PDOC: emergence
Last updated: 25 May, 2025
Most transitions from an unconscious state to a conscious state are quick and often go unnoticed or unremembered by the person. The most common case of unconsciousness is sleep, and most people suddenly find themselves awake. An observer may notice a short episode of slight confusion, lasting a few seconds. After an anaesthetic or concussion, the process of waking up may be slightly prolonged, with a period of being awake but confused, or a brief return to sleep. When someone has been unconscious for days or weeks, the boundaries between being awake, being conscious but confused, and being fully conscious are often unclear and ambiguous. This post considers the ending of a prolonged disorder of consciousness, which, if the person does become unquestionably fully conscious, is termed a process of emergence from a PDOC. I found little research into the validity or accuracy of diagnosing the return of consciousness. On this page, I suggest distinctions between consciousness at the instant, being conscious as judged by existing criteria, and useful consciousness that enables a person to perform significant, purposeful activities.
Table of Contents
Introduction
Diagnosing and managing patients with a prolonged disorder of consciousness dramatically illustrates a universal problem in healthcare, and indeed in life: what features unequivocally separate two adjacent states, such as ‘normal’ or ‘abnormal’, sick or well, conscious or unconscious, has multiple sclerosis or does not, and so forth. In law, challenging cases are decided by a jury, a tribunal, or a single judge. The process is costly and slow, relying on the collection of sufficient evidence and the construction of sound, logical justifications.
In healthcare, boundary decisions must be made daily by all professionals: Is this electrocardiogram sufficiently abnormal to inform a treatment decision, or is the tremor sufficiently characteristic of Parkinson’s disease to warrant a specific treatment? When a resource, such as a disease-modifying drug for multiple sclerosis, is available, advisory organisations, such as the National Institute for Health and Care Excellence (NICE), employ strict criteria to limit its use to those most likely to benefit.
One solution is to look for patterns while avoiding undue dependence on one or two criteria. Most healthcare decisions take into account the full range of clinical information. This usually leads to better decisions—until the pattern itself is systematised and reduced to a list of criteria. This caveat applies to many diagnoses, including chronic fatigue syndrome, depression, non-epileptic attacks, and irritable bowel syndrome.
The consequences of brain injury or disease illustrate the problem. What is the post-concussion syndrome, and how is it diagnosed? How does one determine the severity of brain damage? When is someone disabled? Can someone with Parkinson’s Disease drive safely, given that their problems usually fluctuate?
The question considered here is how to decide when someone has emerged from PDOC.
PDOC: levels of consciousness
Clinically, the unconscious state is measured using the Glasgow Coma Scale, which is invaluable in the acute phase. Traditionally, scores of 8/15 or less indicate unconsciousness. This measure immediately illustrates several critical features of consciousness.
Consciousness is a continuous variable; it is not a binary phenomenon; it is a spectrum. A person scoring 3/15 is more deeply unconscious than someone scoring 8/15. Conversely, a person scoring 9/15 is much less conscious than someone scoring 15/15.
The very lowest level is also described as coma, and its defining feature is that the person never opens their eyes. This typically indicates a lack of arousal, which illustrates that consciousness has two components: being awake and having an active mental function that influences the content of the awake being’s mind. If a person cannot be aroused, it is impossible to determine their cognitive functioning.
The Glasgow Coma Scale depends entirely on the behavioural response to stimuli, which, in the Glasgow Coma Scale, are mainly pain. As consciousness recovers, the responses become more complex. The lower levels of complexity are insufficient to say someone is conscious.
The scale becomes less appropriate in the non-acute phase of a neurological condition. Bryan Jennett, who developed the Glasgow Coma Scale, also coined the term, vegetative state to describe people left unconscious for months or years after brain damage. He observed that almost every unconscious person re-established a sleep-wake cycle within a few weeks of onset, but many people showed no other meaningful behaviour.
Thirty years after his first paper, he wrote, “What attracts attention and curiosity is the dissociation between arousal and awareness—the combination of periods of wakeful eye opening with lack of any evidence of a working mind either receiving or projecting information.” The apposite phrase often used is, “The lights are on but no one is in.”
In 1993, in the UK, the diagnosis of the Permanent Vegetative State became legally relevant, as it was associated with the legally sanctioned withdrawal of feeding and hydration. (Airedale Hospital Trustees v Bland) Attention became focused on establishing whether someone was in the vegetative state, and soon realised the large spectrum between absolute absence of awareness and full consciousness.
Eventually, in 2002, Joseph Giacino et al. introduced the next significant classification, the Minimally Conscious State (MCS), which was later subdivided further into plus and minus levels.
