LO5 Head and Facial Injuries (Chapter 12) Flashcards
meninges
Fibrous coverings of the brain
Dura mater, arachnoid mater and pia mater
The intercranial volume is composed of
the brain,
the CSF
blood in the blood vessels which completely fill the cranial cavity
Any increase in one of the components is at the expense of the other two
Monro-kellie doctrine
because of the fix space within the rigid skull as a brain tissue swells it takes up more volume
initially with brain swelling, blood and CSF volumes inside the skull decrease and compensate for the rise and pressure
as brain swelling continues compensation fails and intercranial pressure begins to rise
As the ICP increases the amount of blood they can enter the skull and perfused brain decreases leading to further brain injury
what happens when something obstructing the outflow a spinal fluid
Trumatic blood in the vesicles or subarachnoid space will cause an accumulation of spinal fluid within the brain and an increase in ICP
Primary brain injury
is the immediate damage to the brain tissue that is direct result of the mechanical force and is essentially fixed at the time of injury
Most primary brain injuries occur either as a result of external force is applied against the skull or from movement of the brain inside the skull
deceleration head injuries
the head usually strikes in object which causes a sudden discolouration of the skull
the brain continues to move forward impacting first against the skull in the original direction of the motion third collision and then rebounding to hit the opposite side of the inner surface of the skull a fourth collision
Coup
contracoup
Coup: injuries that occur to the brain in the area of the original impact
Contracoup: injuries that occur to the brain on the opposite side
Secondary brain injury
is the result of hypoxia and or decreased perfusion of the brain tissue
In response to the primary insult swelling can cause a decrease in perfusion
result in Vasodilation with increased blood flow to the injured area
No extra space inside the skull swelling of the injured area or newly formed intracerebral haematoma increases intracerebral pressure leading to a decrease cerebral blood flow that causes secondary brain injury
hypoventilation vs hyperventilation
An increase in the level of CO2 hypoventilation promotes vasodilation of vessel supplying the brain whereas lowering the level of CO2 hyperventilation causes vasoconstriction and decreases blood flow to the brain
Intracranial pressure
The pressure within the
skull
increased ICP
Blood supply will be decreased by the increased ICP and because the brain requires a constant supply of blood to survive brain swelling can be rapidly catastrophic
ICP is considered dangerous when it rises above 15 mmHg cerebral herniation may occur at pressures above 25 mmHg
Cerebral perfusion pressure (CPP):
The net pressure gradient causing blood flow through the brain
It’s value is obtained by subtracting the ICP from the MAP
what happens when ICP increases
the system blood pressure increases to try to preserve blood flow to the brain
the body senses the rising systemic blood pressure and this triggers a drop in pulse rate
why does heart rate drop when ICP increases
the body tries to lower the systemic blood pressure by lowering cardiac output
Cerebral perfusion
Pressure required to perfuse brain
You must maintain a CPP of 60 to 70 mmHg which requires maintaining a map of greater than 70 mmHg in the patient with severe TBI
CPP= MAP-ICP
Map constant + ICP increase = CPP Decrease
Map increases + ICP constant = CPP Increase
MAP decrease + ICP increase =CPP critical
map in normal brain vs ICP brain
Map- normal brain 65+= 90/p
Map- increase ICP = 85 110/p
Cerebral Herniation Syndrome
When the brain swelling or intercranial haemorrhage occurs particularly after a blow to the head a sudden rise in ICP may occur and force portions of the brain downward through the tentorium cerebelli
This leads to obstruction of the flow of CSF in the herniated brain apply significant pressure to the brain stem resulting in cerebral herniation syndrome
Cerebral Herniation Syndrome signs and symptoms
a decreasing LOC that rapidly progresses to coma
dilation of the pupils in an outward downward deviation of the eye on the side of injury
paralysis of the arm and leg on the side opposite the injury or dcerebrate positioning,
vital signs revealed increased blood pressure and bradycardia
signs of Increasing ICP
Respirations- increase, decrease, irregular
Pulse- decrease
Blood pressure- increase, widening pulse
Cushings reflex
increase BP
decrease heart rate
irregular resp: Heyne stroke
Hyperventilation
Hyperventilation will decrease the size of the blood vessels in the brain and briefly decrease ICP
Cerebral herniation syndrome is the only situation in which hyperventilation is still indicated
you must ventilate every three seconds and attempt to keep ET CO2 at 30 to 35 mmHg
When to hyperventilate:
after fixing hypoxia and hypotension
- TBI patient with a GCS score less than 9 with extensor posturing (decerebrate)
- TBI patient with a GCS score less than 9 with asymmetric, dilated, or non-reactive pupils
- -Remember hypoxemia, orbital trauma, substances, lightning strike, and hypothermia also affect people every reaction - TBI patient with an initial GCS score less than 9 that then drops his or her GCS by more than two points