what are the main pathophysiological processes in a case of raised ICP?
haemorrhage - “mass effect”
disruption of blood brain barrier - raised ECF
membrane failure - influx of calcium - cellular swelling
influx of inflammatory mediators
what are some secondary effects of raised ICP?
herniation syndromes
decreased cerebral perfusion
what is the monro kellie doctrine?
volume of: CSF Blood Brain Other cranial contents constitute the volume of the intracranial space and that must remain CONSTANT
what determines the cerebral perfusion pressure?
Mean arterial pressure minus the ICP
what is the normal value of CPP?
80mmHg
what is the normal value for MAP?
90mmHg
what is the normal ICP?
5-15mmHg
what determines the MAP?
diastolic BP plus 1/3 pulse pressure
what type of respiration does the brain use to produce virtually all of its ATP?
aerobic
what happens if the brain is deprived of oxygen?
energy dependent processes cease, leading to irreversible cellular injury within 3-8 minutes
what are some factors that regulate cerebral blood flow?
autoregulation
cerebral metabolism
carbon dioxide and oxygen
neurohumoral factors
what is the response of vascular smooth muscle to an increase in wall tension in blood vessels?
constricts
what cortex is affected in subfalcine herniation?
medial motor cortex
what structures are affected in uncal herniation?
3rd CN
ipsilateral corticospinal tracts
what structures are affected in foramen magnum herniation?
brain stem centres
what drug is given to treat raised ICP?
mannitol
how is a patient with raised ICP managed in ITU?
head position - 30 degress up nothing to impede venous drainage CO2 maintained in low normal range intermittent boluses of mannitol when ICP raised fully sedated and paralysed
why is the pupil fixed and dilated in head trauma?
compression of the parasympathetic supply to the eye (edinger westphal nucleus of oculomotor nerve and disruption of the ciliary ganglion) leads to uncontested sympathetic innervation