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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
Q

What is the potential pathological lesion resulting in cytotoxic edema

A

Early stages of infarction

water intoxication

26
Q

What is the potential pathological lesion resulting in interstitial edema

A

Obstructive or communicating hydrocephalus

27
Q

What is the composition and purpose of the blood brain barrier

A

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
Q

How are lipid soluble substance transported across the blood brain barrier

A

usually penetrate all capillary endothelial cell membranes in a passive manner

29
Q

How are amino acids and sugars transported across the blood brain barrier

A

transported across the capillary endothelium by specific carrier-mediated mechanisms

30
Q

What is the three components of the cranium

A

Brain
Blood
CSF

31
Q

How does the intra- cranium respond to changes in pressure and volume

A

Compliance - change in volume observed for a given change in pressure

Elastance - change in pressure observed for a given change in volume

32
Q

How is compliance shown when a new intracrhail mass is introduced increasing the pressure in the brain

A

a compensatory change in volume must occur through a reciprocal decrease in venous blood or CSF to keep the total intracranial volume constant

33
Q

How is elastane of the intra-cranium represented

A

accommodation to outward expansion of an intracranial mass

34
Q

What is the homeostatic mechanism of the venous system in compliance to decrease volume in the cranium

A

The venous system collapses easily and squeezes venous blood out through the jugular veins or through the emissary and scalp veins

35
Q

What is the homeostatic mechanism of CSF in compliance to decrease volume in the cranium

A

CSF can be displaced from the ventricular system through the foramina of Luschka and Magendie into the spinal subarachnoid space

36
Q

How long does the “pressure buffering” mechanism of venous blood and CSF compliance last

A

Until critical volume is reached

37
Q

What natural happens at when homeostatic mechanisms causes “critical volume”

A

Intracranial hypertension as small volumetric changes result in significant increase in pressure

38
Q

What are the three waves, on an ICP waveform

A

P1= Percussion wave

P2 = Tidal wave

P3 = Dicrotic wave

39
Q

What does P1: Percussion wave represent

A 
Arterial pulsation 
(systolic pressure, large intracranial arteries, and choroid plexus)
40
Q

What does P2: tidal wave represent

A

Intra cranial compliance

41
Q

What does P3: dicrotic wave represent

A

Venous pulsation

42
Q

What affect does an increased/decreased systolic BP have on P1

A

Increased: Big P1

Decreased: P1 decreases and eventually disappears

43
Q

What does a prominent P2 wave indicate

A

Mass lesion is increasing volume

Intracranial compliance is decreased

Inspiratory breath is being held

44
Q

If P2 and P3 waves is not present what does this indicate

A

Hyperventilation

45
Q

How is intracranial hypertension indicated in in ICP waveforms

A

When P2 is higher than P1

46
Q

How do you define Lindbergh A waves

A

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
Q

How do you define Lindbergh B waves

A

Frequency of 0.5 to 2 waves per minute, are related to rhythmic variations in breathing

48
Q

How do you define Lindbergh C waves

A

Rhythmic variations related to waves of systemic blood pressure and have smaller amplitude

49
Q

What is the cause of A waves

A

ICP Exceeds the limits of cerebral compliance

50
Q

What is the cause of B waves

A

Respiratory changes

Variation in cerebral blood flow

51
Q

How do you mange increased ICP

A

Head end elevation: facilitate venous return

Mannitol/ Hypertonic saline

Hyperventilation: decrease CBF (temporary measure)

Barbiturate coma: decrease cerebral metabolism, CBF

Surgical decompression

52
Q

What occurs in stage 1 cushings relfex

A

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
Q

How does a sympathetic response occur in cushings reflex

A

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
Q

What is the affect of cushing contraction of bodies arteries

A

raises the total resistance of blood flow, elevating blood pressure to high levels, which is known as hypertension.

55
Q

How is a parasympathetic response triggered in cushions reflex

A

baroreceptors in the aortic arch detect the increase in blood pressure and trigger a parasympathetic response via the Vagus nerve.

56
Q

What occurs due to parasympathetic stimulation in cushions reflex

A

This induces bradycardia signifying the second stage of the reflex

57
Q

How does bradycardia also occur in cushing reflex

A

Due to mechanical distortion of medulla

58
Q

What is the cushions triad of symptoms

A

Increased blood pressure

irregular breathing

Bradycardia

59
Q

What occurs in brain tissue oxygenation monitoring

A

Probe to monitor oxygenation of tissue

Detect and treat low oxygenation, increasing Cerebral perfusion pressure

60
Q

What occurs in micro dialysis

A

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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