L15 - ICP Flashcards
What can causes raised intracranial pressure?
Blood
Tumour
CSF
Brain inflammation
Normal intracranial pressure
Adults - 5 - 17 mmHg
Children - 5- 7 mmHg
Term infants - 1.5 - 6 mmHg
Pressure over 20mmHg is high
How to assess oxygenation and haemodynamics non invasive
NIRS - near infrared spectroscopy
ICP waveform
P1 - arterial pulsation
P2 - brain tissue compliance
P3 - dicrotic wave with aortic valve closure
Acute brain injury waveform
- compliance decreases
- p1:p2 reversed
Monroe - Kellie doctrine
Any increase in the volume of intracranial:
- blood
- CSF
- brain
Must be compensated for by a decrease in the others.
As volume increases, pressure increases exponentially as skull acts as rigid box
Intracranial Monroe - Kellie doctrine
Brain tumour increases the volume of the brain therefore CSF and venous blood are pushed out of the intracranial space as they are at low pressure.
- sum of intracranial volumes remains constant
Cerebral perfusion pressure
CPP= MAP - ICP
Normal - above 70mmHg
Auto regulation of cerebral blood flow
- If mean arterial pressure (MAP) increases, CPP increases which triggers intracranial vasoconstriction to preserve the cerebral blood flow
- If ICP increases, CPP decreases triggering intracranial vasodilation
CPP less than 50 mmHg
Cerebral blood flow cannot be maintained as cerebral arterioles are maximally dilated
If ICP rises enough to cause CPP to decrease below 50 mmHg, ICP will rise exponentially and not compensated for
Why does raised ICP cause death
Brain ischaemia
Brain shifting
Symptoms and signs of raised ICP
Symptoms:
- headaches - constant and worse in the morning and straining
- Diplopia
- nausea and vomiting
- drowsy - and difficulty concentrating
Signs:
- irregular breathing
- decreased heart rate - slow pulse
- hypertension (due to vasodilation)
- Cheyne stokes respiration
- confusion
- non reactive pupils
- loss of consciousness
- papilloedema
Cushing’s reflex
- bradycardia - increased MAP detected by baroreceptors therefore increased vagal activity (can causes stomach ulcers)
- hypertension - vasoconstriction and increase in MAP to compensate for high ICP and maintain CPP
- irregular breathing pattern - compression of brainstem damages the respiratory centres
Causes of raised ICP
Blood:
- malignant hypertension (Rapid high BP that causes organ damage)
- raised venous pressure - SVC obstruction
- haemorrhage
CSF:
- obstructive hydrocephalus E.g aqueduct stenosis
- communication hydrocephalus - too much CSF production
Brain:
- encephalitis
- meningitis
- Reye’s syndrome
Other:
- drowning
- craniosynostosis
Clinical signs of raised ICP
- Bulging head with head circumference increasing more than expected
- sunsetting eyes - direct compression of orbits and occulomotor nerve damage
When is an urgent CT done
GCS below 13
GCS below 14 -2 or more hours after the injury
Neurological abnormalities:
- seizure
- loss of consciousness
- focal neurological deficit
Other:
- suspected skull fracture of basal skull fracture
Management of raised intracranial pressure
- tapping the fontanelle with a needle
- medium term external ventricular drain (allows continuous pressure monitoring)
- long term ventricular shunts
Disadvantages of medium term external ventricular drains
- increased risk of infection as there is a direct communication between the brain and external environment
- inpatient monitoring (not good long term)
When is an external ventricular drain used
When shunt fails or is contraindicated
Ventricular shunts
- Tube placed form the ventricular system to the peritoneum or right atrium
- Has a valve to prevent back flow
- extra length to compensate for child’s growth
How does cerebral oedema cause damage to the brain
Vasogenic - break down of tight junctions
Cytotoxic - damage to brain cells
Osmotic - ECF becomes hypotonic
Interstitial - damage to blood brain barrier and CSF flow into ependyma
Ependyma
Made up of ependyma cells which are a type of glial cell that line the ventricles
Sites of herniation
Subfalcine
Transtentorial
Uncal
Tonsillar
Subfalcine herniation
The cingulate gyrus herniates underneath the falx cerebri
Loss of ventricle on affected side
Can compress the anterior cerebral artery
Uncal herniation
Uncus herniates through the tentorium cerebellum notch compressing CN III and midbrain
- can compress the cerebral peduncle and cause contralateral hemiparesis
Tonsillar herniation
Brain pushed down through the foramen magnum
The cerebellar tonsils can compress the medulla
- Coning
Transtentorial herniation
Central downward herniation
Medial temporal lobe and other midline structures pushed down through the tentorial notch
Management of brain herniation tier 0
- maintains O2 and remove CO2 - maintain airways and breathing
- maintain MAP and CPP - circulatory support
- sedation, analgesics and paralysis - decreases metabolic demand and coughing which would increase ICP
- head up tilt - improves venous drainage
- Temperature - therapeutic hypothermia
- fever control - potent vasodilation
- anti convulsants - prevents seizures to decreases metabolic demand
- nutrition and proton pump inhibitors - prevents stomach ulcers from vagal activity
Tier 1 management
- mannitol (osmotic agent) - osmotic diuresis
- hypertonic saline
- ventricular drainage
- hyperventilation - decrease CO2 which acts as a vasodilator
Tier 3
Barbiturate coma - avoid epilepsy
Hyperventilation
Hypothermia
Decompressive craniectomy
Budd Chiari malformation
Cerebellum is too big
Protrudes down the foramen magnum
Anoxic brai.
Absence of oxygen causes:
- failure of Na+/K+ ATPase
- efflux of K+
- influx of Na+
- depolarisation of neurones
- water follows Na+ influx causing oedema
Mitochondrial anoxia activates nitric oxide synthase producing motor is oxide which is a vasodilator
- toxic oxygen radicals are also produced
