Cerebral Perfusion and Intracranial Pressure

Question 1

When does permanent cerebral damage usually occur, with reference to blood flow?

Answer 1

When cerebral blood flow drops to below 10ml/100g/minute

Question 2

What factors determine cerebral blood flow?

Answer 2

Cerebral perfusion pressure (most significant)
Concentration of arterial CO2
Arterial PO2

Question 3

What is the relationship between cerebral perfusion pressure, mean arterial pressure and intracranial pressure?

Answer 3

CPP = MAP - ICP

Question 4

What is the role of cerebral autoregulation?

Answer 4

To maintain a constant blood flow to the brain over a wide range of CPP

Question 5

How does cerebral autoregulation maintain constant blood flow to the brain?

Answer 5

CPP is low, cerebral arterioles dilate to allow adequate flow at the decreased pressure
CPP is high, cerebral arterioles constrict

Question 6

What are the causes of failure of cerebral autoregulation?

Answer 6

Hypertensive crisis
Exudation of fluid from vascular system
Certain toxins
First 5 days of head trauma
Cerebral oedema

Question 7

What is the blood brain barrier made of?

Answer 7

Astrocytic foot processes wrapping around a capillary endothelium composed of tight junctions
Endothelial tight junctions are barrier to passive movement of many substances

Question 8

What mechanisms allow for materials to be transported across the endothelial cells of the blood brain barrier?

Answer 8

Lipid-soluble substances can usually penetrate all capillary endothelial cell membranes in passive manner
Amino acids and sugars are transported across capillary endothelium by specific carrier-mediated mechanisms

Question 9

What compensatory mechanisms are there to allow for slight increases in volume or pressure in the cranium?

Answer 9

Decrease in volume- venous system collapses easily and squeezes venous blood out through jugular veins
CSF can be displaced from ventricular system into spinal subarachnoid space

Question 10

What is Cushing’s reflex?

Answer 10

A vasopressor response resulting in hypertension, irregular breathing and bradycardia

Question 11

How is an increased intracranial pressure managed?

Answer 11

Head end elevation to facilitate venous return
Hypertonic saline
Surgical decompression
Treat hyperventilation