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Year 2 - Nervous > Clinical aspects of cerebral perfusion & ICP > Flashcards

Clinical aspects of cerebral perfusion & ICP Flashcards

1
Q

Cerebral blood flow is what percentage of cardiac output

A

15%

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2
Q

Brain ischaemia occurs at what perfusion rate

A

20ml/100g tissue/min

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3
Q

What pressure determines cerebral blood flow at any given time

A

Cerebral perfusion pressure

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4
Q

Cerebral perfusion pressure (CPP) =

A

MAP - ICP (intracranial pressure)

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5
Q

MAP =

A

Diastolic pressure + 1/3 pulse pressure

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6
Q

Increased ICP causes cerebral perfusion pressure to increase or decrease

A

Decrease

Remember CPP = MAP - ICP

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7
Q

Factors that regulate cerebral blood flow (3)

A

CPP
Conc. of arterial PCO2
Conc. of arterial PO2

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8
Q

Weight of brain

A

1300-1400g

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9
Q

Name 3 types of oedema

A

Vasogenic (extracellular)
Cytotoxic (intracellular)
Interstitial

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10
Q

Vasogenic oedema

  • what is it due to
  • location of oedema
  • composition of oedema
  • extracellular fluid levels increased or decreased
  • effect of steroids
  • effect of mannitol
A 
Increased capillary permeability
Mainly white matter
Plasma filtrate
Increased
Effective
Effective
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11
Q

Cytotoxic oedema

  • what is it due to
  • location of oedema
  • composition of oedema
  • extracellular fluid levels increased or decreased
  • effect of steroids
  • effect of mannitol
A

Cellular swelling (of neurons and glial cells) due to failure of Na/K pump

Grey and white matter

Increased intracellular water and sodium

Decreased

No effect of steroids

Mannitol effective

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12
Q

Interstitial oedema

  • what is it due to
  • location of oedema
  • composition of oedema
  • extracellular levels increased or decreased
  • effect of steroids
  • effect of mannitol
A

increased brain water due to impairment of absorption of CSF

periventricular white matter

CSF based

Extracellular fluid increased

No effect of steroids

Mannitol sometimes has an effect, sometimes doesn’t

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13
Q

Causes of vasogenic oedema (4)

A

Tumour
Abscess
Late stage infarction
Trauma

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14
Q

Causes of cytotoxic oedema (2)

A

Early stages of infarction

Water intoxication

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15
Q

Cause of interstitial oedema

A

Hydrocephalus (communicating or non-communicating)

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16
Q

What condition do you get interstitial oedema

A

Hydrocephalus

17
Q

Percentage of brain substance, blood and CSF within the cranium

A

80%
10%
10%

18
Q

What is the munro-kelly doctrine

A

Pressure-volume relationship that aims to keep a dynamic equilibrium among the essential non-compressible components inside the rigid compartment of the skull

Essentially meaning that the sum of the volumes of brain substance , CSF, and intracranial blood is constant (i.e. total intracranial volume is always constant)

19
Q

When a new intracranial mass is introduced, what happens in respect to the munro-kelly doctrine

A

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

20
Q

Define compliance

A

change in volume observed for a given change in pressure

21
Q

Define elastance + what does the term mean in association with intracranial masses

A

change in pressure observed for a given change in volume (INVERSE OF COMPLIANCE)

Refers to the accommodation to outward expansion of an intracranial mass

22
Q

Homeostatic compensatory mechanisms in response to intracranial masses (2)

A

1) Venous system can collapse to squeeze blood out jugular veins or emissary and scalp veins
2) CSF can be displaced into subarachnoid space

23
Q

What happens when homeostatic compensatory mechanisms in response to intracranial masses have been exhausted

A

The innate homeostatic pressure-buffering mechanisms keep compliance flat until a “critical volume” is reached

After this critical volume, small changes in volume produce significant increase in pressures, and intracranial hypertension naturally follows

24
Q

As compliance decreases, does ICP increase or decrease

A

Increase

25
Q

What is the cushing’s reflex

A

AKA vasopressor (anti-hypotensive) response

physiological response to raised ICP (causing decreased CPP), resulting in CUSHING’S TRIAD

26
Q

What does the Cushing’s triad consist of

A

Hypertension
Irregular breathing
Bradycardia

27
Q

Cushing’s reflex comes about due to raised ICP (causing decreased CPP), the decreased CPP activates what system (1) which brings about what response (2) to cause the cushing’s triad

A

AUTONOMIC NERVOUS SYSTEM

Sympathetic response – a1 adrenergic receptors stimulated to cause HYPERTENSION & TACHYCARDIA

Aortic baroreceptors stimulate vagus nerve –> BRADYCARDIA

28
Q

Management of raised ICP (6)

A

Head elevation - to improve venous return to heart

Mannitol/hypertonic saline - short acting

Hyperventilation - to decrease CPP, short acting

Barbiturate coma - to decrease cerebral metabolism & CPP

Surgical decompression

Brain tissue oxygenation monitoring with probe

29
Q

Normal ICP range

A

7-15 mmHg

30
Q

3 types of ICP pulse waveforms (Correlate to arterial pressure)

A

P1 wave = percussion wave
P2 wave = tidal wave
P3 wave = dicrotic wave

31
Q

What are Lundberg A waves

A

Steep increases in ICP lasting for 5 to 10 minutes.

They are always pathological and represent reduced intracranial hypertension indicative of early brain herniation

32
Q

What are Lundberg B waves

A

oscillations of ICP at a frequency of 0.5 to 2 waves/min and are associated with an unstable ICP

33
Q

What are Lundberg C waves

A

oscillations with a frequency of 4-8 waves/min. They have been documented in healthy subjects and are probably caused by interaction between the cardiac and respiratory cycles.

Related to waves of systemic BP

34
Q

What is cerebral autoregulation

A

ability to maintain constant blood flow to the brain over a WIDE RANGE OF CPP (50-150mmHg)

35
Q

If CPP low, what do cerebral arterioles do

A

dilate to compensate for the decreased pressure and vice versa if CPP is high

36
Q

In some pathologies, cerebral blood flow can’t be autoregulated (ability to maintain constant blood flow to the brain over CPP range of 50-150mmHg) - describe some of these pathologies (3)

A

if CPP exceeds 150mmHg, such has in HYPERTENSIVE CRISIS, the autoregulatory system fails as it’s not within the range

Toxins like CO2 can cause diffuse cerebrovascular dilation and inhibit proper autoregulation

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

Year 2 - Nervous (39 decks)

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