Coma & hypoxic brain injury

Written by Louise Milburn and Jen Rogers

4th year medical students

(with occasional editorial input from me)

Have you listened to the lecture on coma and consciousness? If not, click here

Assessment

Assessing a patient’s consciousness level is important in monitoring changes in their condition and prognosticating. Here we will discuss how to assess someone who is in an impaired state of consciousness.

It is useful to consider some definitions:

Coma: absence of wakefulness and awareness

The person is unrousable and unresponsive for a period of more than six hours. They cannot be awakened, they do not have a normal sleep-wake cycle, they do not initiate voluntary actions and they do not respond normally to light, sound or pain.

Vegetative state: wakefulness with absent awareness

The person is awake, they have a sleep-wake cycle, they initiate some reflexive and spontaneous behaviours and they can be aroused either spontaneously or by stimulus.

Minimally conscious state: wakefulness with minimal awareness

The person’s consciousness is severely altered but there is evidence of self-awareness or environmental awareness. The person’s responses can be inconsistent but reproducible.

Locked-in syndrome: wakefulness and awareness but without voluntary movement.

The person can often communicate using movements of the eyes or eyelids.

Brainstem death

The person has lost all brainstem functions and has no spontaneous respiratory effort.

In 2013, the Royal College of Physicians produced a guideline on ‘prolonged disorders of consciousness’, which usefully lists the criteria for the above states of consciousness.

If they aren’t responding, is there another reason? Think outside the box.

  • Hearing impairment
  • Tracheostomy tube inhibiting speech and/or sense of smell
  • Language barrier
  • Sedation
  • Position compromising visual field and range of movement
  • Anaesthetic agents and neuromuscular blocking drugs

Remember that assessment of a patient with impaired consciousness is not a one-off: it needs to be done regularly and consistently. Make sure you monitor the patient for a

A scoring system is a useful way of assessing consciousness levels:

FOUR score

The Full Outline of UnResponsiveness Score (FOUR Score) is a grading scale that allows medical professionals to determine the extent of a patient’s level of consciousness.

Four areas are assessed, with each area having possible scores from 0-4:

Eye response 4 Eyelids open, tracking or blinking on command
3 Eyelids open, not tracking
2 Eyelids closed, open to loud voice
1 Eyelids closed, open to pain
0 Eyelids closed, closed with pain
Motor response 4 Thumbs up, make a fist or make ‘peace’ sign
3 Localises to pain
2 Flexes to pain
1 Extends to pain
0 No response, or generalised myoclonic status
Brainstem reflexes 4 Normal pupil and corneal reflexes
3 One pupil wide and fixed
2 Pupil or corneal reflexes absent
1 Pupil and corneal reflexes absent
0 Absent pupil, corneal and cough reflexes
Respiration 4 Not intubated, normal breathing
3 Not intubated, Cheyne-Stokes breathing
2 Not intubated, irregular breathing
1 Breaths above ventilator rate
0 Apnoea or breaths at ventilator rate

 

A full guide to using the FOUR Score can be found here.

Why FOUR Score and not the Glasgow Coma Scale (GCS)?

Due to the verbal component of the test, the GCS cannot reliably be used in patients with endotracheal tubes. It is; however, important to note that GCS is still regularly used in assessing patients in a minimally conscious state.

Sensory Modality Assessment and Rehabilitation Technique (SMART)

SMART assessments last for ten sessions at different times over different days, and consist of looking at the patient’s behaviour both at rest and in response to stimuli. The patient’s behaviour is monitored for ten minutes in an unstimulating environment, then an assessment of response to stimuli is made.

All five senses are assessed using a five-point system

  1. No response
  2. Reflex response
  3. Withdrawal response
  4. Localising response
  5. Differentiating response

Once the SMART assessment has been carried out, an appropriate treatment regimen is designed using the results.

