Raised ICP Flashcards
What is the normal ICP?
5 to 15 mmHg
What signs and symptoms are associated with raised ICP?
Headache Vomiting - N&V progresses to projectile Visual disturbance Reduced level of consciousness Evolving focal neurology Subtle personality change
Describe the headache typically seen with raised ICP
Generalised ache
Worse on waking in morning - due to hypoventilation during sleeping hours
May wake patient from sleep
Aggravated on bending, stooping, lying down
Aggravated by coughing or sneezing (increasing intrathoracic pressure - preventing venous return from head)
Severity gradually progresses
What visual disturbance is seen with raised ICP?
Blurring
Obscurations - transient blindness upon bending or posture change
Papilloedema
Retinal haemorrhage if rise has been rapid
What is papilloedema?
Optic disc swelling due to raised ICP of any cause.
The optic nerve is part of the CNS - it has CSF around it, so raised ICP is transmitted to the nerve.
Why is cranial nerve VI often affected?
Has a long course and runs close to the skull.
Innervates lateral rectus- abducts the eye
What is a subfalcine herniation?
When the brain tissue is displaced under the falx cerebri
What are some characteristics of a subfalcine herniation?
Most common type
May be asymptomatic
Symtoms: headache, contralateral leg weakness if anterior cerebral artery affected
Midline shift on CT
What is an uncal herniation?
When the medial part of the temporal lobe is displaced across the tentorial opening
As an uncal herniation progresses, it puts pressure on what part of the brainstem?
Midbrain
Function: eye movement and reflex responses to sound and vision
Projection fibres pass through
Contains CN III and IV nuclei
What signs can be see with uncal herniation?
Damage to CNIII - ipsilateral dilated pupil
Compression of ipsilateral cerebral peduncle (contain sensory and motor tracts) - contralateral leg weakness
LOC
Signs may be false localising if midbrain pushing against opposite side of tentorium
What is tonsillar herniation?
When the cerebellar tonsils herniate through the foremen magnum
What symptoms and signs are associated with tonsillar herniation?
Compression of medulla - cardiac and respiratory dysfunction
LOC (RAS disturbance)
Lower CN dysfunction
Typically rapidly fatal
If raised ICP is not treated and continues to rise, what reflex can occur?
Cushing’s reflex
Why does Cushing’s reflex occur?
Last effort to perfuse the brain
What is Cushing’s triad?
High BP
Bradycardia
Low respiratory rate
(Opposite to sepsis)
Why do you get low respiratory rate in Cushing’s reflex?
Ischaemia to pons/ medulla damages respiratory centres
Why do you get bradycardia in Cushing’s reflex?
Ischaemia at medulla causing sympathetic activation, which elevates BP and HR. Baroreceptors react to this causing bradycardia
What are some causes of raised ICP?
Expanding mass: Tumour - primary or mets Abscess Haemorrhage/ haematoma Cyst
Cerebral oedema: Meningitis Encephalitis Diffuse head injury Infarction
Increased cerebral blood volume:
Venous outflow obstruction
Venous sinus thrombosis
Increased CSF:
Impaired absorption - hydrocephalus, benign intracranial hypertension
Excessive secretion - choroid plexus papilloma
Does CSF contain a lot or a small amount of protein?
Small amount
Compared to plasma, is CSF hyper or hypo osmolar?
Hyperosmolar (more sodium)
What is raised ICP most commonly due to?
Trauma
What is hydrocephalus?
An accumulation of CSF due to imbalance between production and absorption, causing enlargement of the brain ventricles
What are the 2 classifications of hydrocephalus?
Non communicating/ obstructive - CSF obstructed within ventricles or between ventricles and subarachnoid space
Communicating - there is communication between ventricles and subarachnoid space, the problem lies outside ventricular system or too much CSF production.
Obstructive hydrocephalus is most commonly due to aqueduct blockade. What can cause this?
Congenital or acquired e.g meningioma
What is idiopathic intracranial hypertension?
Raised ICP without evidence of mass or hydrocephalus
Normal imaging results, but signs of raised ICP
Who does idiopathic raised ICP normally affect?
Obese young women after weight gain
What is a common presentation of idiopathic raised ICP?
Narrowed visual fields Blurred vision CN VI palsy Enlarged blind spot if papilloedema present Consciousness preserved and cognition
How is idiopathic raised ICP treated?
Weight loss
CSF drainage (e.g therapeutic LP) and shunts
Carbonic anhydrase inhibitors
What are the principles of management for raised ICP?
Shunts
Tumour resection
Diuretics while awaiting intervention
If cerebral oedema: mannitol, hypertonic saline, dexamethasone
What test should be avoided?
LP avoid before imaging as risk of coning
What imaging should be done?
CT +/- MRI
Cerebral perfusion pressure=
Mean arterial pressure (MAP) - intracranial pressure
If intracranial pressure is high, the only way the body can compensate to increase CPP is by increasing MAP
(MAP= SPB+2(DBP) /3
A sympathetic reflex result I’m hypertension. A counter parasympathetic reflex occur by stimulation of the baroreceptors - bradycardia
