Cerebrovascular issues Flashcards
What is intracranial pressure?
-The pressure exerted within the rigid skull and meninges by the brain matter (80%), cerebral spinal fluid (10%), and the amount of cerebral blood flow (10%)
-normal range for adults is 0-15mmHg
What is the mono-kellie hypothesis?
-the volume of the brain, CSF, and intravascular blood remains nearly constant in a state of dynamic equilibrium
-if any one compartment increases in overall volume, another compartment must decrease for the overall volume and dynamic equilibrium to remain constant, otherwise inter cranial pressure will rise
What are the 4 compensatory mechanisms for ICP?
-increased CSF absoprtion
-decreased CSF production
-shunting of CSF to the spinal space
-vasoconstriction, reducing cerebral blood volume
What is cerebral blood flow?
-essential for the supply of oxygen, glucose and nutrients to the cerebral tissues
-a critical relationship exists between CBF and ICP- CBF being disadvantaged in the presence of raised ICP
What is cerebral perfusion pressure? and how is it calculated?
-the pressure required to maintain an adequate cerebral blood flow
-calculated by Mean Arterial Blood Pressure (MAP) - ICP
-acceptable CPP is 50-70mmHg
List the signs and symptoms of raised ICP
-disorientation
-irritation
-decrease in conscious level
-headache
-pupillary abnormalities
-visual disturbances
-aphasia
-seizures
-motor dysfunction
-nausea and vomiting
-changes in respiratory pattern
-changes in vital signs
what is the crushing’s Triad?
a set of signs that indicate increased ICP in the brain
-increased blood pressure
-decreased heart rate
-decreased respiratory rate and change in respiratory pattern
How is raised ICP managed?
-maintaining optimum cerebral perfusion pressure
-maintain ICP below 20mmHg
-provide oxygen and glucose
-maintain cardiorespiratory stability
What is the circle of Willis?
-a blood ‘roundabout’ in the brain, with many arteries branching off, including the posterior cerebral artery, middle cerebral artery, and the anterior cerebral artery
-important because if there is damage in one part of the brain, blood can still get to this area
-AVMs may occur in children, blood is shunted straight from arteries to veins, and the high arterial pressure causes veins to burst
What are venous sinuses?
a network of blood channels that drain deoxygenated blood from the brain to the heart
What is autoregulation?
the ability of an organ to maintain a constant blood flow rate despite changes in arterial pressure
What is an inter cranial haemorrhage, and what are the 2 main types?
-a brain bleed
-can either be extra-axial= occurring outside of the brain tissue
-or intra-axial= occurring within the brain tissue
What is an epidural extra-axial haemorrhage?
-bleed occurs between the skull and the dural membrane
-results from head trauma e.g car accident
-clinical manifestation= altered consciousness, headache, vomiting, confusion, seizures, aphasia
What is a subdural extra-axial haemorrhage?
-bleed occurs between the dura matter and the arachnoid membrane
-results from head trauma
-clinical manifestation= 50% have a coma
What is a subarachnoid extra-axial haemorrhage?
-bleed occurs in subarachnoid space
-results from cerebral artery aneurism
-clinical manifestation= severe, sudden headache, loss of consciousness, nausea, vomiting, seizures
What is an intracerebral intra-axial haemorrhage?
-second most common cause of strokes
-results from hypertension, embolism, brain tumour, bleeding disorders, drug use
-clinical manifestations= neurological signs, headaches, nausea, vomiting, decreased consciousness
What is an intraventricular intra-axial haemorrhage?
-bleeding occurs within ventricle system in brain
-most often occurs as a secondary phenomenon to other inter cranial haemorrhage
What is a brain herniation and what is the cause?
-when brain tissue moves outside of the skull, or moves into a structure within the skull
-typically occurs in response to increased intracranial pressure (above 15mmHg)
What is a mass effect and how does this relate to ICP and brain herniation?
-a mass effect increases intracranial pressure, so less CSF is produced and more is reabsorbed, = brain herniation
-can be focal mass effect e.g intracranial bleeds, tumours causing local oedema
-or diffuse mass effect e.g generalised cerebral oedema, cryogenic oedema (within cells= retention of sodium and water)
What is a supratentorial herniation? What are the 4 types
-displacement of the cerebrum
1. uncal herniation
2. central herniation
3. singular herniation
4. transcalvarial herniation
What is an infratentorial herniation? What are the 2 types
-displacement of the cerebellum
1. upward herniation (displacement of cerebellum upwards)
2. tonsillar herniation (cerebellar tonsils slip down through foramen magnum)
What is hydrocephalus?
a condition that involves the build up of cerebrospinal fluid (CSF) produced in the ventricles, which can be congenital or acquired
What are the 3 ways a build of CSF can occur?
- excess production of CSF
- impaired reabsorption of CSF
- blockage in ventricular system
What is the difference between communicating and non-communicating hydrocephalus?
communicating= no blockage in ventricular system
non-communicating= blockage in ventricular system (the most common)
What is a major difference in children and adults with hydrocephalus?
-in infants, the skull is more capable of expanding so head is enlarged, but there is more time before the onset of other symptoms
-in adults, the skull isn’t able to expand and symptoms may appear more quickly
How can hydrocephalus be treated?
attempt to drain the excess CSF, done using a shunt (a plastic tube connected to a catheter) where CSF is diverted to abdominal cavity where it can safely drain
