L12 - Arousal, Coma & Unconsciousness - Implications for Management of Head Trauma Flashcards
List 2 important characteristics of consciousness.
Which areas of the brain are responsible for these characteristics?
1 - Arousal (cortical areas of the brain)
- This is the level of consciousness
2 - Awareness (subcortical areas of the brain)
- This is the content of consciousness
What 4 structures of the CNS are involved in the maintenance of consciousness?
1 - Ascending reticular activating system
2 - Thalamus
3 - Striatum
4 - Globus pallidus interna
Which structures constitute the ascending reticular activating system?
- Pedunculopontine nucleus
- Hypothalamus
- Basal forebrain
Describe the mesocircuit model of consciousness.
During consciousness:
- The pedunculopontine nucleus excites the central thalamus
- The thalamus excites, and is excited by, the areas of the cortex necessary for consciousness
To allow consciousness to continue:
- The globus pallidus interna, when uninhibited, inhibits the thalamus and pedunculopontine nucleus, causing unconsciousness
- Therefore, during consciousness, the globus pallidus interna must be inhibited by the striatum
- The striatum is active during consciousness due to the excitatory innervation it receives from the thalamus and frontal cortex
During unconsciousness:
- The activity of the thalamus decreases, reducing excitation of the striatum from the thalamus and frontal cortex
- This results in greater inhibition of the thalamus and pedunculopontine nucleus from the globus pallidus interna
What are the neurotransmitters used by the ascending reticular activating system?
- Orexin
- Adrenergic
- Cholinergic
What is brainstem death?
- Irreversible loss of brainstem function
- Permanent loss of potential for consciousness & capacity to breathe
What is a coma?
A state in which there is a complete failure of arousal, with:
1 - No spontaneous eye opening
2 - Inability to be awakened by application of vigorous sensory stimulation
What is a vegetative state / unresponsive wakefulness?
- A complete absence of behavioural evidence for self or environmental awareness
- Preserved capacity for spontaneous or stimulus-induced arousal evidenced by sleep-wake cycles
What is a minimally conscious state?
- A state in which cognitively-mediated behaviour occurs, however inconsistently
- The behaviour is reproducible
- The behaviour can be sufficiently purposeful and sustained long enough to be differentiated from a reflex
How is emergence from a minimally conscious state defined?
1 - Functional communication (e.g. accurate yes / no responses)
2 - Functional object use (e.g. bringing a pencil to a sheet of paper)
What is akinetic mutism?
- A subtype of minimally conscious state in which the reduction in goal-directed behaviour is due to a severely diminished drive rather than diminished arousal
- Patients with akinetic mutism therefore respond to high-intensity sensory stimuli, as their sensory systems are affected to a lesser degree than patients in a minimally conscious state
What are the characteristics of a post-traumatic confusional state (delirium)?
1 - Prolonged periods of consciousness
2 - Disorientation
3 - Functional object use
4 - Functional communication
5 - Cognitive impairments
What is locked-in syndrome?
- A de-efferented state characterised by quadriplegia and paralysis of the lower cranial nerves
- Patients with locked-in syndrome retain consciousness and can communicate by vertical eye movements and blinking
What are the subclasses of locked-in syndrome?
1 - Classical locked-in syndrome
- Upgaze and blinking with anarthria, tetraparesis and preserved consciousness
2 - Incomplete locked-in syndrome
- As above, but some movement in the limbs
3 - Complete locked-in syndrome
- No limb or eye movements, but preserved consciousness
Which actions are tested in the Glasgow coma scale?
- Eye opening
- Best verbal response
- Best motor response
How is the Glasgow coma scale scored?
- Each of the components are graded - max score of 15 & min score of 3
- GCS <9 defined as coma (GCS = 3-8)
What is considered a significant change in the Glasgow coma scale?
A change of 2 points is significant
List 5 pupil signs of brain damage.
What do these signs indicate?
- Diencephalic – small reactive
- Pretectal – large fixed pupils
- Pons – pinpoint
- Midbrain – midposition, fixed
- Uncal herniation – unilateral dilation
Which drug classes cause pinpoint pupils?
- Opiates
- Anticholinesterases
What causes fixed dilated pupils?
- Hypoxic encephalopathy
- Anticholinergics
- Botulism
What is hemiplegia?
Paralysis on one side of the body
What are decorticate and decerebrate posturing?
- Decorticate – elbows, wrists & fingers flexed, & legs extended & rotated medially
- Decerebrate – hyperextension & hyperpronation; neck extension
What is the equation for cerebral perfusion pressure?
What is the critical cerebral perfusion pressure?
- Normal ICP <10 mmHg
- CPP = MAP – ICP: increased ICP begins to impede cerebral flow -> critical when CPP <60 mmHg
What is Cushing’s triad?
- HTN
- Bradycardia
- Resp irregularity
What breathing patterns are caused by brain injury?
- Forebrain – increased sensitivity to CO2 -> regular waxing & waning of resp
- Midbrain – hyperventilation
- Pons – apneustic prolonged inspiration
- Medulla – slow, shallow respiration
What are the pitfalls in ABI consciousness assessment?
- Drugs
- Epilepsia partialis continuans
- Critical illness neuromyopathy
- Late hydrocephalus
- Pituitary failure
- Type 2 resp failure w/ CO2 narcosis
- Hypothermia
- Occult spinal injury
