ICP and cerebral oedema

Question 1

cerebral perfusion pressure

Answer 1

perfusion of brain dependent on pressure difference between arteries and veins (CPP)

mean cerebral venous pressure difficult to measure and approximates to ICP

CPP = MAP - ICP

usually ~80mmHg

Question 2

monro-kellie hypothesis

Answer 2

skull is rigid box
sum of intracranial volumes of blood, brain, CSF and other components (e.g. tumour) is constant

increase in volume of one components must be offset by decrease in others, or associated with rise in ICP

once compensatory mechanisms exhausts (blood and CSF) ICP rises.

Question 3

regulation of cerebral artery blood vessels

Answer 3

cerebral metabolism
carbon dioxide and oxygen
autoregulation
neurohumoral factors
blood viscosity
temp
drugs

radius of cerebral arteries important –> effect on CBF & increased radius increases blood volume which increases ICP and reduces CPP

Question 4

Mx elevated ICP

Answer 4

generally physiological homeostasis
CSF drainage
head of bed elevation to 30°
sedation
diuretics
hyperventilation
hypothermia
depressive craniotomy