Head Trauma Flashcards
What is the primary goal of treatment for patients with suspected TBI?
Prevent secondary brain injury
-ensure adequate oxygenation and maintain BP enough to perfuse the brain
True or false: scalp lacerations can result in major blood loss, hemorrhagic shock, even death.
True!
What are the 3 layers of the meninges?
DAP
- Dura
- Arachnoid
- Pia
* *Dura and arachnoid are NOT firmly adhered to each other so bleeding can occur in this space = subdural hemorrhage
* *Arachnoid and pia are also not firmly adhered to each other so bleeding can also occur in this space = subarachnoid hemorrhage
* *Pia is firmly adhered to the surface of the brain
Where are meningeal arteries located?
Between the skull and the dura = this is the epidural space
What is the most commonly injured meningeal vessel?
-where is it located?
Middle meningeal artery - most common site of bleeding in an epidural hematoma
-located beneath the temporal bone: temporal bone fractures can cause laceration of the middle meningeal artery and lead to epidural hematoma
Where are epidural hematomas located?
Between the skull and the dura
Where are subdural hemorrhages located?
Between the dura and the arachnoid
What are two potential sources of bleeding in epidural hematomas?
- Meningeal arteries (most commonly middle meningeal artery)
- Dural sinuses (this is venous bleeding so expands more slowly and puts less pressure on the underlying brain)
What is the source of bleeding in a subdural hematoma?
Bridging veins that lie between the dura and the arachnoid mater
Where are subarachnoid hemorrhages located?
Between the arachnoid and pia mater
What are the 3 parts of the brain?
- Cerebrum: made up of right and left hemispheres, separated by the falx
- Cerebellum
- Brainstem
What are the responsibilities of each of the following areas of the brain:
- frontal lobe
- temporal lobe
- parietal lobe
- occipital lobe
- Frontal lobe: emotions, executive functions, motor function, speech
- Temporal lobe: memory functions
- Parietal lobe: spatial orientation and directs sensory function
- Occipital lobe: vision
What are the 3 components of the brainstem?
-function?
- Midbrain
- Medulla
- Pons
- **Midbrain and upper pons: reticular activating system responsible for state of alertness
- medulla: vital cardiorespiratory centers
What is the function of the cerebellum?
Coordination and balance
What is the pathophysiology of a “blown pupil”?
Oculomotor nerve (CN 3) runs along the edge of the tentorium: if it becomes compressed against the tentorium during temporal lobe herniation, PARASYMPATHETIC FIBERS that constrict the pupils lie on the surface of CN 3 also become compressed and can no longer constrict the pupil. Thus you have unopposed sympathetic innervation of the pupil and get pupil dilatation (“a blown pupil”)
- **in COMPRESSION of CN3, you get impaired pupillary constriction since the parasympathetic fibers are on the surface of the nerve
- **In ISCHEMIA of CN3, you get impaired extraocular movements since the inner fibers of CN 3 control extraocular movements and the blood supply affects the inner fibers first
What are the functions of CN 3?
- Pupillary constriction
- Extraocular movements - innervates superior rectus muscle, (looking up), inferiour rectus muscle, medial rectus muscle
- Eyelid opening (remember the 3 greek columns that hold up the eye)
What is the tentorium?
Tentorium is a tough meningeal partition that separates the brain into the supratentorial component and infratentorial component
-the midbrain passes through an opening called the tentorial notch
Which part of the brain usually herniates through the tentorial notch in head trauma?
-what are the 2 classic signs of uncal herniation?
The medial part of the temporal lobe (known as the uncus) is usually what herniates through the tentorial notch
- uncal herniation causes compression of the corticospinal tract in the midbrain so you can CONTRALATERAL HEMIPARESIS
- you also get compression of the CN 3 in the midbrain so you get IPSILATERAL PUPILLARY DILATATION
- also get compression of the reticular system resulting in decreased GCS
- **Two classic signs of uncal herniation:
1. Ipsilateral pupillary dilatation
2. Contralateral hemiparesis
What is the most common cause of uncal herniation?
Lesion of the middle meningeal artery secondary to temporal bone fracture causing a temporal epidural hematoma
-uncus compresses the upper brainstem = decreased GCS (from compression of the reticular system in the midbrain), ipsilateral pupillary dilatation (from compression of the CN 3 in the midbrain), and contralateral hemiparesis (from compression of the motor tract at the midbrain)
What is the Monro-Kellie doctrine?
The total volume of intracranial contents MUST remain constant since the cranium is a rigid container incapable of expanding
- when the normal intracranial volume is exceeded, ICP rises
- Venous blood and CSF can be compressed out of the container providing a degree of pressure buffering
- Thus, very early after injury, a mass such as a blood clot can enlarge while the ICP remains relatively the same since the body is compensating by pushing out venous blood and CSF from the intracranial compartment
- However, once the limit of displacement occurs, ICP rapidly increases and can cause brainstem herniation or uncal herniation and result in reduction or cessation of cerebral blood flow
What are the intracranial contents?
- Brain
- Venous blood
- Arterial blood
- CSF
- **Once you add a mass such as blood/tumor, you have to get rid of something to maintain normal ICP: usually this is venous blood and CSF that the body tries to dump out of the intracranial contents
- as the mass gets bigger, the brain runs out of venous blood/CSF to dump out and then you get increased ICP
What is the equation for cerebral perfusion pressure?
CPP = MAP - ICP
***normal CPP may help improve cerebral blood flow (CBF) but CPP does NOT equate with or ensure adequate CBF.
What does CO2 do to your brain? What does it do to your lungs?
- CO2 in the brain causes vasodilation = increased blood flow
- CO2 in the lungs causes vasoconstriction = decreased blood flow (you want to shunt your blood AWAY from areas with high CO2 and towards areas that are actually being ventilated)
What are the goals in maintaining cerebral perfusion and limiting secondary brain injury in a head injury patient?
Maintain a normal MAP and reduce your ICP!
- Ensure adequate oxygenation
- Ensure normal CO2 (avoid hypercapnea, hypocapnea)
- Ensure normothermia
- Treat seizures as this increases brain oxygenation consumption
- Avoid hypotension - ensure adequate perfusion to maintain a normal MAP
- Try to evacuate any blood that could be increasing your ICP