Clinical Aspects of Cerebral Perfusion and ICP Flashcards Preview

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Flashcards in Clinical Aspects of Cerebral Perfusion and ICP Deck (19)
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1
Q

How much blood flow do white and grey matter receive per minute? What level of blood flow do ischaemia and permanent damage usually occur at?

A
  • Grey matter: 75mL/100g/minute
  • White matter: 45Ml/100g/minute
  • Ischaemia: 20mL/100g/minute
  • Permanent damage: 10mL/100g/minute
    (brain = 15% of CO)
2
Q

What are the most significant factors determining cerebral perfusion pressure? What is it determined by?

A
  • CPP: cerebral perfusion pressure

- CPP = MAP - ICP

3
Q

What causes cerebral perfusion pressure to decrease?

A

Increased intracranial pressure (ICP)

4
Q

Factors that regulate cerebral blood flow under physiological conditions?

A
  • CPP
  • Concentration of arterial CO2
  • Arterial PO2
5
Q

What is cerebral autoregulation?

A
  • The ability to maintain adequate blood flow to the brain across a large range of CPP (50-150 mmHg). Done via constriction / dilation of arterioles
  • CPP = MAP - ICP
6
Q

What is vasogenic oedema?

A

Oedema in the cerebrum due to disruption of the blood brain barrier (can be caused by too high of CPP)

7
Q

What is cerebral oedema often a cause of?

A

Intracranial hypertension

ICP is higher so MAP has to increase to maintain CPP?

8
Q

What forms the basis of the blood brain barrier? (BBB)

A
  • Tight junctions between the endothelium of cerebral arterioles
  • Astrocytic foot processes surround brain capillaries and induce the formation of these tight junctions during development
9
Q

What materials are usually naturally transported across the endothelial cells of the BBB?

A
  • Lipid soluble substances (passive)

- Amino acids and sugars via carrier mediated transport

10
Q

What is the Monro-Kelly Doctrine? (cerebral volume)

A

when a new intracranial mass is introduced, there must be an accompanying decrease in CSF or venous blood volume to keep ICP constant

11
Q

What is compliance?

A
  • Change in volume for a given change in pressure

- dV / dP

12
Q

What is elastance?

A
  • Change in pressure observed for a given change in volume
  • dP / dV

Represents the accommodation to outward expansion of an intracranial mass

13
Q

What are the mechanisms for maintaining homeostasis of ICP? Over what sort of pressure range are they effective?

A
  • Venous collapse: squeezes blood out via jugular & emissary / scalp veins
  • CSF displacement: out through foramina of Luschka and Magendie into spinal subarachnoid space
  • Mechanisms work over pressure changes of about 8-15mmHg
14
Q

Once the innate homeostatic mechanisms regulating ICP are exhausted what happens?

A
  • Once a “critical volume” is reached, additional small changes in volume produce significant changes in pressure
  • ICP rises and intracranial hypertension ensues
15
Q

What is an extraventricular drain (EVD) used for?

A
  • Treatment of hydrocephalus and elevated ICP

- Monitoring intracranial pressure

16
Q

What is Cushing’s Reflex?

A
  • AKA Vasopressor response
  • It is the nervous response to raised ICP, consisting of hypertension, irregular breathing and bradycardia
  • Often seen at the terminal stages of brain trauma, may indicate brain herniation
17
Q

Explain the mechanism of the Cushing Reflex

A
  • ICP > MAP, cerebral arteries compressed = ischaemia
  • Sympathetic response: alpha-1 adrenergic compresses arterioles and induces tachycardia
  • Baroreceptors detect increased MAP & induce bradycardia via vagus nerve
  • Herniation / distortion of the medulla can result in irregular breathing
18
Q

Function of the Cushing Reflex?

A

It is a last ditch effort to maintain adequate CPP in the brain

19
Q

What are some different ways to manage increased ICP?

A
  • Barbituate coma: decreases cerebral metabolism

- Surgical decompression (EVD)

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