WEEK 1 - Acute Cerebral Injury Flashcards
How much of cardiac output does the brain receive?
20% (800-1000mL)
Which gas is the primary regulator of cerebral blood flow?
CO2 (also controls pH)
Which three organ work together to ensure the brain has adequate blood flow all the time?
Brain, heart and lungs
What makes up cerebral blood flow (CBF)? (equation?)
CBF = CPP/CVR,
CPP - cerebral perfusion pressure
CVR - cerebral vascular resistance
What makes up vascular resistance? (3 parts)
- Vessel diameter
- Vessel length
- Blood viscosity
What can CBF be affected by?
- Metabolism - PaO2, PaCO2, pH
- BP (cardiac function)
- Blood viscosity
What is CBF autoregulation?
Brain’s intrinsic ability to maintain a constant CBF despite marked changes in systemic BP through vessel constriction and dilation
What are the parameters within which CBF aims to keep MAP?
60-140 mmHg
What is pulse pressure?
Recoil of an artery following the heart beat
Causes of acidosis?
- Increased CO2
- Decreased O2
- Increased H+
- Decreased pH
Causes of alkalosis?
- Decreased CO2
- Increase of pH
Equation to form H+?
CO2 + H2O = H2CO3 (carbonic acid) = dissociates to form H+
Names of all the ventricles in the brain?
Lateral ventricles (left and right), third ventricle and fourth ventricle
What is contained in the ventricles and where is it made?
CSF in the ventricles
Made by the choroid plexus (lies in the lateral ventricles)
Describe the pathway CSF takes through the brain
Choroid plexus - lateral ventricles - interventricular foramen of Monro - 3rd ventricle - cerebral aqueduct - 4th ventricle - subarachnoid space - absorption via subarachnoid villi - venous blood
What is intracranial pressure (ICP?)
The pressure exerted by CSF that circulates around the brain and into the ventricles
What proportions of the cranial volume do CSF, blood and brain tissue make up?
- CSF = 10%
- Blood = 10%
- Brain tissue = 80%
What is ICP determined by?
Changes in intracranial blood volume and changes in pressure exerted by CSF that circulates around the brain, spinal cord and ventricles
Why is ICP talked about as a RANGE of pressures and not as a single pressure?
Because ICP is in reference to atmospheric pressure = different areas of the brain vary in their pressures
What is the ICP reference range?
5-10 mmHg though 15 is considered the upper limit of the norm
What is a burr hole and when/why would this be used?
Burr hole - small hole drilled into the cranium
This would be used when ICP is elevated - holes help to relieve the pressure and let it out
What is the CPP of an adult?
80 mmHg
Equation for CPP?
CPP = MAP - ICP
If the volume of one component of the cranium is increased, the others must decrease to compensate. What happens if this doesn’t occur?
Compliance of the brain is exhausted and ICP rises - also supercedes the ability of the brain to regulate CPP
How does chronic hypertension change MAP?
resets the upper limit of MAP to 180-200 mmHg
Name the three layers of the meninges?
Dura Mater
Arachnoid Mater
Pia Mater
What is the role of the meninges?
Meninges help maintain CSF, allow for brain compliance within the skull and protect the brain
What is the Monro-Kelli hypothesis
The cranium is a rigid structure, therefore the volumes that make up its contents must remain constant, otherwise an increase in one volume must be compensated by a reciprocal decrease in another
In what context is cerebral oedema most common?
Inflammation of the brain
What is cerebral oedema?
An increase of the fluid content of the brain, or an increase in the extra/intracellular fluid surrounding the brain
May be localised or generalised
What is the most common form of cerebral oedema?
Vasogenic Oedema
Clinical manifestations of vasogenic oedema?
- Altered consciousness
- Neurological deficits
- ‘Tight brain’
Describe the pathophysiology of vasogenic oedema?
Junctions between endothelial cells of capillaries and astrocyte feet become loose = allows fluid and plasma proteins to move out of the vessel and into extracellular spaces
What is cerebral herniation?
Movement of brain matter during stage 4 ICHTN from an area of high pressure to an area of low pressure
Pressure on the herniated tissue increases with an increase in intra-cranial volume, leading to decreased blood flow to that tissue
Neurological signs of early herniation?
Confusion, irritability, headache
What is the tentorium?
Membranous cover within the cranium formed by the dura mater
What type of herniation compresses the brain stem?
Uncal herniaton - hernation of the innermost portion of the temporal lobe or hippocampal gyrus downwards towards the tentorium due to expansion of one hemisphere
What is central herniation?
Downward shift of the diecephalon down towards the mouth
What is tonsilar herniation?
Herniation through the foramen magnum
What three types of herniation have the potential to herniate through the eye cavities?
- Uncal
- Central
- Cingulate gyrus
What drug is given for raised ICP (vasogenic oedema) and what is its mechanism of action?
Mannitol IV - draws water out of tissues and into the vascular system through increasing plasma osmolality
What is the primary goal of treatment for a traumatic brain injury?
Prevention or minimisation of a secondary injury eg. oedema or heriation
What is a contusion?
Bruising of the brain due to blood leakage as a result of small tears in blood vessels caused by blunt or penetrating trauma
What determines the severity of a contusion?
The amount of energy or force transmitted by the skull to the brain tissue by trauma
What is a haematoma?
A bleed in the brain where clots may form and impinge on brain tissue
When blood is not resorbed = irritation to the brain
What is a subdural haematoma and how is it caused?
Bleeding of the brain between the dura and arachnoid mater.
Caused by the tearing of bridging veins located over the convexities of the brain, may be due to skull fracture (falls, alcohol abuse)
What is an epidural haematoma and how is it caused?
Bleeding of the brain between the periosteum and the dura mater
Most are due to a tear in the middle meningeal artery, caused by MVAs, falls, sporting accidents
What is an intracerebral haematoma?
Bleeding of the brain within the brain parenchyma
Is it easier to predict outcomes for diffuse or focal brain injuries? Give a reason why
Focal - this is because focal injuries impact smaller areas of the brain
What is a diffuse axonal injury?
Widespread axonal damage commonly associated with acceleration/deceleration causing stretching or tearing of nerve fibres
What characterises a mild concussion?
Temporary axonal disturbance WITHOUT loss of consciousness
What characterises a classic concussion?
Cerebral disconnection from the brainstem reticular system, causes IMMEDIATE loss of consciousness lasting for less than 6 hours
Causes altered RR, decreased BP and HR
What is meningitis?
Infection and inflammation of most commonly the pia mater and arachnoid mater but can also affect the dura mater
What are the risk factors for meningitis? (x4)
Age <5 and >60 years, immunosuppression, communal living, splenectomy
What are the 4 known causes of meningitis?
- Bacteria
- Fungi
- Parasites
- Viruses
What pharmacological treatment is used for meningitis?
- Antibiotics - eg. benzylpenicillin, cephtriaxone, vancomycin, ampicillin
- Dexamethosone
