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Gyrus Think: Persistent Disorder of Consciousness what is it? and the challenges of determining life expectancy.

Karthik Ajith and Doug McCorry

23 April 2024   |   Gyrus Group

1. Definition and Types of Persistent Disorder of Consciousness

Consciousness is a subjective, first-person phenomenon and is hence difficult to measure.1 Although there are no simple clinical signs or lab tests to evaluate consciousness, in clinical settings, it is often deduced from observing a range of behaviours as part of a neurological examination.2 Two key components of this evaluation are wakefulness and awareness.2

Wakefulness refers to a state in which the eyes are open and there is a degree of motor arousal evidenced by basic reflexes like coughing, swallowing, and sucking. 2,3

Awareness refers to the ability to have conscious experiences of any kind.2 It involves more complex thought processes than wakefulness and hence is more difficult to assess.3

The main disorders of consciousness are given in Table 1.

Disorder Wakefulness Awareness
Coma Absent Absent
Vegetative State (VS) Present Absent
Minimally Conscious State (MCS) Present Minimally Present

Clinically determining the category in which a particular patient falls is often a tricky problem and studies have shown that misdiagnosis, especially misdiagnosing MCS as VS, is very prevalent.4-6 MCS is often confused to be VS when the patient has a motor or visual impairment that prevents them from following commands or if the clinician omits to pick up their visual pursuit as a sign of awareness.7 Clinicians have devised several ways to help make this distinction, such as using behavioural assessment tests that provide a structured guide to assess responses to stimuli, (eg- Coma Response Scale-Revised), and using advanced tests, such as EMG, EEG, PCI, and fMRI that can detect evidence of consciousness without relying on outward responses.7

Since Persistent Disorder of Consciousness (PDOC) can happen due to so many causes, it is difficult to find reliable statistics on their numbers, but according to estimates, patients with PDOC admitted to neurorehabilitation facilities in England range from 365 to 1,750 each year.8,9,10 Of PDOC patients in nursing homes in England and Wales, approximately 4000 to 16,000 of are in VS, and around three times as many are in MCS.10 Using crowdsourcing methods, the annual incidence of coma in the UK was found to be 135 per 100,000.11

Any disorder of consciousness that lasts for longer than 4 weeks after a sudden onset brain injury is termed a Prolonged Disorder of Consciousness.2 Current consensus suggests that Prolonged Disorders of Consciousness form a continuous spectrum of awareness and additionally, for some patients, the level of consciousness may fluctuate with time.2 Hence, these disorders cannot be easily divided into water-tight compartments as given in Table 1.2

2. Causes of PDOC

Common causes of PDOC are given in Table 2.

Causes Examples
Trauma Head trauma after a road traffic accident
Vascular Event A brain hemorrhage or stroke
Hypoperfusion (reduced blood supply to the brain) A cardiac arrest or severe blood loss
Infection or Inflammation Infections like meningitis and encephalitis. Inflammatory disorders like vasculitis.
Toxic or Metabolic Drug or alcohol poisoning.
Severe hypoglycemia.

Traumatic Brain Injury (TBI) is a common cause of PDOC, and loss of consciousness is more prevalent in severe TBI.12 From 2014 to 2015, there were 15,822 TBI patients referred to neurosurgical centres within the UK, and although most of them had a mild TBI (65%), a significant number (25%) had severe TBIs as well.13

Irrespective of the cause, the care for a patient with PDOC is challenging right from the acute setting in the hospital to long-term care, requiring intensive rehabilitation and nursing. The Royal College of Physicians National Guidelines on PDOC following sudden onset brain injury forms an extensive resource and reference for this complex management.2

3. Life Expectancy in Traumatic Brain Injury

Life expectancy refers to the average number of years lived by a given member of a group of individuals, which in this case are patients suffering from TBI.14 An accurate estimate of life expectancy helps in long-term care planning and hence it is of vital importance to patients, caregivers, clinicians, and understanding the costs of care in legal claims.15