The global term, a prolonged disorder of consciousness, was introduced in the Royal College of Physicians’ “Prolonged Disorders of Consciousness. National Clinical Guidelines” (2013). The term encompassed all categories of unconsciousness.
In summary, consciousness has consistently been recognised as a continuous variable in acute situations; however, for approximately 40 years (1972-2012), it was considered to consist of separate, categorical states.
Behavioural evidence of consciousness.
Like the Glasgow Coma Scale, the Coma Recovery Scale – Revised is a behavioural measure of consciousness widely used to detect change in the level of consciousness. It has 23 items that record behaviours occurring after different sensory stimuli. It has been used to distinguish between the vegetative state and the minimally conscious state, and to define a boundary between the minimally conscious state and full consciousness.
The behaviours that may be seen in a person who is still unconscious, albeit minimally conscious are shown in Box 3 (diagnostic criteria of minimally conscious state) in Disorders of Consciousness Classification and Taxonomy published in 2024 by Katherine Golden et al:
- Following simple commands;
- Gestural or verbal yes/no responses regardless of accuracy;
- Intelligible verbalization;
- Purposeful behavior including movements or affective behaviors that occur in contingent relation to relevant environmental stimuli and are not due to reflexive activity, including
- Vocalizations or gestures that occur in direct response to the linguistic content of questions:
- [many other examples are given]
Brief episodes of complex purposeful behaviour are compatible with being unconscious, a phenomenon that I discuss later.
Emergence from PDOC.
The Coma Recovery Scale – Revised was also used to develop a behavioural boundary between being unconscious and being considered conscious; the phrase used was that the criteria confirmed “emergence from” the minimally conscious state.
The 2020 edition of the UK Royal College of Physicians’ “Prolonged disorders of consciousness following sudden onset rain injury: National Clinical Guidelines” gave a slightly expanded set of criteria to determine if someone had emerged:
Emergence from PDOC - criteria:
Patients should demonstrate a consistent response on at least one of the following types and should do so whenever awake (eyes open) and presented with the situation:
- functional use of objects
intelligent use of at least two different objects on two consecutive evaluations, with or without instruction. For example, writes or draws using a pen or pencil and uses a comb or a hairbrush to brush hair. - Consistent discriminatory choice making
consistently indicates the correct choice from two pictures on 6/6 trials on two consecutive occasions, using at least three different picture pairs.
They should also show functional interactive communication giving:
- evidence of awareness of self
gives correct yes/no responses to 6/6 autobiographical questions on two consecutive evaluations - evidence of awareness of their environment
gives correct yes/no responses to 6/6 basic situational questions on two consecutive evaluations.
The key feature is evidence of complex, purposeful behaviours that are both consistent and repeated whenever the eyes are openi.e. when the person is aroused and awake). One must understand that some people with a specific language impairment may show evidence of awareness of themselves and their environment through behaviour and non-verbal communication.
The Wessex Head Injury Matrix (WHIM) is often used to assess and track changes in responsiveness. It includes 63 behaviours, and six are characteristic of emergence. While there is no specific score to determine return of consciousness, until the total number of behaviours consistently exceeds 32/63, emergence is unlikely, and at thee time of emergence, the mean (SD) score was 49 (12) out of 63 in the study by Turner-Stokes et al (2015).
The UK Rehabilitation Outcomes Collaboration (UKROC) database collects data on the UK FIM+FAM (Functional Independence Measure and Functional Assessment Measure). Richard Siegert et al. used that outcome measure as a behavioural marker of recovery from consciousness in an exploratory investigation of 1170 patients. A score of 31/210 or 30/210 (the lowest possible score) was indicative of being in a minimally conscious or vegetative state, whereas a score of 36/210 or higher would indicate being conscious. Intermediate scores are indeterminate.
In a study on nine people who emerged after traumatic brain injury by Christine Taylor and colleagues, object use occurred before functional communication, two had the opposite order, and five recovered both types of behaviour at the same time.
Willemijn van Erp and colleagues investigated unexpected late emergence in a prospective cohort study involving 31 patients. Four patients appeared to show emergence later than expected; however, careful review in all four cases revealed undoubted evidence of consciousness at an earlier stage in three. The fourth had an obstructive hydrocephalus, a treatable complication; the loss of reactions indicating early improvement was not detected.
One may conclude that behavioural observations indicate that someone has emerged. In clinical practice, specific behavioural criteria are typically the most suitable; at times, other measures, such as the Wessex Head Injury Matrix, may provide evidence. The justification for concluding that someone has emerged should be documented.
