Arousal, Coma and Unconsciousness - Implications for Management of Head Trauma

Question 1

List 2 important characteristics of consciousness.

Which areas of the brain are responsible for these characteristics?

Answer 1

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.

Question 2

List 4 structures of the CNS that are involved in the maintenance of consciousness.

Answer 2

1 - Ascending reticular activating system.

2 - Thalamus.

3 - Striatum.

4 - Globus pallidus interna.

Question 3

List the structures that constitute the ascending reticular activating system.

Answer 3

1 - Pedunculopontine nucleus.

2 - Basal forebrain.

3 - Hypothalamus.

Question 4

Describe the mesocircuit model of consciousness.

Answer 4

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.

Question 5

List the neurotransmitters used by the ascending reticular activating system.

Answer 5

1 - ACh.

2 - Various amines, such as adrenergic neurotransmitters.

Question 6

Which area of the brain is responsible for processing of interoception?

Answer 6

The anterior cingulate gyrus.

Question 7

Which area of the brain is responsible for processing of exteroception?

Answer 7

The parietal lobes.

Question 8

List the diagnostic criteria for brainstem death.

Answer 8

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.

Question 9

What is a coma?

Answer 9

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.

Question 10

What is a vegetative state / unaware wakefulness?

Answer 10

A complete absence of behavioural evidence for self or environmental awareness.

Question 11

Give an example of evidence that patients in a vegetative state / unaware wakefulness that there is preserved capacity for some stimulus-induced arousal.

Answer 11

• Patients in a vegetative state still have functional sleep-wake cycles.
• This indicates that there is preserved capacity for some stimulus-induced arousal.

Question 12

What is a minimally conscious state?

Answer 12

• 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.

Question 13

How is emergence from a minimally conscious state defined?

Answer 13

1 - Functional communication (e.g. accurate yes / no responses).

2 - Functional object use (e.g. bringing a pencil to a sheet of paper).

Question 14

What is akinetic mutism?

Answer 14

• 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.

Question 15

What follows a minimally conscious state?

Answer 15

A post-traumatic confusional state (delirium).

Question 16

List 5 characteristics of a post-traumatic confusional state (delirium).

Answer 16

1 - Prolonged periods of consciousness.

2 - Disorientation.

3 - Functional object use.

4 - Functional communication.

5 - Cognitive impairments.

Question 17

What is locked-in syndrome?

Answer 17

• 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.

Question 18

List the subclasses of locked-in syndrome.

Answer 18

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.

Question 19

Describe the progression of states of consciousness following a brain injury.

Answer 19

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.

Question 20

List the states of consciousness.

List the relative levels of arousal and awareness for each.

Answer 20

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.

Question 21

What type of hernia might result from an extradural haematoma?

What type of hernia might result from a posterior fossa-expanding lesion?

Answer 21

• 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.

Question 22

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?

Answer 22

• Interstitial fluid and cerebrospinal fluid decrease to keep intracranial volume constant.
• This is known as the Monro-Kellie hypothesis.

Question 23

What is the critical intracranial volume?

Answer 23

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.

Question 24

What is coning?

When does it occur?

Answer 24

• Herniation of the brain.

- It occurs when intracranial pressure becomes too high.

Question 25

How is high intracranial pressure treated?

Answer 25

With a craniotomy.

Question 26

List the actions tested in the Glasgow coma scale.

Answer 26

1 - Eye opening.

2 - Verbal response.

3 - Best motor response.

Question 27

How is the Glasgow coma scale scored?

Answer 27

• Each action is scored:

1 - Eye opening is scored from 4 - not testable.

2 - Verbal response is scored from 5 - not testable.

3 - Best motor response is scored from 6 - not testable.

• A total score is given out of 15.

Question 28

What is considered a significant change in the Glasgow coma scale?

Answer 28

A change of 2 points is considered a significant change.

Question 29

List 5 pupil signs of brain damage.

What do these signs indicate?

Answer 29

1 - Small reactive pupils indicate diencephalic injury.

2 - Fixed dilated pupils indicate pretectal damage.

3 - Pinpoint pupils that remain small in bright light indicate pons damage.

4 - Fixed midposition pupils indicate midbrain damage.

5 - A unilateral fixed dilated pupil indicates uncal herniation.

Question 30

List 2 drugs that cause pinpoint pupils.

Answer 30

1 - Opiates.

2 - Anticholinesterases.

Question 31

List 2 conditions that cause fixed dilated pupils.

Answer 31

1 - Hypoxic encephalopathy.

2 - Botulism.

Question 32

Define hemiplegia.

Answer 32

Weakness, spasticity and loss of control in one half of the body.

Question 33

Define decorticate posturing.

Define decerebrate posturing.

Answer 33

• Decorticate posturing is abnormal posturing due to damage to the cortex.
• Decerebrate posturing is abnormal posturing due to damage to the brainstem.

Question 34

What is the average range of intracranial pressure?

Answer 34

7-15 mmHg.

Question 35

What is the equation for cerebral perfusion pressure?

Answer 35

Cerebral perfusion pressure = mean arterial pressure - intracranial pressure.

Question 36

What is the critical cerebral perfusion pressure?

What happens at this point?

Answer 36

• 60 mmHg.

- It is the point where perfusion is sufficiently low as to cause hypoxic injury.

Question 37

What is Cushing’s triad?

Answer 37

A triad of signs of raised intracranial pressure:

1 - Hypertension.

2 - Bradycardia.

3 - Respiratory irregularity.

Question 38

List 4 breathing patterns caused by brain injury.

Answer 38

1 - Cheyne-Stokes (waning of respiration).

• Caused by forebrain injury.

2 - Hyperventilation.

• Caused by midbrain injury.

3 - Apneustic prolonged inspiration (deep, gasping inspiration with a pause at full inspiration followed by a brief, insufficient release).

• Caused by pons injury.

4 - Bradypnoea and shallow respiration.

• Caused by specific nuclei dysfunction, namely CN 9, 10 and 11 (those involved in the respiratory centres).

Question 39

Define brainstem death.

Answer 39

A state in which a person no longer has any brainstem functions and has permanently lost the potential for consciousness and the capacity to breathe.

Question 40

How often are spinal reflexes seen in patients with brainstem death?

Answer 40

Spinal reflexes are seen in 75% of patients with brainstem death.

Question 41

What is the Lazarus sign?

Answer 41

A reflex in which patients with brainstem death briefly raise their arms and then drop them crossed on their chests.

Question 42

List 3 scales used to assess consciousness state.

Answer 42

1 - Coma recovery scale.

2 - Sensory motor rehabilitation technique (SMART).

3 - Wessex head injury matrix (WHIM).

Question 43

Give an example of a pitfall in consciousness assessments.

Answer 43

• Some septic patients develop dysfunction of muscles and peripheral nerves, known as critical illness neuromyopathy.
• This is a completely recoverable form of plegia that can mask normal upper motoneurone function.