Several studies have shown that the life expectancy of TBI patients is lower than those without TBI in the population.15 In cases where death happens a short while after TBI, the most common cause is damage to the brain itself, especially from injury to the brain stem, brain oedema, and brain compression.14 Besides this, chest infections also cause significant mortality in the short term.14 In the patients who manage to survive longer the reasons for why survival is reduced may be complex: is it the effects of the brain injury [causal], or factors associated with why a brain injury occurred in the first place. Causally related factors why life expectancy would be reduced include diseases of the circulatory system (such as heart attacks and pulmonary embolisms), infections of the respiratory tract (such as pneumonia), post-traumatic epilepsy, and suicide. 14,16

Factors related to Life Expectancy in TBI

Medical experts are often asked to provide estimates of life expectancy for patients with PDOC due to TBI, but this remains a very challenging area to provide guidance on.14 Several factors alter the life expectancy in such cases and they are briefly discussed below.

In the short term, brain injury severity factors such as level of consciousness after the injury (Glasgow Coma Scale) and duration of post-traumatic amnesia are good predictors of survival.14 In the long term, of the several factors discussed below, the most important ones are the age of the patient and the severity of disability, especially the degree of mobility regained after the injury.14,15 A brain injury is generally considered a non-progressive process and so factors away from late brain degeneration need to be carefully considered.

  1. Age – The risk of mortality increases with an increase in the age at injury and with an increase in the current age of the patient, making it a very important factor for life expectancy.15,16 It the starting point for any estimate of life expectancy
  2. Severity of Disability – Of these, mobility and feeding ability are most suggestive of life expectancy, with the highest mortality being seen in those who were not able to walk or feed themselves.15
    1. Mobility – The most powerful predictor of long-term survival, with risk of death being 4 times more in patients with no mobility as compared to those with good mobility.14,15,16 Several other problems that increase mortality such as respiratory problems, pressure sores, infections, cognitive deficits, and the need for ventilator or oxygen support were more common in those who could not walk.14
    2. Feeding – The inability to self-feed is an indirect measure of the patient’s neurological damage and those who required feeding tubes or oral feeding assistance had worse survival rates than those who could feed themselves.14
    3. Post-Traumatic Epilepsy – If present, it indicates a severe brain injury and poses a risk of injury and death from seizures 17
  3. Mechanism of injury – Certain modes of head injury had higher risks of death than others, for example, a TBI due to a fall had a higher risk of long-term mortality than a TBI due to a vehicular crash.16 Though this will not help predict life expectancy in survivors.
  4. Quality of care provided – Advances in the quality of nursing care and rehabilitation services are likely key factors in improving life expectancy.
    1. Rehabilitation – It has been shown to cause significant improvement in the functional status of TBI patients. Rehabilitation for an extended period after the injury has been shown to achieve functional independence in many domains and the ability to follow commands in patients who started off with impaired consciousness during admission to rehabilitation.18
    2. Nursing care – Since several complications that lead to mortality in TBI patients such as mobility issues, feeding problems leading to lung infections, pressure sores, infections, etc can be prevented with good nursing care and the provision of nutrition through a gastronomy, this is likely a major determinant of life expectancy in PDOC.19
  5. Sex – Females have higher survival rates than men.14,15 They also have a great life expectancy.
  6. Social factors – Several social factors affect life expectancy. Factors such as having a higher education, having a job at the time of injury, having a home to go back to after hospital discharge, and not being separated from a partner were associated with lower risks of mortality.16
  7. Maladaptive behaviours – Such as substance abuse and suicide attempts are associated with reduced survival.14


Estimating life expectancy remains one of the most challenging areas to provide guidance to the court as an expert. In brain injury we have limited data sets to provide an accurate estimate and this is most challenging in persistent Disorders of Consciousness. The underlying cause, sex and age are important although the provision of nutrition and high quality nursing care is likely not accounted for in published data sets. High quality care to prevent complications is likely a key factor when attempting to individualise life expectancy in such circumstances.


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