Brain 2 Flashcards
The ______ cushions the brain, provides buoyancy, and delivers optimal conditions for neurologic function.
cerebrospinal fluid
CSF is located in the
ventricles, cisterns, and subarachnoid space in the brain and spinal cord
The total CSF volume is
~150 mL
CSF is produced by the
choroid plexus (~30 mL/hr)
CSF is absorbed in the
arachnoid villi in the superior sagittal sinus
The blood brain barrier separates the
CSF from the plasma
The blood brain barrier becomes dysfunctional at sites of
tumor, injury, infection, or ischemia
The blood-brain barrier isn’t present at the _______, which explains how some drugs that can’t pass through the BBB can elicit N & V.
chemoreceptor trigger zone
The blood brain barrier is poorly developed in the
neonate
The specific gravity of CSF is
1.002-1.009
CSF pressure is
5-15 mmHg
Reabsorption of CSF is dependent on the pressure gradient between
the CSF and venous circulation
What is the mnemonic for CSF flow in the brain?
Love My 3 Silly 4 Lorn Magpies
Describe the mnemonic for CSF flow in the brain
Lateral ventricles
Monro (foramen)
3rd ventricle
Sylvius (aqueduct)
4th ventricle
Luschka
Magendie
_______ is the excessive accumulation of CSF in the brain.
Hydrocephalus
What are the two types of hydrocephalus?
obstructive
communicating
Describe obstructive hydrocephalus.
Obstruction to CSF flow in the ventricular system (most common)
Describe communicating hydrocephalus.
a. decreased CSF absorption by the arachnoid villi (e.g. intracranial hemorrhage)
b. Overproduction of CSF (very rare)
Surgical management for either type of hydrocephalus depends on the cause and can include
placing a catheter in the cerebral ventricles to drain CSF
placing a ventriculoatrial shunt (brain to heart)
or ventriculoperitoneal shunt (brain to belly)
Where in the brain is the blood-brain barrier NOT present?
chemoreceptor trigger zone
hypothalamus
pineal gland
posterior pituitary gland
choroid plexus
The 5 determinants of cerebral blood flow include:
cerebral metabolic rate for oxygen (CMRO2)
cerebral perfusion pressure
PaCO2
PaO2
Venous pressure
The brain __________ to protect against blood pressure fluctuations that accompany everyday life.
autoregulates its blood flow
Describe the relationship between cerebral blood flow and CMRO2
they are coupled
the greater the need for oxygen, the more blood flow there will be to satisfy this need
CMRO2 is decreased by
hypothermia, halogenated anesthetics, propofol, etomidate, and barbiturates
CMRO2 is increased by
hyperthermia, seizures, ketamine, and nitrous oxide
Cerebral blood flow autoregulates between a cerebral perfusion pressure of
50-150 mmHg
in reality, not all patients have such a wide range of autoregulation
There’s a risk of ________ when CPP is below the lower limit of autoregulation.
hypoperfusion
There’s a risk of _______ and ________ when CPP is above the upper limit of autoregulation.
cerebral edema & hemorrhage
A PaO2 below 50-60 mmHg causes
cerebral vasodilation and increases CBF
A high venous pressure reduces _______ and increases ________
cerebral venous drainage; and increases cerebral volume
What is the relationship between PaCO2 and CBF?
there is a linear relationship
will both go up or down together
For every _______ increase in PaCO2, CBF will increase by
1 mmHg; 1-2 mL/100 g brain tissue/min.
Maximal cerebral vasoconstriction occurs at a PaCO2 of
25 mmHg
Maximal cerebral vasodilation occurs at a PaCO2 of
80-100 mmHg
Cerebral blood flow is equal to
Cerebral perfusion pressure/cerebral vascular resistance
At a cerebral blood flow of 20 mL/100 g tissue/min we see evidence of
ischemia
At a CBF <15 mL/100 g tissue/min, we see
membrane failure and cell death
Cerebral perfusion pressure is equal to
MAP-ICP
Things that abolish or reduce the effectiveness of autoregulation include
intracranial tumor
head trauma
volatile anesthetics
When PaO2 is above 60 mmHg, cerebral blood flow is
unaffected by PaO2
Conditions that impair venous drainage include
jugular compression due to improper head positioning
increased intrathoracic pressure secondary to coughing or PEEP
vena cava thrombosis
vena cava syndrome
A fixed and dilated pupil suggests herniation of the:
a. cingulate gyrus
b. choroid plexus
c. temporal uncus
d. cerebellar tonsils
C. temporal uncus
The most common site of transtentorial herniation is at the
temporal uncus
Normal ICP is
5-15 mmHg
Intracranial hypertension occurs when ICP exceeds
20 mmHg
Signs and symptoms of intracranial hypertension includes
headache, N/V, papilledema, focal neurologic deficit, decreased LOC, seizures, and coma
Cushing’s triad is composed of
hypertension
bradycardia
irregular respirations
it is a sign of intracranial HTN
Describe the Monro-Kellie hypothesis.
the brain, blood, and CSF exist in the confines of the cranium. an increase in one of these components must be countered with a decrease in one or both of the others or an increase in the pressure inside the cranium will occur
Herniation at the temporal uncus applies pressure to the
oculomotor nerve (CN 3), making it ischemia; this manifests as a fixed and dilated pupil
The gold standard of ICP measurement is
intraventricular catheter
ICP measurement is indicated with a GCS score of
<7
