Consciousness Flashcards
consciousness
an active process often defined as awareness of the self and the environment
2 components:
arousal (wakefulness)
awareness (content)
arousal (wakefulness)
level of alertness
result of information arising from the reticular activating system
Other structures included: rostral pontine, mesencephalic tegmentum, midline, and intralaminar thalamic nuclei
awareness (content)
requires an intact cerebral cortex and its connections to other subcortical structures
cognition
- involves attention, sensation/perception, explicit memory, executive function and motivation
- depends on cerebral cortical activity
physiological vs. pathological unconsciousness
sleep is reversible with stimulation
pathological unconsciousness is due to structural or functional disturbances
ascending reticular activating system (ARAS)
- rostral brainstem tegmentum and diencephalon and associated cortical projections.
- signals related to level of arousal and awareness pass through the ARAS, are carried to the two thalami bilaterally, and then ascend to the rest of the cortex.
- signals are important for sleep- wake transitions and attention.
somnolence
drowsiness/near-sleep
lethargy
extreme fatigue or drowsiness
obtundation
mild to moderate reduction in alertness, w/ a lesser interest in environment
stupor
condition of deep sleep or similar behavioral unresponsiveness from which subject can be aroused only w/ vigorous and continuous stimulation
responds to VOICE, PAIN
-like obtundation, but to a greater degree
coma
- unresponsive, sleep-like (but no cycles) state lacking arousal/awareness for 1+ hour
- movements=pathologic or do not exist
- eyes do not open
encephalopathy
- syndrome of global brain dysfunction
- states of altered consciousness caused by damage or suppression of the ARAS or of both cerebral hemispheres
Persistent Vegetative State:
+30days of complete unawareness with no localizing motor activity, no ability to follow commands (cortex NOT functioning)
- intact circulatory, brainstem, and respiratory function, normal sleep-wake cycles
- may spontaneously open eyes to stimuli but without recognition.
- often follows a pd of coma
Non-traumatic vegatative state 1+ month = _____ chance of recovery beyond severe disability.
Non-traumatic vegatative state 1+ month = NO chance of recovery beyond severe disability.
Traumatic state 1-6 months = _____ chance of recovery of good-moderate disability.
Traumatic state 1-6 months = 25% chance of recovery of good-moderate disability.
Minimally Conscious State (MCS)
- between PVS and normal consciousness
- can follow simple commands (yes/no responses via gestures or verbally)
- intelligible verbalization
- purposeful behavior (rather than reflexive)
which type of coma presents w/ NO eye movements
subcortical coma
brainstem is working but cortex is not –> which disturbance of consciousness?
persistent vegetative state
After TBI, MCS or PVS has a greater recovery?
MCS
locked-in syndrome
state of selective “de-efferentation” of all 4 extremities and lower CN
- pt is awake, can hear
- NO movement and speech
- vertical eye movements/blinking possible (oculomotor spared)
- ventral pontine lesion
possible sites of lesions that compress the ARAS (compressive, cause coma)
cerebral: bilateral subdural hematomas
diencephalon: thalamus (hemorrhage), hypothalamus (tumor)
brainstem: uncal herniation, cerebellum
possible sites of lesions that directly damage the ARAS (destructive)
cortex (acute anoxia)
subcortical (delayed anoxia)
diencephalon (thalamus infarct)
brainstem (midbrain, pons stroke)
multifocal and diffuse disease that may also lead to coma
- Ischemia or hypoxia
- glucose disorders
- organ system diseases
- intoxication
- ionic or acid/base imbalances
- thermoregulation disorders -infections
- cerebral vasculitis
- other (prion…)
how does intracranial HTN lead to altered consciousness?
elevated ICP –> decreases global cerebral blood flow –> compartmental changes in pressure –> herniation syndromes –> anatomical distortion of adjacent structures OR compression of vasculature causing infarcts
vestibulo-ocular reflex (Doll’s Eyes)
afferent/efferent limbs
- tests VIII, VI, III
- normally, when head turned, eyes move in opp dir
- overcome in awake pt
afferent: semicircular canals –> CN VIII
efferent: abducens and oculomotor nuclei to respective contralateral and ipsilateral EOMs
caloric reflex testing
- surrogate for doll’s eyes maneuver, performed w/ severe brainstem injuries
- cold water is irrigated into the external auditory canal, sensed by semicircular canals
- NOT performed in awake pt (vertigo + vomiting)
cold water in L ear to test caloric reflex, what happens?
cold water in L ear –> endolymph falls –> convective current (circular movement of endolymph, same thing that happens as if moving head away from stimulus)
decreases rate of CN VIII firing on that side –> eyes turn toward IPSILATERAL ear
if awake to correct –> fast-paced nystagmus back to midline (twd CONTRALATERAL ear)
Glasgow Coma Score
objective score with three categories
- eye opening
- verbal response
- motor response
best score: fifteen
worst score: three (comatose, completely unresponsive)
severe brain injury <8-9
moderate with 8 or 9-12
minor with greater or equal to 13
FOUR score
Full Outline of UnResponsiveness
- incorporates respiration and brainstem reflexes in generating Glasgow Coma score
1) eye response
2) motor response
3) brainstem reflexes
4) respiration
HTN and Bradycardia set off warning bells for…
INTRACRANIAL HTN
brain death
- total cessation of all brain and brainstem function with a known, irreversible, demonstrable cause
- NO drug intoxication, no severe overlying condition, no hypothermia
- Failed apnea test (absence of respiration with PaCO2 > 60mmHg)
- Absent reflexes, absent response to pain
confirmatory tests for brain death
EEG (electro cerebralsilence)
Angiography (no filling at level of circle of Willis)
Nuclear flow study (SPECT. No isotope uptake in brain)
Transcranial Doppler (no blood flow)
not necessary to do; only if severe facial trauma, drug intoxication, severe metabolic disturbances, apnea test cannot be performed safely
non-brain death causes of fixed pupils
- Anti-cholinergic drugs
- Tri-cyclic antidepressants
- Neuromuscular blocking agents
- Pre-existing eye disease
non-brain death causes of lack of vestibulocular reflexes
Ototoxic agents
Vestibular suppression
Pre-existing disease
Basilar skull fracture
non-brain death causes of lack of no motor activity
- Neuromuscular blocking agents
- Locked in state
- Sedative drugs
non-brain death causes of lack of isoelectric EEG
Sedative drugs Anoxia Hypothermia Encephalitis Trauma
poor prognosis signs in post-anoxic coma:
- absent pupillary responses, day ___
- absent corneal responses, day ___
- absent motor responses, day ___
- absent somatosensory evoked potentials in week ___
poor prognosis signs in post-anoxic coma:
- absent pupillary responses, DAY 1
- absent corneal responses, DAY 1
- absent motor responses, DAY 3
- absent somatosensory evoked potentials in WEEK 1
brain death cardinal features
- unresponsive, comatose
- no brainstem reflexes (pupillary light, corneal, vestibuloocular, gag, cough)
- apnea test
