Neuro #1 Flashcards
Pia Mater
Thin cerebral cortex cover, similar to the outside of a grape.
Arachnoid Membrane
- CSF location = subarachnoid space
- between arachnoid and Pia matter
- CSF is created 500 mL every day replaces whole CSF fluid three times a day.
Dura matter outermost layer
Tough outer covering that is adhered very tightly to skull
- requires pliers for separation
- very high pressure is required for bleeding to occur (arterial)
- causes lenticular shape bleed
Dura Matter inner layer
Tentorium or tent like structure (the shelf)
- separates upper brain from lower brain
- Tentorium Incisure - hole where upper/lower brain (uncus) meets in middle.
Two classifications of Head injuries
- Supratentorial (above) herniation attempting to force upper brain through incisure. Descending herniation. Most common.
- Uncal Herniation: brain attempting to shift down through Tentorium incisure. - Infratentorial Herniation.
Epidural space versus subdural space
Epidural space- potential space between the skull and the dura
Subdural Space - potential space between the dura and the arachnoid membrane
Monitoring ICP - transducer needs to be even w/
Must be even w/ foramen of Munro (Little tube connects the lateral ventricles with the third ventricle then through the aqueduct of Silvius to the fourth ventricle)
-level with ear canal or bony prominence behind ear
Cerebral Perfusion Pressure Calculation
CPP = MAP - ICP
- normal ICP 0-10 mmHg
- goal CPP : >60 mmHg
MAP calculation
MAP = (SBP + 2(DBP)) / 3
Or
MAP = DBP + 1/3(Pulse Pressure)
Pulse Pressure = SBP - DBP
Decorticate posturing indicates:
Damage above the cerebellum & brainstem
-supratentorial
Decerebrate indicates:
Damage to brainstem. Or compression of the thalamus and brain stem.
Causes of signs in cushings triad
HTN: increased systolic pressure w/ decrease vascular compliance
- defensive mechanism
Bradycardia: pressure on vagus nerve (theorized)
Respiratory changes: blue wire has been cut, not compensatory.
Positioning head injury
Eyes forward (natural inline position)
- allows venous drainage of brain.
- blood drainage from one part of the brain allows drainage from parts that do not easily drain.
- head turned to R is worse than to the L
HOB 15-30%
-gravity helps evacuate head.
Other treatment for head injuries
Limit noxious stimulus -suctioning, invasive procedures noise - ear plugs even in coma state Limit atmospheric changes Keep patient tanked up - dry head injury will not survive Normothermia Normal electrolytes
Sedation for head injury patients
Propofol is best as it wears off quickly
Benzos take longer to wear off.
What happens with hypoventilation and head injury patients?
Cerebral steal or luxury perfusion
- vasodilation due to increased co2
- non-injured areas of brain vasodilate and rob essential blood from injured site.
What happens with hyperventilation and head injury patients?
Reverse steal or Robin Hood Effect
- Rob from rich and give to the poor
- blood vessels leading to injured brain relax and open in attempt to perfuse. Non-injured brain is vasoconstricted to an unhealthy level in attempt to push blood to injured area.
Hypertonic solutions to use
Mannitol or hypertonic saline
- assure adequate resuscitation first
- foley Cath must be in place
- ideally, CVP pressure should guide use of these drugs.
Barbiturate coma
Decreases O2 demand
- minimizes brain function
- requires neurologist decision
- complications exist
- thiopental too short acting
- Phenobarbital drug of choice
Skull to brain
Skull => epidural space => Dura matter (outermost Layer) => Tentorium Dura matter (inner layer) => sub dural space => arachnoid membrane => subarachnoid space => Pia matter => brain
