Abstract
Background
Evaluating a patient with brain injury (traumatic or nontraumatic) is challenging. Potential outcomes are often unclear as the manifestations of brain injuries evolve over time and can result in dynamic changes in consciousness. This can create confusion for prognostication and clinical decision making. Appropriate classification of disorders of consciousness (DOC) involves a careful assessment of neurological function at the bedside and an understanding of the expected time frame during which neurological function can evolve. Although neurological assessment and diagnosis is the role of a neurologist, it is important for palliative care clinicians to understand the diagnosis so they can appropriately educate and counsel families. This Fast Fact aims to help clinicians understand the terminology around DOC. Prognosis in DOC will be discussed in a future Fast Fact.
Approach to Examination
Assessment of consciousness and neurological function is determined by bedside examination. Brain imaging and neurophysiological testing are performed to aid in determination of the extent of neurological injury but are not definitive for determination of diagnosis and prognosis, which is done by monitoring clinical change over time. A careful mental status examination assessing conscious awareness and wakefulness is critical to establishing the diagnosis of DOC.
Conscious awareness is assessed by response to external stimuli. Responses can be characterized as purposeful or reflexive. Purposeful responses suggest higher cortical function and can be demonstrated by a meaningful response to motor, auditory, visual, or emotional stimulus. Examples include withdrawing from nail bed pressure, localization to voice, answering Yes or No, following commands, intelligible speech, and/or reaching for or holding objects appropriately. 1 Reflexive responses occur spontaneously and include eye opening, chewing, yawning, crying, or roving eye movements. Purposeful responses demonstrate awareness, whereas reflexive responses do not.
Wakefulness indicates arousal due to subcortical and brainstem pathways. It is demonstrated by eye opening and the presence of a sleep cycle or pattern of wakefulness and sleep. Wakefulness and sleep–wake cycles may occur without awareness or meaningful response to one's environment and do not alone imply consciousness. 2 The dynamic evolution of the neurological examination is often misunderstood by families who may see these changes as indicative of recovery.
Definitions
The clinical features of the commonly accepted DOC syndromes are described in this review.
Coma
It is a temporary state of complete loss of consciousness—both wakefulness and awareness. There is no self-awareness or response to auditory, visual, or tactile stimuli. Individuals are not alert, and eyes are most often closed. They do not have a sleep–wake cycle nor express emotion. 1 Their motor function is limited to reflexive or postural responses. 1 Coma does not typically last for more than several weeks. Those who do not recover progress to brain death, a vegetative state (VS), or a minimally conscious state. 3
VS/unresponsive wakefulness state
Unresponsive wakefulness state (UWS) is a recently introduced term to describe patients in what has historically been referred to as a VS. 4 Both terms are currently in use, and in many state laws and health care directives, VS is used, not UWS. These individuals do not demonstrate awareness and remain in an altered state of consciousness for ≥28 days from the time of brain injury. 5 Unlike individuals in a coma, they demonstrate wakefulness and have sleep–wake cycles. They do not communicate or express emotion although they may cry, smile, or utter noises reflexively. 2 They may startle to auditory and visual stimuli, posture or withdraw to noxious stimuli, and have movements of their limbs; however, these represent nonpurposeful or reflexive responses.1,2 The term “persistent” is used when the condition has been present for more than one month. 4 The diagnosis of permanent VS/UWS has been applied to individuals in a VS/UWS 3 months after a nontraumatic insult (e.g., anoxia) and 12 months after a traumatic brain injury. 6 Recent research demonstrating that a minority of patients eventually will regain consciousness has led to the recommendation that the term permanent vegetative state no longer be used. 5
Minimally conscious state
This term evolved from the recognition that some individuals do not meet the diagnostic criteria for coma or for VS/UWS. These individuals demonstrate some, although “minimal,” level of conscious awareness. Evidence of awareness in a minimally conscious state (MCS) may fluctuate but must be reproducible and sustained and not just a one-time observation. 1 It can be demonstrated by motor or emotional responses, verbalizations, or gestures that are purposeful and not merely reflexive. 1 Despite evidence of consciousness, individuals in an MCS remain profoundly impaired. An individual may evolve to a MCS from a VS/UWS or a coma. This evolution may occur over months to years. 1
Locked-in syndrome
This is not a DOC but is a “do not miss” diagnosis in the evaluation of coma. It is caused by injury to the brainstem. Individuals are fully conscious, yet paralyzed, and can communicate purposefully through blinking and vertical eye movements. 1 They will have intact sleep–wake cycles, auditory and visual function, and the ability to experience emotion. 1 In the acute setting, they are quadriplegic and unable to speak or make sounds. 1 See Fast Fact #303.
Brain death
Death by neurological criteria is both a clinical and legal definition with predetermined standards. 7 It is defined as death of the individual due to irreversible loss of brain function. There are three clinical examination findings required to determine irreversible brain death, which include coma with known cause, absence of brainstem reflexes, and apnea. 7 See Fast Fact #115.
Summary
Determining the correct DOC for individuals with brain injury requires careful repeated bedside evaluations by a neurologist and allowance of time for clinical evolution. Helping families understand what to expect is critically important, including that a patient's clinical picture is expected to evolve, and that developing signs of wakefulness alone does not necessarily mean a patient is recovering conscious awareness or will functionally recover without disability. Anticipatory guidance in these scenarios often involves managing time trials and specialized rehabilitation while also discussing potential treatment limitations for medical setbacks. Unfortunately, there are no absolute time frames for recovery and navigating these uncertainties with families is challenging.