The challenge of a boundary.
Although the methods just described appear to give a clear boundary between a conscious state and an unconscious state, in clinical practice, the situation is less clear-cut.
People vary; we all have good days and bad days. Consciousness varies; we all have periods of sleep every day. Often, upon waking, we may be slightly confused, and when stressed, we may experience heightened awareness. People with a prolonged disorder of consciousness are no different, and variability has been well-recognised though often overlooked.
As people transition from unconsciousness to full awareness, they may pass through intermediate states. Although we subjectively realise we are awake suddenly, an observer may see signs of waking, and the waking person may even speak (e.g., say ‘go away!’).
People with a prolonged disorder of consciousness, defined as lasting more than four weeks, typically undergo a phase of waking up, often referred to as emergence. Before finally becoming conscious, the person will likely fluctuate between being conscious and unconscious, a phenomenon that could be termed an emerging phase.
The widely recognised behavioural criteria suggesting someone is in the minimally conscious state rather than the vegetative state include several behaviours that many people would consider indicative of consciousness, such as following simple commands.
A similar issue arises when separating the vegetative state from the minimally conscious state. For example, the Multi-Society Task Force on PVS referred to signs of visual function thus: “extremely cautious when making a diagnosis of the vegetative state when there is any degree of sustained visual pursuit, consistent and reproducible visual fixation, or response to threatening gestures.” I discussed other issues related to this boundary in 2017.
How does one determine that someone is conscious? Is it entirely based on evidence of language use? Hacker and Bennett consider that the successful use of language is critical for self-awareness. Someone with severe aphasia (impairment of language) will usually be considered conscious, but how do we decide this? When someone unequivocally shows behavioural evidence of consciousness, such as responding accurately to a question or complex command, should they be considered conscious after one single short (30-second) episode with no other episodes in five years?
What is “being conscious”?
The crucial question concerns how clinical teams might evaluate consciousness, particularly in answering the question, “Is this person conscious?”
Many books discuss what consciousness is, primarily from a philosophical or neuro-cognitive perspective. These discussions and resultant definitions are not easily transformed into a helpful clinical description. They also consider consciousness as if it were a stable state, whereas in people with severe brain damage, consciousness varies and may be evanescent ([OED] “soon passing out of sight, memory, or existence; quickly fading or disappearing”).
Clinicians require evidence using data collected in a clinical or community setting; it cannot depend on sophisticated technology. It will, therefore, mainly be based on behaviours.
The question does not concern transient episodes of consciousness that occur occasionally; it concerns being conscious enough to allow the person to achieve some functional goal. For example, an episode where a farmer gives the correct name for a white duck, but shows no other behaviour over four years, is not considered conscious. [see left-hand column on page 442 of this paper.]
I am overlooking transient episodes because they are typically relatively infrequent, rarely predictable, and insufficient to allow the person to exercise any autonomy or achieve any significant behavioural goal. They do not allow the person to establish or progress a meaningful relationship with another person, such as a family member.
The question could be phrased as contrasting being conscious, which concerns the instant the question is asked, and being in a conscious state, which concerns the person being predictably awake and responsive for periods of every day sufficient to achieve something.
Behavioural evidence of useful consciousness.
A conscious person can think, plan, and execute activities over a significant period. Upon rising in the morning, a minimum of 20 minutes will be required. Shopping, gardening, feeding, and using the toilet are activities that demand continuous attention for many minutes to several hours. Although one cannot specify a precise duration needed to be considered conscious, simply getting up, feeding, and going to bed may take three or more hours each day.
Therefore, the temporal aspect of a clinical description of consciousness must include both the longest single period of sustained attention observed and the total time aroused (i.e. awake and sustaining attention) in 24 hours.
A conscious person shows meaningful or appropriate reactions to stimuli, usually external. The person will, for example, pick up and use objects for their purpose, react to darkness by turning on a light, converse or interact with others, and avoid dangers. The complexity of the response will vary according to the degree of cognition, but the person’s reactions to stimuli must show a basic understanding of the situation and how to react.
The most common interaction demonstrating awareness is conversation: the person can demonstrate the use of language, turn-taking shows awareness of others, and responding appropriately indicates understanding. However, non-linguistic social interaction is equally informative.
Lastly, a conscious person should demonstrate agency, which involves the initiation and completion of tasks without external prompting. A person who never initiates anything, just waiting, may be conscious but severely depressed, lacking drive, or have Parkinson’s disease (for example).