JFK Coma Recovery Scale – Revised (CRS-R)

The CRS-R is an in-depth chart designed to monitor recovery from a coma over time, in a similar way to the EWS. It uses six categories with varying scores per category:

  • Auditory function scale
  • Visual function scale
  • Motor function scale
  • Oromotor/verbal function scale
  • Communication scale
  • Arousal scale

There is also a section dedicated to brainstem reflexes over time. It measures:

  • Pupillary
  • Corneal
  • Spontaneous eye movements
  • Oculocephalic reflex (Doll’s eyes)
  • Postural responses

There are strict protocols to use when following the CRS-R, details of which are included in the documentation, included in part to provide consistency even if the examiner changes. These protocols include commands, such as, “Look away from me”, and, “Look up”.

Electroencephalogram (EEG)

The EEG is used both to guide prognosis and to assess the patient’s level of consciousness. There have been several attempts to set up systems to classify the EEG in coma, but none are totally reliable, as there are may potential confounding factors in their interpretation.

Prognostic factors:

Predictors of poor prognosis

The brain stem is more resistant to anoxic–ischemic damage than the cerebral cortex; thus, compromise of brain-stem reflexes suggests that the cortex must be severely damaged. However, preserved brain-stem reflexes do not imply intact   cortical function. Assessing the cortical function of patients can be very difficult so repeated observation and testing is recommended.

An absence of pupillary reflexes is most sensitive at 72hrs. Patients who have no pupillary response at 72hrs generally have poor outcomes. Similarly an absent corneal reflex at 72hrs suggests a poor outcome, usually death or significant neurological disability.

If patients have no motor response or extension to pain at 72 hours (i.e. worse than flexion) this can be helpful, but can be confounded by therapeutic hypothermia in some cases. Myoclonic status epilepticus (MSE) must be differentiated from other forms of seizure which can be seen to be used prognostically but can be very sensitive.

Bilateral absence of cortical Somatosensory Evoked Potentials SSEPs (especially measuring primary somatosensory cortex N2O response) within 1 to 3 days can also be useful. Serum neuron-specific enolase is a chemical released by the brain during hypoxia is often significantly higher in patients with poor outcomes 1 to 3 days after injury.

Other measures can be less useful, such as CPR for greater than 8 minutes, or it taking more than 30mins for return of spontaneous circulation to return. Although these patients may have poor outcomes they are not accurate at predicting a poor outcome. Similarly an anoxic coma lasting more than 72 hours is not accurate. Burst suppression or generalized epileptiform discharges on EEG are usually signs of poor outcomes but not always. Given that critical decisions regarding continuing care are made on the basis of prognostic predictors it is important that those used to predict poor outcomes are robust, and the American Association of Neurologists has deemed that the above measures do not have a high enough sensitivity, meaning some patients may be labeled as having a poor prognosis who could go on to make a meaningful recovery (Wijdicks et al).

Predictors of better prognosis that can be useful include:

  • recovery of brainstem reflexes within 48hours
  • hypothermia at the time of arrest (i.e. immersion)
  • young age
  • primary pulmonary event leading to hypoxaemia

 

References:

Berek K, Lechleitner P, Luef G, et al. Early determination of neurological outcome after prehospital cardiac arrest. Stroke 1995;26:543-9

GivenGain. FOUR Score Instruction Guide. link.

Howard RS, Holmes PA, Koutromanidis MA. Hypoxic-ischaemic brain injury. Practical Neurology. 2011;11:1 4-18.

Johnson Rehabilitation Institution. Coma recovery scale – revised. link

Royal College of Physicians. Prolonged disorders of consciousness. National clinical guidelines. 2013. link

University of Cambridge. Clinical assessment procedure. link

Wijdicks EFM, Bamler WR, et al. Validation of a new coma scale: The FOUR score. Annals of Neurology. 2005;58:585-593.

Young GB. Neurological prognosis after cardiac arrest. N Engl J Med2009;361:605-11.

Zandbergen EG, Hijdra A, Koelman JH, et al. Prediction of poor outcome within the first 3 days of postanoxic coma. Neurology 2006;66:62-8.

 

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