S10) Pathophysiology and Management of Raised Intracranial Pressure Flashcards
What is normal intracranial pressure?
Normal ICP = 5–15 mm Hg (7–20 cm H2O)
5-7 in children
which two components normally change to maintain the Brain Vol
CSF and venous blood since they are at the lowest pressure
What are the occupants of intracranial space?
- CSF (10%)
- Blood (10%)
- Neural tissue (brain + spinal cord) (80%)
In a healthy individual, the blood flow to the brain is regulated.
Explain how this occurs by autoregulation and chemo-regulation?
- Autoregulation – vasoconstriction, vasodilation
- Chemo-regulation – vasodilation in response to low cerebral pH e.g. high pCO2
Illustrate the intracranial compensation for an expanding mass
In four steps, illustrate the pathophysiology of a brain injury
Identify four signs of symptoms of raised intracranial pressure
- Headache
- Vomiting
- Visual disturbances
- Depression of conscious level
- seizures
Describe five characteristics of a headache due to raised ICP
- Generalised ache
- Worst on awakening in the morning
- May awaken patient from sleep (due to hypoventilation in sleep)
- Aggravated by bending, stooping, coughing or sneezing
- Severity gradually progresses
Describe four characteristics of visual disturbances due to raised ICP
- Blurring
- Obscurations – transient blindness upon bending or posture changes
- Papilloedema (some patients)
- Retinal haemorrhages (if rapid ICP rise)
Identify two red flag signs of raised ICP
- Papilloedema
- CN VI palsy – false localising sign
and blown dilated pupil due to compression of oculomotor nerve
Describe the occurrence and presentation of a subfalcine herniation
- Most common
- May be asymptomatic
- Symptoms incl. headache, contralateral leg weakness (if, ACA affected)
- Midline shift on CT
→ cingulate gyrus is pushed under the free edge of the falcs cerebri which can compress the anterior cerebral artery as it loops over the corpus callosum
What is an uncal herniation?
An uncal herniation is when the uncus, the medial part of the temporal lobe, is displaced across the tentorial opening
→ Uncus of temporal Lobe herniates through tentorial notch compressing adjacent midbrain = 3rd nerve palsy → contralateral hemiparesis
As the herniation progresses, the uncus puts pressure on the midbrain.
Describe the different possible presentations of uncal herniations
- Decreased level of consciousness
- Compressed ipsilateral oculomotor nerve – ipsilateral dilated pupil
- Compressed cerebral peduncle – contralateral leg weakness
What is a tonsillar herniation?
A tonsillar herniation is when the cerebellar tonsils herniate through the foramen magnum compressing medulla
Explain the presentations of tonsillar herniations?
Compression of medulla and upper spinal cord:
- Brainstem affected – cardiac and respiratory dysfunction
- Decreased level of consciousness
what is a central downward herniation
→ medial temoral lobe / other midline structures pushed through the tentorial notch
What is Cushing’s reflex?
- Cushing reflex is a physiological nervous system response to untreated raised ICP
- It is a poor prognostic sign consisting of the following triad: high BP, bradycardia, low RR
In five steps, explain how bradycardia and hypertension occur due to raised ICP
⇒ Ischaemia at medulla
⇒ Sympathetic activation
⇒ Rise in blood pressure & tachycardia
⇒ Baroreceptors react
⇒ Bradycardia
In two steps, explain how hypoventilation occur due to raised ICP
⇒ Ischaemia at pons/medulla at respiratory centres
⇒ Low respiratory rate
Identify and describe the four causes of raised intracranial pressure
- Increased cerebral blood volume – venous outflow obstruction, venous sinus thrombosis
- Cerebral oedema – meningitis, encephalitis, diffuse head injury, infarction
- Increased CSF – impaired absorption (hydrocephalus), excessive secretion (choroid plexus papilloma)
- Expanding mass / SOL – abscess, tumour, haematoma
What leads to the clinical suspicion of raised ICP?
- Traumatic brain injury (haemorrhages, anticoagulants)
- Severe meningitis encephalitis
- Risk factors, signs and symptoms of cancer
- CVS risk factors
Describe the composition and appearance of cerebrospinal fluid
- Normal CSF is clear and colourless
- It contains very little protein (15 to 45 mg/dL), little immunoglobulin, and only 1-5 cells (leukocytes) per ml
- It is hyperosmolar compared to plasma