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The Nervous System: Pathology > Clinical aspects of cerebral perfusion and ICP > Flashcards

Clinical aspects of cerebral perfusion and ICP Flashcards

1
Q

What is the normal average blood flow though the overall brain tissue

A

55 to 60ml/100g brain tissue per minute

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2
Q

What is the normal average blood flow though the grey matter

A

75ml/100g/minute

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3
Q

What is the normal average blood flow though the white matter

A

45ml/100g/minute

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4
Q

What is the blood flow in ischaemia through the brain

A

20ml/100g/minute

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5
Q

What is the blood flow rate where permanent damage can occur

A

drops below 10ml/100g/minute

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6
Q

What is the most significant factor in determining cerebral blood flow

A

Cerebral perfusion pressure - the effective blood pressure gradient across the brain

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7
Q

What is the equation for cerebral perfusion pressure

A

CPP = MAP - ICP

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8
Q

What affect does increasing the ICP have on the CPP

A

Increased ICP causes the CPP to decrease

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9
Q

What is the equation for MAP: Mean arterial pressure

A

MAP = DP +1/3PP
or
MAP = 2/3DP + 1/3SP

(PP = SP-DP)

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10
Q

What is three factors that regulate cerebral blood flow under physiological conditions

A

Cerebral prefusiion pressure

Concentration of arterial CO2

Arterial PO2

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11
Q

Define cerebral auto-regulation

A

The ability to maintain constant blood flow to the brain over a wide range of CPP (50-150 mm Hg)

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12
Q

What is the cerebral auto-regulation when the CPP is low

A

cerebral arterioles dilate to allow adequate flow at the decreased pressure

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13
Q

What is the cerebral auto-regulation when the CPP is high

A

cerebral arterioles constrict

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14
Q

How does the concentration of arterial CO2 and PaO2 regulate cerebral blood flow

A

Decreased levels causes arteriolar constrictions therefore lowering cerebral blood flow

eg hyperventilation

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15
Q

What are the Pathological conditions where cerebral blood flow can not be regulated

A

CPP exceeds 150mmHg - hypertensive crisis

Exudate of fluid from vascular system with resultant vasogenic edema

Toxins: CO2 - diffuses cerebrovascular dilation and inhibit proper auto-regulation

During the first 4 to 5 days of head trauma, many patients can experience a disruption in cerebral autoregulation

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16
Q

What is cerebral edema

A

state of increased brain volume as a result of increase on water content

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17
Q

What is the three types of edema in the brain

A

Vasogenic

Cytotoxic

Interstitial

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18
Q

What is the pathogenesis and location of vasogenic edema (extracellular)

A

Increased capillary permeability located mainly in white matter

Composed of plasma filtrate (plasma proteins)

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19
Q

What is the pathogenesis and location of cytotoxic edema (intracellular`)

A

Cellular swelling in the grey and white matter

Composed of increased intracellular water and sodium (due to failure of membrane transport)

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20
Q

What is the pathogenesis interstitial deem

A

Increased brain water due to impairment in absorption of CSF, composed of the CSF

and Located in the periventricular white matter in hydrocephalus

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21
Q

What types of edema have an increase in extracellular fluid

A

Vasogenic

Interstitial

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22
Q

What type of edema is effective to steroids

A

Vasogenic

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23
Q

What type of deem is effective to mannitol

A

Vasogenic
Cytotoxic
(Interstitial ??)