A clinical description is vital because people with a prolonged disorder of consciousness who improve will inevitably experience brief periods of more complex behaviour, either spontaneously or in response to something. However, a few seconds of complex behaviour daily or hourly cannot be considered indicative of a “returned consciousness”; it might be the first indication of eventual recovery when someone has only been unconscious for eight weeks after a traumatic brain injury. In someone five years after hypoglycaemic brain damage, it will simply be variability within a border zone.
Thus, in behavioural terms, to be functionally useful, a conscious person needs:
- To be aroused and attentive for periods of at least 10-20 minutes for at least three hours daily
- To show responses to stimuli that
- require an understanding of the meaning or implication of the stimulus
- demonstrate an appropriate purpose
- To exhibit spontaneous (self-initiated) purposeful behaviour without external cues
Shorter, less sustained and incomplete behaviours may show one or more of these characteristics but are insufficient to qualify as achieving a state of consciousness.
People who meet the criteria for emergence discussed earlier will likely achieve ‘useful consciousness’ as described here.
Consciousness, feelings, and experience.
Do behaviours that typically accompany feelings of happiness, distress, pleasure or pain constitute substantial evidence of consciousness in the absence of other evidence? I have discussed this concerning pain on another page, where I assume that it does not. Before discussing it further, I will report on two memorable cases that gave behavioural evidence of experiencing emotions, not pain.
PDOC, emergence, emotional feeliings
The first, whom I will call Charles (obviously not the patient’s actual name), was a 72-year-old man who had sustained severe generalised brain damage after an accident about 9 months before I saw him. His care had been in specialist neuroscience wards throughout, including a neurological rehabilitation service with long experience of patients with prolonged disorders of consciousness. No one had reported any behaviours suggesting consciousness at any level.
When I went to see him with an occupational therapist, he was in his wheelchair outside his room. We said a brief hello, and we moved him back to his room, talking to him as we did so. He did not react at all. I then introduced myself formally, saying “Hello Charles. I am Dr Wade, Derick Wade. I have come to see you to give you, your family, and the clinical team here my advice.”
As I reached the end of this preamble, his face crumpled, looking extremely distressed, and he started crying with tears, groaning and wailing, and his respiration rate increased. The occupational therapist and I were distressed too, and tried unsuccessfully to comfort him. Over about 60-90 seconds, the behaviours abated and stopped.
I then examined him, and he did not react to any stimuli, auditory, visual, or somatosensory. There were no spontaneous movements. Just before we left, I gave a formal goodbye, thanking him for his time. He showed an identical emotional reaction, and the episode lasted about 90 seconds.
The only common feature was that I tend to adopt a different tone of voice when saying hello or goodbye in these circumstances. I discovered several reports in his detailed care records of similar episodes to nurses or family members when first saying hello.
The second case was a younger, 46-year-old man with extensive brain damage one year before. He, too, had been in a specialist setting throughout. He had occasional episodes of complex behaviour lasting a few seconds at most, and he fulfilled the criteria for the minimally conscious state. Still, he had never approached the criteria for emergence.
Care staff and family reported spontaneous episodes where his behaviours were typical of emotional distress, usually, with a few being typical of happiness (e.g. laughing and looking happy). They lasted about a minute. No one had noticed any obvious precipitant; they were not related to any care procedures or stimuli that would be expected to cause pain or pleasure.
As I argue for the behaviours typically associated with pain, one cannot assume a disconnection between behaviours typically associated with a specific emotional state and the feeling of that state. It is possible that the person may experience feelings of distress or happiness when exhibiting these behaviours.
These episodes may be evidence that variability also occurs in emotional manifestations. At a lower level, family members and care staff often report that someone smiled, looked puzzled, seemed to cry, grimaced etc. The usual response of ‘experts’ is that the observer is misinterpreting spontaneous movements; tears are usually attributed to physiological tear production to lubricate the cornea.
However, just as we observe brief periods of more complex cognitive behaviours, we should presumably not be surprised to see brief behaviours indicative of an emotion.
Conclusion
This discussion of consciousness in people who have a prolonged disorder of consciousness has made several points:
- Behaviours are the only evidence available to evaluate consciousness
- Consciousness is a continuous variable with no absolute boundaries allowing categorisation
- A person’s level of consciousness varies, and brief episodes of more complex behaviour indicative of conscious cognitive processing or emotional states are not rare
- Emergence from a prolonged disorder of consciousness requires evidence of complex, purposeful behaviours that are both consistent and repeated whenever the eyes are open
- ‘Useful consciousness’ requires sustained active cognition for several hours daily, with episodes lasting at least 15 minutes.