airway patency, parasympathetic effects, hemodynamics
What is the innervation and function of the accessory nerve (XI)?
innervation - neck and upper shoulders
function - some respiratory accessory muscle function, swallowing
What is the innervation and function of the hypoglossal nerve (XII)?
innervation - tongue
function - airway patency, swallowing
What is the most sensitive method of detecting a venous air emoblism?
transesophageal echocardiography
What is the least sensitive method of detecting a venous air embolism?
precordial stethoscope
With a VAE, air is present in the right atrium and the sound can be described as a __________ murmur.
millwheel
What do you do when you detect a VAE?
notify the surgeon.
if possible, lower the pt head.
turn off nitrous.
100% oxygen.
immediately aspirate blood and air with a 60cc syringe from the central line, if they have one.
support hemodynamics.
