By: Lynn Brouwers, MS, CRC, CBIST
Director of Program Development, Rainbow Rehabilitation Centers

Disorders of consciousness (DOC) are a set of disorders that affect wakefulness. This article focuses primarily on DOC from traumatic brain injury (TBI).

DOC includes coma, the vegetative state (VS) and the minimally conscious state (MCS). These disorders are among the most misunderstood conditions in medicine and are an important challenge for scientific research (The Mohonk Report, 2011). Published estimates of diagnostic error among people with disorders of consciousness range from 30%-40% (Tresch, Sims, Duthie, Goldstein, Lane, 1991; Childs, Mercer, Childs, 1993; Andrews, Murphy, Munday, Littlewood, 1996).

What is a coma? A coma is a state of unconsciousness whereby a person cannot be wakened with touch or noise. The inability to waken differentiates coma from sleep. It is the length of time that a person remains in coma that has commonly been used to decide how severe a person’s brain injury is (see Glasgow Coma Scale).

What causes a coma? The brain stem processes the automatic, unconscious control systems of the body including heart rate, blood pressure, body temperature, and breathing. The reticular activating system (RAS), located within the brain stem, is the important “on/off” switch for consciousness and sleep. ‚‚Reticular Formation Projections with callouts

To be awake, the RAS and at least one cerebral hemisphere must be functioning. ‚‚

If a person loses consciousness, either the RAS has stopped working, or both cerebral hemispheres have shut down.

The reticular activating system stops working in two situations:

  1. Brain stem bleeding or loss of oxygen: Cells in the area of the RAS have lost their blood supply, oxygen, and glucose that the blood supply delivers. This shuts off the reticular activating system.
  2. Swelling: Increased swelling in the brain pushes down on the brain stem causing it to fail. The skull is a rigid box that protects the brain. Unfortunately, if the brain is injured and begins to swell (edema), there is no room for the additional fluid. Increased intracranial pressure causes compression of the brain tissue against the skull bones. This swelling within the skull can cross the midline of the brain and affect the undamaged hemisphere.

If the intracranial pressure continues to increase without being treated, the brain will continue to swell until it pushes down through the opening at the base of the skull, thereby damaging the brain stem where the reticular activating system is located. This affects the ability of the brain to stimulate breathing and control blood pressure and can be the reason for death in the hours or days after injury.

Acute care treatment of coma from swelling

When the members of the trauma team are concerned about swelling of the brain, an intracranial pressure monitor may often be placed inside the skull to monitor the pressure inside. Or, a portion of the skull may be temporarily removed to minimize the risk of further injury to the brain due to the pressure.

Doctors may also “induce” a coma to decrease intracranial pressure and rest the brain. Barbiturate medications such as Pentothal and pentobarbital can be injected similar to providing a general anesthetic. These medications can decrease the metabolic rate. However, an induced coma can make it difficult to use the Glasgow Coma Scale as a predictor of TBI severity.

Coma usually evolves into the vegetative state or a higher level of consciousness within two to four weeks for those who survive (Plum & Posner, 1982).

Glasgow Coma Scale - Disorders of Consciousness

Vegetative state and minimally conscious state

Because of new technologies in functional neuroimaging and electrophysiologic procedures becoming available in the last five years, both American and European experts in the field of DOC are questioning the relationship between brain function and consciousness.

The results of new studies, and the well-documented reports of late recovery, challenge the view that restoration of function in people with severe brain injury is not possible. Cases of late recovery point to the remarkable plasticity of the human brain and its potential for long-term recovery (The Mohonk Report, 2011).

The European Task Force on Disorders of Consciousness has even suggested different names for these states of consciousness; unresponsive wakeful syndrome in place of vegetative state and minimally responsive in place of minimally conscious state. It is hoped that these will infer a less dismal prognosis and may therefore lead to less cessation of treatment in select patients.

“We find it high time to propose a new, more neutral and descriptive term. By calling it ‘unresponsive wakefulness syndrome,’ we describe what we clinically see but do not judge whether there is consciousness or not,” said Dr. Moonen, a member of the Task Force.

Diagnostic Criteria

Coma

All of the following criteria must be evident on bedside examination:

  • No eye opening and absence of sleep-wake cycles on EEG.
  • No evidence of purposeful motor activity.
  • No response to command.
  • No evidence of language comprehension or expression.
  • Inability to discretely localize noxious stimuli.

