Arousal, Coma and Unconsciousness - Implications for Management of Head Trauma Flashcards
(43 cards)
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.
List 4 structures of the CNS that are involved in the maintenance of consciousness.
1 - Ascending reticular activating system.
2 - Thalamus.
3 - Striatum.
4 - Globus pallidus interna.
List the structures that constitute the ascending reticular activating system.
1 - Pedunculopontine nucleus.
2 - Basal forebrain.
3 - Hypothalamus.
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.
List the neurotransmitters used by the ascending reticular activating system.
1 - ACh.
2 - Various amines, such as adrenergic neurotransmitters.
Which area of the brain is responsible for processing of interoception?
The anterior cingulate gyrus.
Which area of the brain is responsible for processing of exteroception?
The parietal lobes.
List the diagnostic criteria for brainstem death.
1 - Demonstration of coma.
2 - Absence of brainstem reflexes.
3 - Absence of motor responses.
4 - Apnoea test, including delivery of 100% oxygen without ventilation. This should result in high oxygen saturation but also rising CO2 in a patient with brainstem death.
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 / unaware wakefulness?
A complete absence of behavioural evidence for self or environmental awareness.
Give an example of evidence that patients in a vegetative state / unaware wakefulness that there is preserved capacity for some stimulus-induced arousal.
- Patients in a vegetative state still have functional sleep-wake cycles.
- This indicates that there is preserved capacity for some stimulus-induced arousal.
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 follows a minimally conscious state?
A post-traumatic confusional state (delirium).
List 5 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.
List 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.
Describe the progression of states of consciousness following a brain injury.
1 - Acute brain injury causes a coma.
2 - A coma is followed by death, locked-in syndrome or a vegetative state.
3 - A vegetative state is followed by a minimally conscious state or persistence of the vegetative state.
4 - A minimally conscious state is followed by emergence.
List the states of consciousness.
List the relative levels of arousal and awareness for each.
1 - A coma involves no arousal and no awareness.
2 - A vegetative state involves full arousal but no awareness.
3 - A minimally responsive state involves full arousal but only some awareness.
4 - Locked-in syndrome involved full arousal and full awareness.
What type of hernia might result from an extradural haematoma?
What type of hernia might result from a posterior fossa-expanding lesion?
- An extradural haematoma might result in a lateral tentorial herniation, in which there is herniation of the medial temporal lobe through the tentorial notch.
- A posterior fossa-expanding lesion might result in a tonsillar herniation, in which there is herniation of the cerebellar tonsils through the foramen magnum.
If fluid leaks into the intracranial space or the brain swells, which other volumes decrease to compensate and keep the intracranial volume constant?
What is this theory known as?
- Interstitial fluid and cerebrospinal fluid decrease to keep intracranial volume constant.
- This is known as the Monro-Kellie hypothesis.
What is the critical intracranial volume?
The point at which the interstitial fluid and cerebrospinal fluid can no longer decrease to compensate for an increase in intracranial volume, so the intracranial pressure begins to increase rapidly.
What is coning?
When does it occur?
- Herniation of the brain.
- It occurs when intracranial pressure becomes too high.
