Clinical aspects of cerebral perfusion and ICP

Question 1

What percentage of cardiac output does the brain receive?

Answer 1

15%

Question 2

At what rate of flow does cerebral ischaemia occur?

Answer 2

20ml/100g/minute

Question 3

At what blood flow rate does permanent damage usually occur?

Answer 3

10ml/100g/minute

Question 4

What is the most significant factor that determines cerebral blood flow at any given time?

Answer 4

Cerebral perfusion pressure (CPP)?

Question 5

How is the CPP calculated?

Answer 5

CPP=MAP-ICP

Question 6

What effect does raised ICP have on CPP?

Answer 6

Decreases it

Question 7

What factors regulate cerebral blood flow under normal physiological conditions?

Answer 7

CPP
Concentration of arterial CO2
Arterial PO2

Question 8

What response do cerebral arterioles have to raised CPP?

Answer 8

Constrict

Question 9

What states may result in failure of cerebral autoregulation?

Answer 9

CPP exceeds 150mmHG
Toxins such as CO2 may cause diffuse cerebrovascular dilation
Head trauma
Cerebral oedema

Question 10

What provides the barrier at the BBB?

Answer 10

Endothelial tight junction

Question 11

How are amino acids and sugars transported across the BBB?

Answer 11

Specific carrier-mediated mechanisms

Question 12

What is the Monro-Kelly doctrine?

Answer 12

When a new intracranial mass is introduced, a compensatory change in volume must occur through a reciprocal decrease in venous blood or CSF to keep the total intracranial volume constant

Question 13

What is compliance?

Answer 13

Change in volume for a given change in pressure

Question 14

What is elastance?

Answer 14

Change in pressure for a given change in volume

Question 15

What do Lundberg A waves represent?

Answer 15

Abrupt elevation of ICP for 5 to 20 minutes followed bya rapid fall in the pressure to resting level

Question 16

What do lundberg B waves represent?

Answer 16

Rhythmic variation of breathing

Question 17

What do Lundberg C waves represent?

Answer 17

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

Question 18

What is Cushing’s reflex?

Answer 18

The vasopressor response

Raised systolic BP
Decreased HR
Decreased RR

Question 19

What are some forms of management for raised ICP?

Answer 19

Head end elevation to facilitate venous return
Mannitol (diuretic)
Hyperventilation to decrease CBF
Surgical decompression

Question 20

What is brain tissue oxygenation monitoring?

Answer 20

Probe to monitor oxygenation of tissue

Detect and treat low oxygenation, increasing CPP

Question 21

What is Micro-dialysis?

Answer 21

Investigates brain metabolism
Implantation of specially designed catheters
Collects small molecular weight substances to help measure and identify neurotransmitters, peptides and others