Vegetative State

All of the following criteria must be evident on bedside examination:

  • No evidence of awareness of self or environment.
  • No evidence of sustained, reproducible, purposeful, or voluntary behavioral responses to visual, auditory, tactile, or noxious stimuli.
  • No evidence of language comprehension or expression.
  • Intermittent wakefulness manifested by the presence of sleep-wake cycles.
  • Sufficiently preserved hypothalamic and brain-stem autonomic functions to permit survival with medical and nursing care.
  • Bowel and bladder incontinence.
  • Variably preserved carian-nerve reflexes and spinal reflexes.

Minimally Conscious State

At least one of the following criteria must be clearly evident on bedside examination:

  • Simple command following.
  • Gestural or verbal yes/no responses.
  • Intelligible verbalization.
  • Movements or affective behaviors that occur in contingent relation to relevant environmental stimuli and are not attributable to reflexive activity. Any of the following examples provide sufficient evidence for this criterion:
  • Pursuit eye movement or sustained fixation that occurs in direct response to moving or salient stimuli.
  • Episodes of crying, smiling, or laughter in response to the linguistic or visual content of emotional but not neutral topics or stimuli.
  • Vocalizations or gestures that occur in direct response to the linguistic content of comments or questions.
  • Reaching for objects that demonstrates a clear relationship between object location and direction of reach.
  • Touching or holding objects in a manner that accommodates the size and shape of the object.

Source: The Mohonk Report. (2011)

“Overall, we hope that this new wording will help to herald a change in the ethical approach towards patients who need more, not less, attention by their environment, since they are not able to claim on their own their right to human contact,” said Dr. Laureys, a member of the task force (European Neurological Society [ENS], 2011).

Although VS and MCS involve severe alteration of self and environment, there is clear and growing evidence that important clinical differences exist. The prognosis is different for VS and MCS. It is difficult to track the incidence of MCS because there is no International Classification of Diseases (ICD) diagnostic code. Estimates are that 315,000 Americans are living with DOC; including 35,000 in VS (New England Journal of Medicine, 1994) and 280,000 in MCS (Strauss, Ashwal, Day, Shavelle, 2000).

VS can be a transient or long-term state following coma. Both the terms “persistent” and “permanent” are controversial, with a practice guideline that the term “permanent” not be used until the VS state has lasted 12 months (Neurology, 1995). Persons in VS may move in a non-purposeful manner and may smile, grimace, tear, and moan. Individuals in VS generally do not visually track or fixate on objects. If tracking is seen, it can often mean that the person is transitioning to MCS.

In the TBI population, 35 percent of individuals who remain in VS for three months will recover consciousness by 12 months post-injury. Among this group, 20 percent will be left with severe disability, while the remaining 15 percent will have a moderate to good outcome (The Mohonk Report, 2011).

Persons in MCS retain large scale cortical networks responsible for language processing, despite their inability to communicate reliably (Schiff, et al., 2005). The recovery for this population is slow and long. In the MCS group, 50 percent will have moderate to severe disability while 27 percent will have mild to moderate disability (Giacino & Kalmar, 1997; Whyte, et al., 2005).

Assessment of Consciousness

Since consciousness cannot be directly observed, clinicians must observe behavior and draw conclusions about an individual’s underlying state of consciousness. The Brain Injury-Interdisciplinary Special Interest Group, Disorders of Consciousness Task Force, composed of experts from the American Congress of Rehabilitation Medicine, reviewed available scales and made evidence based recommendations for clinical practice (Seel, et al., 2010).

The scale, JFK Coma Recovery Scale-Revised, (CRS-R), received the highest recommendation. The scale consists of 23 items that comprise six subscales addressing auditory, visual, motor, oromotor, communication, and arousal functions. The scale is free and available at www.tbims.org/combi/crs/index.html (Giacino & Kalmar, 2006).

The Mohonk Report

A report was delivered to Congress in 2011 by an esteemed group of rehabilitation specialists, physicians, and researchers, requesting funding and support nationally for a specialized neurorehabilitation center and a structured support network. Their concerns were that the current system of care (acute care followed by transfer to a nonspecialized skilled nursing facility or discharge home) makes long-term research difficult and may be responsible for the poor outcomes for many people with disorders of consciousness.

It is especially important to know how many individuals are in minimally conscious state and have a “life of the mind,” but are misdiagnosed as vegetative state. The prospect of such individuals harboring consciousness but being misidentified or simply ignored because of the perceived futility of additional long-term assessment is an ethical concern. Lack of specialists and specialized care centers also perpetuates the historic disregard of this marginalized population (Fins, 2003).

References