2.3 CNS Complications: Intracranial Pressure Flashcards
The leading cause of death after TBI and stroke is…
Cerebral oedema
The mortality of malignant cerebral oedema is in excess of…
60-80%
Name the two mechanisms of cerebral oedema
- Vasogenic oedema
- Cytotoxic oedema
Explain the mechanism of vasogenic cerebral oedema
- BBB increases permeability in response to damage
- Proteins (e.g. albumin) enter brain
- Water follows gradient, increase EXTRAcellular volume.
Describe the mechanism of cytotoxic cerebral oedema
- Increased fluid inside brain cells
- Often caused by failure of ion pumps
- Increase in brain volume
True or false: the two main mechanisms of cerebral oedema usually occur in conjunction with one another
True
How do we calculate cerebral perfusion pressure?
CPP = Arterial pressure - ICP
If MABP = ICP, no perfusion to the brain
What is it called when the brain tries to regulate ICP in response to some kind of mass?
Spatial compensation
Describe the brain’s two mechanisms of spatial compensation
- Shunt off CSF (increase resorption, decrease production)
- Venous vasoconstriction
Describe the “desperate” arterial response in spatial compensation in the brain
- Arterial vasonstriction
(But then the brain runs out of breath)
- Arterial vasodilation; re-establishes blood flow, but increased ICP
Describe the fundamental positive feedback loop of ICP decompensation
- Increased ICP
- Decreased CPP
- Decreased blood flow to cerebrum
- Ischaemia > tissue injury
- More oedema raises ICP
- Hypercapnia (from low blood flow) causes further vasodilation andthus inc. ICP
List the three main kinds of brain herniation
- Subfalcine (falx cerebri)
- Transtentorial/uncal
- Tonsillar (foramen magnum)
What is the most common kind of brain herniation?
Subfalcine
Symptoms of subfalcine hernation
- Coma
- Increased ICP (blocked blood vessel?)
- Cerebral oedema
What is the characteristic symptom of uncal herniation?
Inability of pupil to dilate/respond to light
How do hyperosmotic agents reduce ICP?
- Increased blood osmolarity
- Draw water from brain into blood
- Decreased cerebral oedema
How do barbituates lower ICP?
- Suppress cerebral metabolism
- Decreased blood flow to brain due to decreased demand
- Decreased production of metabolic byproducts that lead to cerebral oedema
How do steroids reduce ICP?
Inhibit inflammatory response (and therefore oedema)
What kinds of drugs can be used to treat raised ICP?
- Hyperosmotics
- Barbituates
- Steroids
What surgical interventions are available for raised ICP?
- Decompressive craniectomy
- Ventricular drain
At what ICP level should clinical intervention occur?
> 20mmHg
Describe the three-tiered management of raised ICP
Tier 1: CSF drainage, slight hyperventilation
Tier 2: Mannitol/hypertonic saline, hyperventilation
Tier 3: Barbiturates, craniectomy/hypothermia
SMB = Super Mario Brothers = Surgery, Mannitol, Barbituates
When trying to reduce intracranial pressure, the head should be tilted up by __ degrees.
30°
Why is an intact BBB required for mannitol therapy in ICP reduction?
If mannitol gains access to the brain, then water will flow into the brain, having the opposite effect.
List some basic side effects of mannitol
- Rebound ICP levels
- Allergic reaction
- Heart failure
List two obvious possible side effects of hypertonic saline administration
- Hypervolemia
- Electrolyte imbalance
What are the purported mechanisms of action for steroids in ICP reduction?
- Reduce BBB permeability
- Free radical scavenging
Does the onset of effects from corticosteroids happen immediately, or is it slower? Why?
- Slower
- Effect is upstream of protein synthesis (steroid = enters nucleus and affects transcription)
What are some short term adverse effects of corticosteroids?
Glucocorticoid: inc. blood glucose, nervousness
Mineralocorticoid: fluid retention, hypokalaemia, increased BP
Corticosteroids can be stopped suddenly as long as they’ve been taken for less than…
4 weeks
Can you start a patient on long-term corticosteroids straight away?
- No
- Start on initial trial, wait for adverse effects, then consider long-term prescription
What are some long-term adverse effects of corticosteroids?
- Osteoporosis
- Growth retardation
- Poor wound healing
On imaging, what are the three most important causes of ventricular enlargement?
- Cerebral atrophy
- Hydrocephalus
- Encephalomalacia
How can subfalcine herniation cause cerebral infarct?
- ACAs run in longitudinal fissure
- Get compressed by haemorrhage
- Infarction
Describe the density of blood relative to brain tissue acutely, subacutely, and chronically
Acute: Hyperdense (bright)
Subacute: Isodense (same)
Chronic: Hypodense (darker)
Describe traumatic contusions as a class of intra-axial haemorrhage
Cortical haemorrhage in response to impact against skull
How does diffuse axonal haemorrhage present on CT?
Small haemorrhages at grey-white juncture -> often need MRI for further investigation as this is a severe injury
What does a haemorrhagic transformation look like on CT?
- Established, more hypodense region of infarct
- Hyperdense region of haemorrhage within
What is the most common cause of lobar haemorrhage
Amyloid angiopathy
How does cerebral oedema show up on CT?
Loss of grey-white differentiation; regions of hypodensity.
