Disorders of consciousness

Question 1

What are the main disorders of consciousness and how can they be distinguished?

Answer 1

Consciousness has two main components: wakefulness and awareness

Coma: (absent wakefulness and absent awareness)

• lasting >6 hours
• cannot be woken
• doesn’t respond to painful stimuli
• lacks normal sleep-wake cycle
• does not initiate voluntary actions

Vegetative state: (wakefulness but absent awareness)

• severe cortical damage with preservation of brainstem function
• preserved capacity for external stimulus to influence arousal: retain sleep-wake cycle, range of spontaneous behaviours
• absence of environmental awareness or awareness of self

Minimally conscious state: (wakeful and minimal awareness)

• severely altered consciousness in which some evidence of environmental or self awareness exists
• • must have reproducible responses which are not solely reflex arc movements.

Locked-in syndrome: (preserved wakefulness and awareness, BUT paralysis)

These states are not necessarily fixed.

Question 2

What are the causes of disordered consciousness?

Answer 2

1. Traumatic
   - axonal injury
   - bleed
   - vasospasm
2. Vascular
   - stroke (basilar infarct)
   - SAH
3. Infective
   - encephalitis
   - abscess
   - sepsis
4. Metabolic
   - hypo/hyperglycaemia
   - hyponatraemia
   - hepatic encephalopathy
   - uremic encephalopathy
   - hypothermia
5. Hypoxia
   - cardiac arrest
   - respiratory failure
   - drowning
6. Drugs
   - anaesthetic agents
   - benzodiazepines
   - alcohol

Question 3

How can you prognosticate after disordered consciousness and brain injury?
What factors indicate a potentially favourable prognosis?

Answer 3

ERC and ESICM recommend that multiple predictors should be used to prognosticate and that prognostication should take place after a period of 72 hours of stability and optimisation.

Days 1-2:

• Controlled temperature 32-36 for at least 24hrs (avoidance of pyrexia for 72hrs)
• rewarming

After 72hrs:

• check motor score of GCS
• M<4 plus:
• at least 2 of:
  
  • absent pupil or corneal reflexes
  • bilaterally absent N20 SSEPs
  • highly malignant EEG (burst suppression, unreactive, status)
  • elevate NSE
  • status myoclonus <72h
  • anoxic injury on CT/MRI

…indicates poor prognosis

A potentially favourable prognosis:

• young age
• traumatic aetiology
• short duration of impaired consciousness