Pathophysiology Of Raised Intracranial Pressure Flashcards
Intracranial pressure range in adults
5-15mmHg
Intracranial pressure range in children
5-7mmHg
Intracranial pressure range in term infants
1.5-6mmHg
What is intracranial pressure determined by?
Volume of blood
CSF
Brain
What is Monro-Kellie doctrine hypothesis?
Any increase in the volume of one of the intracranial constitutes must be compensated by a decrease in the volume of one of the others
What are the first components to be pushed out of the intracranial space when there is an intracranial mass?
CSF
Venous blood
Cerebral perfusion pressure calculation
CPP = mean arterial pressure - ICP
What can cause raised ICP?
Too much CSF, blood or brain
What is hydrocephalus?
Build up of CSF within the brain
Management of hydrocephalus
- acutely by tapping fontanelle with needle
- medium term drainage by external ventricular drain
- long term by ventricular shunts: tube between ventricular system + peritoneum or right atrium
Clinical signs of hydrocephalus
- bulging head with head circumference increasing faster than expected
- sunsetting eyes
Acquired causes of hydrocephalus
- meningitis
- trauma
- haemorrhage e.g. post subarachnoid haemorrhage
- tumours e.g. compressing cerebral aqueduct
What is cerebral blood flow dependent on?
When can it not be maintained?
Cerebral perfusion pressure
If CPP <50mmHg
Outline cerebral auto regulation in regards to mean arterial pressure + ICP
- if MAP increases > CPP increases > triggers cerebral autoregulation > vasoconstriction of cerebral arterioles
- if ICP increases > CPP decreases > triggers cerebral auto regulation > vasodilation of cerebral arterioles
Outline Cushing’s triad/response/reflex
- rise in ICP > hypertension as body increases MAP to maintain CPP
- increase in MAP > detected by baroreceptors > bradycardia via increased vagal stimulation
- continuing compression of brain steam leads to damage to respiratory centres > irregular breathing
Four major pathophysiologies of cerebral oedema
- vasogenic
- cytotoxic
- osmotic
- interstitial
***
Clinical features of raised ICP
- constant headache which worsens on bending/straining + in morning
- N + V
- double vision
- visual field defects
- papilloedema
- seizures
- reducing GCS - confusion, drowsiness, unconscious
- focal neurological signs
Epidemiology idiopathic intracranial hypertension
obese middle aged females
Diagnosis of idiopathic intracranial hypertension
Confirmed by raised opening pressure on lumbar puncture
Treatment of idiopathic intracranial hypertension
Weight loss
Blood pressure control
Types of brain herniation
- tonsillar herniation (coning)
- uncl herniation
- subfalcine hernation
- central downward herniation
- external herniation
Outline tonsillar herniation (coning)
Cerebellar tonsils herniate through foramen magnum > compression of medulla
Outline subfalcine herniation
Cingulate gyrus herniates under free edge of Falx cerebri > compression of anterior cerebral artery as it loops over corpus callosum
What is vulnerable in a subfalcine herniation?
Anteior cerebral artery as it loops over corpus callosum
Outline uncl herniation
- Uncus of temporal lobe herniates through tentorial notch > compresses adjacent midbrain
- can cause oculomotor nerve palsy + blown pupil
- can cause contralateral hemiparesis due to compression of cerebral peduncle
Outline central downward herniation
Medial temporal lobe + other midline structures pushed down through tentorial notch
Outline external herniation
Brain herniation through skull fracture or therapeutic craniectomy
What is Cushing’s triad?
Hypertension
Bradycardia
Irregular breathing
Management of a patient with acutely raised ICP
- maintain O2 + remove CO2
- maintain MAP > maintains CPP
- sedation, analgesia + paralysis: decreases metabolic demand + prevents coughing + shivering that might increase ICP more
- elevate head of bed 10-15°: maximises cerebral venous return
- prevent hyperthermia
- anticonvulsants
Ongoing management of raised ICP
- osmotic diuresis: e.g. mannitol or hypertonic saline
- regular re-evaluation + monitoring
- surgical intervention: evacuation of haemorrhage, ventricular drainage, evacuation of haemorrhage
Examples of surgical intervention of raised ICP
- evacuation of haemorrhage
- ventricular drainage
- decompressive craniectomy
Generally what is classed as high ICP?
> 20mmHg
If a patient has hypertension + raised ICP, why should you not attempt to lower it?
May be directly driving perfusion to ischaemic areas of brain
Why can hydrocephalus cause sunsetting eyes?
Direct compression of orbits + oculomotor nerve as i exits midbrain