Evaluating a patient with brain injury (traumatic or non-traumatic) is challenging. Appropriate classification of disorders of consciousness (DOC) includes a careful assessment of neurologic function by a neurologist. It is important for palliative care clinicians to understand the diagnosis and the expected time frame during which neurologic function can evolve, so they can educate and counsel families.
Assessment of consciousness and neurologic function are determined by the bedside exam. Brain imaging and neurophysiologic testing are performed to aid in determination of the extent of neurologic injury, but are not definitive for determination of diagnosis and prognosis — which is done by monitoring clinical change over time. A careful mental status exam assessing conscious awareness and wakefulness is critical to establishing the diagnosis of DOC.

Conscious awareness is assessed by response to external stimuli. Purposeful responses (which demonstrate awareness) 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. Reflexive responses occur spontaneously. They include: eye opening, chewing, yawning, crying, and roving eye movements.
Wakefulness indicates arousal due to subcortical and brainstem pathways. It is demonstrated by eye opening and the presence of a 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.

Clinical features of the commonly accepted DOC syndromes.
Coma. 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. The patient does not have a sleep-wake cycle nor do they express emotion. Their motor function is limited to reflexive or postural responses. Coma does not typically last more than several weeks. Those who do not recover progress to brain death, a vegetative state, or a minimally conscious state.
Vegetative State (VS) / Unresponsive Wakefulness State (UWS). UWS is a recently introduced term to describe patients in what has historically been referred to as a VS. These individuals do not demonstrate awareness and remain in an altered state of consciousness for ≥ 28 days from the time of brain injury. 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. They may startle to auditory and visual stimuli, posture or withdraw to noxious stimuli, and have movements of their limbs; however, these represent non-purposeful or reflexive responses.
Minimally conscious state (MCS). This term evolved from the recognition that some individuals do not meet the diagnostic criteria for coma or for VS/UWS. They demonstrate some, albeit “minimal,” level of conscious awareness. Evidence of awareness in an MCS may fluctuate but must be reproducible and sustained and not just a one-time observation. It can be demonstrated by motor or emotional responses, verbalizations, or gestures that are purposeful and not merely reflexive.
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. They will have intact sleep/wake cycles, auditory and visual function, and the ability to experience emotion. In the acute setting, they are quadriplegic and unable to speak or make sounds.
Brain death. Death by neurologic criteria is both a clinical and legal definition. It is defined as death of the individual due to irreversible loss of brain function. There are three clinical exam findings required to determine irreversible brain death, which include coma with known cause, absence of brainstem reflexes, and apnea.

See reference for more information.

Adapted from Foutz RA and Peltier W. Disorders of consciousness (part 1): a practical approach for navigating coma and brain injury. Palliative Care Network of Wisconsin. Fast facts and concepts #382. Internet. Accessed on December 31, 2019