10. Raised ICP

Question 1

what is a normal ICP and how is it measured?

Answer 1

volume of blood, brain and CSF enclosed within a rigid box
adults - 5-15 mmHg
children - 5-7mmHg
infants - 1.5-6 mmHg

Question 2

what is generally classed as a raised ICP?

Answer 2

above 20mmHg

Question 3

what is the monro-kellie doctrine?

Answer 3

Any increase in the volume of one of the intracranial
constituents (brain, blood or CSF) must be compensated
by a decrease in the volume of one of the others

Question 4

which components are pushed out first if there is an intracranial mass?

Answer 4

CSF and venous blood (as they are at the lowest pressure)

Question 5

how is the cerebral perfusion pressure calculated?

Answer 5

• CPP = mean arterial pressure (MAP) – ICP

Question 6

what is considered to be the normal CPP, MAP, ICP?

Answer 6

Normal CPP >70 mmHg
Normal MAP ~90mmHg
Normal ICP ~10 mmHg

Question 7

how does the body respond to increases in mean arterial pressure?

Answer 7

CPP increases, which then triggers cerebral autoregulation to maintain cerebral blood flow - vasoconstricts

Question 8

how does the body respond to increases if ICP?

Answer 8

CPP decreases so trigger cerebral autoregulation to maintain cerebrla blood flow - vasodilates

Question 9

is there a limit to the autoregulation of cerebral blood flow?

Answer 9

if CPP is less than 50 mmHg then cerebral blood flow can not be maintained as cerebral arterioles are maximally dilated

Question 10

how can ICP become dangerous?

Answer 10

usually maintained at a constant level up to a certain point beyond which ICP rises at an exponential rate

Question 11

what is the cushing’s triad/reflex?

Answer 11

A rise in ICP will initially lead to hypertension as the
body increases MAP to maintain CPP
• The increase in MAP is detected by baroreceptors which
stimulate a reflex bradycardia via increased vagal
activity (which can cause stomach ulcers as a dangerous
side effect)
• Continuing compression of the brainstem leads to
damage to respiratory centres causing irregular breathing

Question 12

what are some causes of raised ICP?

Answer 12

• due to too much blood within the cerebral vessels –raised MAP due to maliganent hypertension or raises venous pressure due to SVC obstruction
• due to too much blood outside of cerebral vessels, ie: haemorrhage
• too much CSF - hydrocephalus
  acquired - meningitis, trauma, ahemorrhage or tumours (compressing cerebral aqueducts)
  too much brain - cerebral oedema
  trauma, cerebral abscess, idiopathic intracranial hypertension

Question 13

what are some causes of hydrocephalus?

Answer 13

congenital - obstructive causes such as neural tube defects, aqueduct stenosis,
increased CSF production or decreased absorption

Question 14

what are the clinical signs of hydrocephalus?

Answer 14

bulging head with head circumference increasing faster than expected
sunsetting eyes due to direct compression of orbits and involement of CN3

Question 15

how is hydrocephalus managed?

Answer 15

tapping fontanelles with a needle
medium term drainage achieved by external ventricular drain
long term drainage by ventricular shunts

Question 16

what is idiopathic intracranial hypertension/benign intracranial hypertension?

Answer 16

headache and visual disturbance
obese middle aged females
raised opening pressure on lumbar puncture
treated with weight loss and BP control

Question 17

why can lumbar puncture be dangerous?

Answer 17

if pathology can precipitate brain herniation

Question 18

what are some of the clinical presentations of raised ICP?

Answer 18

Headache
o Constant
o Worse in the morning
o Worse on bending / straining
• Nausea and vomiting
• Difficulty concentrating or drowsiness
o Effect on daily life
• Confusion
• Double vision
o Problems with accommodation (early sign,
pupillary dilatation a late sign)
o Maybe effects on acuity
o Visual field defects
o Papilloedema (swelling of optic disc)
• Focal neurological signs
o Depends on where lesion is
• Seizures

Question 19

what are the types of herniation that can occur due to raised ICP?

Answer 19

• tonsillar herniation - herniate through foramen magnus, compressing medulla
• subfalcine hernation - cingulate gyrus pushed under free edge of falx cerebri so can compress ACA as it loops over corpus callosum
• uncal hernation - uncus of temporal love herniate through tentorial notch, compressing midbrain causing 3rd nerve palsy amd can compress cerebral peduncle - contralateral hemiparesis
• centre downward hernation - medial temporal lobe and other midline structure through tentorial notch
• external herniation through skull fracture

Question 20

how are raised ICP’s managed?

Answer 20

• airway and breathing to maintain O2 and remove CO2
• maintain MAP and CPP
• Sedation, analgesia and paralysis - Decrease metabolic demand and Prevents cough / shivering that might increase ICP
  further
• Head up tilt which Improves cerebral venous drainage
• Prevent hyperthermia and Therapeutic hypothermia may be beneficial
• Prevent seizures, reduce metabolic demand
• Nutrition and proton pump inhibitors so Improved healing of injuries and prevent stomach
  ulcers due to increased vagal activity

Question 21

what are the treatments available for raised ICP?

Answer 21

maannitol or hypertonic saline - osmotic diuresis
ventricular drainage
decompressive craniectomy as last resort