Intracranial Pressure Flashcards
What is the best eye response in the GCS?
Open spontaneously (4)
Open to verbal command (3)
Open to pain (2)
Does not open eyes (1)
What is the best verbal response in the GCS?
Oriented (5) Confused speech (4) Inappropriate words (3) Incomprehensible sounds (2) No speech (1)
What is the best motor response in the GCS?
Obeys commands (6) Localised to pain (5) Normal flexion to pain (4) Abnormal flexion to pain (3) Extension to pain (2) No movement (1)
What classifies a coma?
GCS score of 8 or less
Describe the physiological processes in raised ICP
Haemorrhage (“mass effect”)
Disruption of blood brain barrier -> Increased ECF
(Vasogenic Oedema)
Membrane Failure -> influx of Ca -> cellular swelling (cytotoxic oedema)
Influx of inflammatory mediators
What are the secondary effects of raised intracranial pressure
Anatomical
-Herniation syndromes
Cellular
-Decreased cerebral perfusion
What is the Monro-Kellie Doctrine?
Brain exists in a fixed intracranial space which is a constant.
This constant is filled with CSF, Blood, Brain, and other
If other increases the something else has to decrease to keep same volume
How is a haematoma compensated for initially preventing a large increase in ICP?
Interstitial fluid is squeezed out
CSF shunted into thecal sac
Blood shunted out of head via internal jugular vein
What causes the lucid interval in jead trauma?
Compensatory measures by shunting CSF, Blood and squeezing interstitial fluid out.
This doesnt last for ever and you get rapid increase in ICP and drop in consciousness
How is cerebral perfusion pressure calculated?
MAP - ICP = CPP
MAP battles against ICP to keep CPP.
If ICP increases CPP will decrease
How is MAP calculated?
Diastolic BP + 1/3 pulse pressure
What is the normal CPP?
80 mmHg
What is the normal MAP?
90mmHg
What is the normal ICP?
5-15mmHg
How much cardiac output does the brain receive?
15%
What is the oxygen consumption of the brain?
High
20% total body consumption
How do neurones produce ATP?
Almost entirely by oxidative metabolism of substrates including glucose and ketone bodies, little capacity for anaerobic metabolism
How quickly do energy dependent processes cease without oxygen in the brain?
3-8 minutes
Irreversible cellular injury
Name the methods of regulation of cerebral blood flow
Autoregulation (myogenic)
Cerebral metabolism
Carbon dioxide and oxygen
Neurohumoral factors
Describe the myogenic mechanism in autoregulation of cerebral blood flow
vascular smooth muscle constricts in response to an increase in wall tension
For vision the optic tract synapses in the lateral geniculate nucleus.
Where does it synpase in pupil constriction?
Some fibres given off optic tract to pretectal nucleus and onto oculomotor nerve
Why does the pupil fix and dilate in head trauma?
apart from trauma to the orbit
Raised ICP may push temporal lobe over and this will herniate through tantrum cerebellum and will press on the oculomotor nerve
(Uncal Herniation)
What is an Uncal Herniation?
Temporal lobe presses on oculomotor nerve and ipsilateral corticospinal tracts
What is a subfalcine herniation?
Cortex is pushed under falx cerebri
Medial motor corex affected
What is Foramen magnum herniation?
Brain stem centres herniate through foramen magnum
Why does calling an anethetist to enduce hyperventilation help with raised ICP?
Hyperventilation decreases CO2
This is picked up by the carotid body
Bloodflow is reduced
ICP lowers
Why can raised ICP enter a vicious cycle?
- Raised ICP
- Decreased Cerebral Blood Flow
- Tissue hypoxia
- Increased CO2 and decreased pH
- Cerebral vasodilation and oedema
- Raised ICP
What is mannitol?
Osmotic diuretic
Very useful
“Dries out the brain”
What are a neurosurgeons options for interventions in raised ICP?
Craniotomy an ecavuation of clot
External ventricular drainage
Decompressive craniectomy
