Defining Consciousness

Consciousness has two parts—wakefulness (being awake or asleep) and awareness (perceiving one’s self or surroundings) through feelings, thoughts, and one or more of the five senses—sight, hearing, smell, taste, and touch.

In 1995, the AAN issued guidelines for assessing and managing patients in the persistent vegetative state, which it defined as a "clinical condition of complete unawareness of the self and the environment accompanied by sleep-wake cycles." In addition, the definition included either complete or partial preservation of hypothalamic function—releasing hormones, regulating body temperature—and brainstem autonomic function such as breathing, regulating heart rate, blood pressure, and sleep/wake cycles, and swallowing. In 2002, the Aspen Neurobehavioral Workgroup defined a minimally conscious state as a condition of severely altered consciousness characterized by minimal but definitive behavioral evidence of self or environmental awareness.

Since the publication of the 1995 AAN guidelines and the 2002 Aspen Neurobehavioral Workgroup report, research on disorders of consciousness has outdistanced previous definitions and practice recommendations.

Assessing Awareness, Redefining Terms

To update the guidelines, an international panel of experts convened by the AAN, ACRM, and NIDILRR that included an AAN methodologist, patient representatives, and staff conducted a comprehensive review of the literature related to the diagnosis, natural history, prognosis, and treatment of disorders of consciousness, with a specific focus on patients with disorders of consciousness for 28 days or longer.

The review panel cited research that concluded that about four in 10 people who are thought to be unconscious are actually aware.

In an analysis of new evidence and a re-analysis of data from the 1994 AAN Multi-Society Task Force on the definition of "permanent" vegetative state—three months after a nontraumatic injury leading to a vegetative state and 12 months following a traumatic injury—the panel concluded the term should be replaced with "chronic" and include how long the patient has been in that state. The term “permanent” implies irreversibility, the researchers said, which may be inaccurate given the frequency with which patients recover after the time points recommended in the 1994 report. The panel also emphasized the importance of maintaining access to long-term care and support for these patients as most of them will remain fully or partially dependent.

The panel did not find any evidence to support or refute a change to the 2002 case definition of minimally conscious state (MCS), but acknowledged a recent proposal to further group these patients as MCS+ and MCS-, based on the presence or absence of signs of preserved language function such as the ability to follow commands or understand speech.

Early Diagnosis May Enhance Recovery

Clinicians with specialized training in managing disorders of consciousness should perform a standardized behavioral evaluation immediately after the injury and conduct repeated tests during the first three months after a brain injury because of shifts in levels of arousal and frequent medical complications that can lead to less accurate diagnoses, according to the panel.

Studies that tracked functional outcome beyond one year suggested that up to one in five patients who sustained a severe brain injury from trauma with ongoing disturbance in consciousness on admission to inpatient rehabilitation eventually recover and are able to function independently at home and may be able to return to work.

In addition, patients in a minimally conscious state due to brain injury from trauma have a better chance of more favorable outcomes than patients with disorders of consciousness caused by disease or illness, including stroke, heart attack, or brain bleed, although this depends on the time since injury.

Drugs May Speed Up Recovery

Few treatments for patients in a vegetative state have been reviewed carefully, but researchers said amantadine, an antiviral drug approved by the US Food and Drug Administration to treat the flu and Parkinson’s disease, can accelerate recovery for people in a vegetative or minimally conscious state after a traumatic brain injury when used within one to four months after the initial injury.

New Guidelines Can Lead to Better Recovery

In the United States, about 4,200 people per year are in a vegetative state, according to the panel. The number of people in a minimally conscious state is unknown, mainly because this state of consciousness has no diagnostic code, but researchers estimates the range to be between 100,000 and 300,000 people.

The new guidelines are intended to help improve diagnosis and prognosis for patients in vegetative and minimally conscious states caused by brain injury and help guide an evidence-based approach to care.

“Misdiagnosis may result in premature or inappropriate treatment withdrawal, failure to recommend beneficial rehabilitative treatments, and worse outcome. That is why an early and accurate diagnosis is so important," the panel concluded.

For more about disorders of consciousness, read our expert’s explanation of the differences between coma, minimally conscious state, persistent vegetative state, and brain death.