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24
Q

What is the potential pathological lesion resulting in vasogenic edema

A

Primary or metastatic tumour

Abscess

Late stages of infarction

Trauma

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25
What is the potential pathological lesion resulting in cytotoxic edema
Early stages of infarction water intoxication
26
What is the potential pathological lesion resulting in interstitial edema
Obstructive or communicating hydrocephalus
27
What is the composition and purpose of the blood brain barrier
Composed of astrocytic foot process wrapping around a capillary endothelium composed of tight junctions Endothelial tight junctions are the barrier to the passive movement of many substances in order to protect the sensitive neural tissue from toxic materials
28
How are lipid soluble substance transported across the blood brain barrier
usually penetrate all capillary endothelial cell membranes in a passive manner
29
How are amino acids and sugars transported across the blood brain barrier
transported across the capillary endothelium by specific carrier-mediated mechanisms
30
What is the three components of the cranium
Brain Blood CSF
31
How does the intra- cranium respond to changes in pressure and volume
Compliance - change in volume observed for a given change in pressure Elastance - change in pressure observed for a given change in volume
32
How is compliance shown when a new intracrhail mass is introduced increasing the pressure in the brain
a compensatory change in volume must occur through a reciprocal decrease in venous blood or CSF to keep the total intracranial volume constant
33
How is elastane of the intra-cranium represented
accommodation to outward expansion of an intracranial mass
34
What is the homeostatic mechanism of the venous system in compliance to decrease volume in the cranium
The venous system collapses easily and squeezes venous blood out through the jugular veins or through the emissary and scalp veins
35
What is the homeostatic mechanism of CSF in compliance to decrease volume in the cranium
CSF can be displaced from the ventricular system through the foramina of Luschka and Magendie into the spinal subarachnoid space
36
How long does the "pressure buffering" mechanism of venous blood and CSF compliance last
Until critical volume is reached
37
What natural happens at when homeostatic mechanisms causes "critical volume"
Intracranial hypertension as small volumetric changes result in significant increase in pressure
38
What are the three waves, on an ICP waveform
P1= Percussion wave P2 = Tidal wave P3 = Dicrotic wave
39
What does P1: Percussion wave represent
``` Arterial pulsation (systolic pressure, large intracranial arteries, and choroid plexus) ```
40
What does P2: tidal wave represent
Intra cranial compliance
41
What does P3: dicrotic wave represent
Venous pulsation
42
What affect does an increased/decreased systolic BP have on P1
Increased: Big P1 Decreased: P1 decreases and eventually disappears
43
What does a prominent P2 wave indicate
Mass lesion is increasing volume Intracranial compliance is decreased Inspiratory breath is being held
44
If P2 and P3 waves is not present what does this indicate
Hyperventilation
45
How is intracranial hypertension indicated in in ICP waveforms
When P2 is higher than P1
46
How do you define Lindbergh A waves
Abrupt elevation in ICP for 5 to 20 minutes followed by a rapid fall in the pressure to resting levels The amplitude may reach as high as 50 to 100 mm Hg
47
How do you define Lindbergh B waves
Frequency of 0.5 to 2 waves per minute, are related to rhythmic variations in breathing
48
How do you define Lindbergh C waves
Rhythmic variations related to waves of systemic blood pressure and have smaller amplitude
49
What is the cause of A waves
ICP Exceeds the limits of cerebral compliance
50
What is the cause of B waves
Respiratory changes Variation in cerebral blood flow
51
How do you mange increased ICP
Head end elevation: facilitate venous return Mannitol/ Hypertonic saline Hyperventilation: decrease CBF (temporary measure) Barbiturate coma: decrease cerebral metabolism, CBF Surgical decompression
52
What occurs in stage 1 cushings relfex
ICP increases more than MAP This compresses the cerebral arterioles and decreases cerebral blood flow, and the ischaemic conditions activates the autonomic nervous system
53
How does a sympathetic response occur in cushings reflex
Sympathetic response via alpha 1-adrenergic receptors, causing constriction of body's arteries and increases the rate of heart contractions and cardiac output causing tachycardia
54
What is the affect of cushing contraction of bodies arteries
raises the total resistance of blood flow, elevating blood pressure to high levels, which is known as hypertension.
55
How is a parasympathetic response triggered in cushions reflex
baroreceptors in the aortic arch detect the increase in blood pressure and trigger a parasympathetic response via the Vagus nerve.
56
What occurs due to parasympathetic stimulation in cushions reflex
This induces bradycardia signifying the second stage of the reflex
57
How does bradycardia also occur in cushing reflex
Due to mechanical distortion of medulla
58
What is the cushions triad of symptoms
Increased blood pressure irregular breathing Bradycardia
59
What occurs in brain tissue oxygenation monitoring
Probe to monitor oxygenation of tissue Detect and treat low oxygenation, increasing Cerebral perfusion pressure
60
What occurs in micro dialysis
Investigate brain metabolism By implantation of specially designed catheters collecting small-molecular-weight substances to help measure and identify neurotransmitters, peptides, and other substances

The Nervous System: Pathology (25 decks)

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